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PLC Program for Entry/Exit Control of Car Parking


This is PLC Program for Entry/Exit control of the basement or underground car park.

Problem Description

Due to crowded area we face lots of problems of vehicle parking at basement or underground at shopping mall, hotels, complex etc.

This is happening due to contradiction between the rapidly growing number of vehicles and limited parking spaces in malls, shop and complex in cities results in the phenomenon of “difficult parking and disorderly parking”.

Current parking problem has serious impacts on people’s quality of life and the running of roads.

Problem Diagram

PLC Program for Car Parking

Problem Solution

By simple automation we can reduce the car parking problem at basement or underground in shopping mall, hotels, complex etc. The Entry/Exit at basement is a single lane passage and it needs traffic lights to control cars.

Here we consider two lights indication for cars control. Red lights prohibit cars entering or leaving while green lights allow cars entering and leaving.

When car enters at the passage from the entry of the ground floor, both red lights (ground floor and basement) will be ON. Other car entering and leaving is prohibited during the process till the car passes through the single passage. When passage is clear both green lights (ground floor and basement) will be ON and allow other cars entering from the ground floor or basement.

Initially we will keep green lights ON and red light OFF


Here is PLC program for Entry/Exit control of the basement or underground car park.

List of Inputs/Outputs

Inputs List:-

  • Main SWITCH = I0.0
  • Sensor S1 for ground floor Entry/Exit = I0.1
  • Sensor S2 for basement Entry/Exit = I0.2

Outputs List:

  • Green light (Entry/Exit ground floor) = Q0.0
  • Green light (Entry/Exit basement) = Q0.1
  • Red light (Entry/Exit ground floor) = Q0.2
  • Red light (Entry/Exit basement) = Q0.3

M memory coil List:

  • M10.0=Will be ON when car passes sensor S1
  • M10.3=Will be ON when car Passes sensor S2
  • M0.0 = Positive edge of system ON
  • M0.1 & M11.0 = Positive edge of sensor S1
  • M0.3 & M11.1 = Positive edge of sensor S2
  • M11.2 = Negative edge of sensor S2
  • M11.3 = Negative edge of sensor S1

Ladder diagram for Entry/Exit control of the basement or underground car park

Program Description

In this application we have used Siemens S7-300 PLC and TIA Portal Software for programming.

Network 1: As per above explanation in first network when system is ON (I0.0), initially both green lights (ground floor (Q0.0) and basement (Q0.1)) will be ON .SET instruction is executed and it will set both output Q0.0 and Q0.1.

Network 2: As per above explanation in second network when system is ON (I0.0), initially both red lights (ground floor(Q0.2) and basement(Q0.3)) will be OFF. RESET instruction is executed and it will reset both output Q0.2 and Q0.3.

Network 3: When car enters in the empty passage from the ground floor, sensor S1 (I0.1) will be triggered and with this trigger, memory coil M10.0 will be SET.

Network 4: When car enters in the empty passage from the basement, sensor S2 (I0.2) will be triggered and with this trigger, memory coil M10.3 will be SET.

Network 5: Both red lights will be set by either positive trigger of sensor S1 or sensor S2. Because when car enters in empty passage then both red lights (Q0.2 &Q0.3) will prohibit car entry/exit from both side.

Network 6: Here we have taken negative trigger of both sensor S1 (I0.1) and S2 (I0.2) so when they triggered red lights (Q0.2&Q0.3) will be OFF. When car completely passes empty passage then red lights (Q0.2&Q0.3) should be OFF.

Network 7: In this network green lights (Q0.0&Q0.1) will be ON when red lights are OFF. Green lights (Q0.0&Q0.1) allow other car for entry or exit.

Network 8: If red lights (Q0.2&Q0.3) are ON at that time green lights (Q0.0&Q0.1) should be OFF. So in this network when red lights (Q0.2&Q0.3) ON at that time reset instruction will be executed and green lights (Q0.0&Q0.1) will be OFF

Network 9: If system ON (I0.0) SWITCH is OFF then all memories should be 0.Here we have taken MOVE instruction for moving zero in all memories (MB0, QB0, and MB10).

This Example is for concept explanation only, not all parameters are considered in this example (such as door open/close system, alarms etc.)

Runtime Test Cases

PLC Ladder Logic for Car Parking

Note : The above PLC Logic provided for basic idea about application of PLC in Car Parking Control of Entry/Exit Gates. The Logic is limited and not complete application.

Article by
Bhavesh Diyodara

Digital Control Valve (DCV) Calibration Procedure



The below calibration procedure for Digital Control Valve. Make : Fisher, Model :  DVC 6000

Also Read : Digital Control Valve Principle

Tools Required:

1. 375 Field communicator
2. Tools kit
3. DATA sheet

Calibration Procedure

  1. Take the work permit from shift in-charge
  2. Checking for valve accessories any damage for DVC feed back, guage, air regulator and filter
  3. Check the pressure regulator guage and set it according to bench set
  4. Check the positioner cam alignment ,cam alignment should be matched with travel length
  5. Operate the valve from DCS, observe the valve travelling condition , if it is not matching with our requirement then we have to connect the 375 field communicator at positioner terminal ( ie. Loop + and -)
  6. Switch on the communicator then select FF application in Communicator.
  7. Select required tag number from list ,then select transducer block and select configuration setup
  8. Again click basic setup enter in to setup wizard, transducer go to manual mode for performing setup
  9. As per data sheet , check the data’s whether it is matching or not
    a) Travel length
    b) Check the pressure unit (psi or kg/cm2)
    c) Check actuator manufacture and model number and actuator size
  10. Now we will go for auto calibration standard than select manual crossover adjustment
  11.  Then check visually whether feedback arm is matching with the hole of the DVC body or not?
  12. Run performance tuner and check the valve operation
  13. Calibration over than change the valve auto mode
  14. Check for valve stroke after auto calibration from DCS


  • If Valve hunting is vigorously
    a) Go to detail setup
    b) Go to response control
    c) Click travel tuning

For fisher control valve adjust travel tuning set to lower alphabet ( If setting was D we have to select C).

For other valves we have adjust proportional gain

  • If Valve is over shooting
    a) Go to detail setup
    b) Go to response control
    c) Click pressure tuning

For fisher control valve adjust pressure tuning set to lower alphabet ( If setting was D we have to select C).

For other valves we have adjust proportional gain


Relay – A = Double Acting
Relay –B = Reverse acting
Relay –C = Forward & Reverse acting

Article by

Gas Detectors Interview Questions & Answers


How carbon monoxide detectors work?

Carbon monoxide detectors sound an alarm when they sense a certain amount of carbon monoxide in the air over time. Different types of alarms are triggered by different types of sensors.

  • Biomimetic sensor: A gel changes color when it absorbs carbon monoxide, and this color change triggers the alarm.
  • Metal oxide semiconductor: When the silica chip’s circuitry detects carbon monoxide, it lowers the electrical resistance, and this change triggers the alarm.
  • Electrochemical sensor: Electrodes immersed in a chemical solution sense changes in electrical currents when they come into contact with carbon dioxide, and this change triggers the alarm.

Once the alarm sounds, the carbon monoxide detector must be in a carbon monoxide-free environment to reset itself.

What are TWA and STEL?

TWA stands for Time Weight Average. This in reference to dosages of toxic gas you may encounter in the work place. It is based on an 8 hour day/ 40 hour work week. TWA is a term established by the American Conference of Governmental Industrial Hygienists (ACGIH). STEL stands for Short Term Exposure Limit. This is the average amount of gas you can be exposed to in a 15 minute period with no long term health effects. This may occur 4 times a day. STEL is a term established by the ACGIH.

Explain about Common units for measuring concentration ?

% (percent)

This unit expresses concentration in parts per hundred (percentage) of a substance in 100mL of a medium such as air.

ppm (parts per million)

This unit that expresses concentration in parts per million is measured as the volume (denoted in litres [L]) of a substance found in 1L of a medium such as air.

mg/m3 (milligram per cubic metre)

This unit expresses the concentration in one cubic metre of air (equivalent to 1L or 1000mL) of a substance in terms of its mass (measured in milligrams). It is primarily used for particle-like substances, and only rarely for gaseous concentrations.

mg/L (milligram per litre)

This unit expresses the concentration in one litre of air (1000mL) of a substance in terms of its mass (measured in milligrams). It is generally used for measuring concentrations in liquids, and only rarely for gaseous concentrations.

Explain different Gas Conversion Formulas for Converting from one unit of concentration to another ?

Gas Unit Conversion Formula

M: Molecular weight of a substance
22.4(L): The volume of 1 mol at 1 atmospheric pressure at 0ºC
273(K): FK stands for Kelvin, the unit used to measure thermodynamic temperature; as 0ºC corresponds to 273.15K.
You simply need to add 273 to the Celsius/Centigrade value (273+T) to obtain the temperature in Kelvin
1013(hPa): One atmospheric pressure
P: P denotes the atmospheric pressure at the point of measurement (hPa)

How often do we need to calibrate gas monitor?

This is a controversial subject. OSHA would have you calibrate your gas detector before each use. In practice, our customers come up with their own intervals. If the gas monitor is used infrequently, say once a month, it should be calibrated every time to give you confidence that the unit is going to respond as it should. If your company uses its detection device a few times a week, then our customers have told us they do an occasional bump test and calibrate less often.

How to clean gas monitor?

You should follow each manufacturer’s directions. For BW Honeywell Gas Detectors the manufacturer recommends the use of a soft damp cloth. The only approved cleaner is ACL Staticide. You should avoid exposing the sensor screens to moisture. DO NOT use computer keyboard air dusters to clean debris from sensor filters or products such as EconoClean, WD40, etc. as these will destroy the sensors.

What is Oxygen Deficiency?

The most widely accepted definition is that air is oxygen deficient whenever concentration is less than 19.5%. This occurrence is often associated with confined spaces, unventilated cellars, sewers, wells, mines, ship holds, tanks, and enclosures containing inert atmospheres. Typical causes are displacement, microbial action, oxidation, combustion and absorption.

What is a Confined Space?

In terms of OSHA and NIOSH safety requirements, a “confined space” refers to an area whose enclosed environment and limited access make it dangerous to people working there. Anywhere access or egress is limited, or that may contain hazardous atmospheres (too low or enriched oxygen levels, toxic or flammable gases) will likely be classified as a confined space for workers. Confined spaces can be above or below ground level. Examples of confined spaces include inside airplane wings, tanks, pipes and sewers, ventilation shafts, electrical service rooms, vats, and silos.

Gas Detection below terms used generally :

  • LEL – Lower Explosive Limit. The minimum concentration of a combustible gas or vapor in air which will ignite if a source of ignition is present
  • UEL – Upper Explosive Limit. Most, but not all, combustible gases have an upper explosive limit which is the maximum concentration in air which will support combustion. Concentrations which are above the U.E.L. are too “rich” to burn.
  • PPM – Parts Per Million (toxic & VOC)
  • %VOL – Percent by volume (oxygen)
  • VOC – Volatile Organic Compounds (PID)
  • PID – Photo Ionization Detection (VOC)
  • TWA – Time Weighted Average (toxic gases)
  • STEL – Short Term Exposure Limit
  • IP – Ionization Potential & Ingress Protection
  • IS Rating – Intrinsic Safety (UL, CSA)
  • T90 – Time sensor needs to reach 90% full response

What are the three basic kinds of atmospheric hazards?

  • Oxygen (deficiency and enrichment)
  • Flammable gases and vapors
  • Toxic contaminants

What is LFL  ?

Lower flammability limit (LFL) usually expressed in volume percent, is the lower end of the concentration range over which a flammable mixture of gas or vapour in air can be ignited at a given temperature and pressure. The flammability range is delineated by the upper and lower flammability limits. Outside this range of air/vapor mixtures, the mixture cannot be ignited (unless the temperature and pressure are increased).

What is ppm.m?

ppm.m (parts per million metre) is the recognised unit of measure for a toxic or flammable gas being detected over an open path. For example 250 ppm.m can represent a 1 meter wide gas cloud whose concentration is 250 ppm of the target gas or a 2 meter gas cloud with a concentration of 125 ppm.

What Is a Bump Test ?

A bump test is a brief exposure of the sensor to gas and verifies if the sensor is responding and the alarm is functioning.

Why is LEL important in Combustible Gas Detection ?

In environments with combustible gas hazards, it is important to know long before the gas concentration reaches the LEL. Typical safety standards require that a gas detection unit give warnings at 10 – 20% of the LEL. Do not confuse the alarm level with the volume of gas required to reach the LEL. For example: Methane has an LEL of 5% by volume in air. For a gas detector to give an alarm at 10% of the LEL, it must trigger when it detects 0.5% by volume. The detector for this application would most likely be calibrated for the range from 0% to 5% gas by volume, but display the reading as 0 – 100% LEL.

If you have a flameproof fixed detector (Ex) can you make it “intrinsically safe” (IS) by using a zener barrier or galvanic isolator?

No, a flameproof detector “safety protection” cannot be changed by using a zener barrier or galvanic isolator of any sort. It can only be used as a flameproof device.

If you have a “intrinsically safe” (IS) fixed detector do you need a zener barrier or galvanic isolator when used in a hazardous zoned area 0, 1 or 2 for example?

Yes you must use a zener barrier or a galvanic isolator to comply with the detectors certification requirements.A zener barrier or Galvanic isolator must be used when a “intrinsically safe” (IS) detector is used in a hazardous zoned area.

What are the mounting heights for CO gas detectors and NO2 gas detectors?

Carbon Monoxide (CO) gas has a slightly lower density than air. Recommended mounting height for Carbon Monoxide (CO) gas detector is 1.5 m above floor.

Nitrogen Dioxide (NO2) gas is heavier than air and sinks in the air. Recommended mounting height for Nitrogen Dioxide (NO2) gas detector is 0.2 meter above the floor.

According in garages are concentrations expected less 1%VOL and because of thermal an convection of gas the spreading is at whole area.

What is the gas sensor (cell) life time for CO gas detectors and NO2 gas detectors?

CO gas sensor (cell) life expectancy is 5 years, normal operation environment.

NO2 gas sensor (cell) life expectancy is 2 years, normal operation environment.

If gas sensor (cell) is intensively exposed for fumes (gas) the life time is shorter.

If gas sensor (cell) is less exposed for fumes (gas) the life time can be longer.

Questions & Answers on Gases in F&G

What kind of substance is carbon monoxide?

A colourless, odourless, highly toxic gas that is formed whenever incomplete combustion of carbon, or carbon-containing compounds occurs. In our immediate environment it frequently is given off by industrial gas burners, and as it can be found in automotive exhaust or cigarette smoke it tends to accumulate in poorly ventilated places like congested road tunnels or bars at levels approaching or even exceeding the 50ppm threshold.

What are the symptoms that carbon monoxide has been inhaled?

CO depletes the oxygen in the blood hemoglobin leading to such typical symptoms as headaches, nausea, dizziness, etc.

symptoms of carbon monoxide

What kind of substance is hydrogen sulphide?

H2S is a colourless, toxic, flammable gas that occurs naturally in volcanic vapours, hot springs; and it often is generated through the hydrolysis of sulphide salts especially where bacteria break down organic matter in the absence of oxygen, e.g. in swamps, sewers, rivers, harbours, etc. It also occurs as a manmade by-product in such industrial facilities as chemical plants, paper mills, oil refineries, etc.

What are the symptoms that hydrogen sulphide has been inhaled?

H2S is absorbed into the bloodstream, and transmitted to the nervous system via the lungs, Low concentrations are oxidised in the blood and quickly become harmless; high concentrations have a sweetish aroma and a neurotoxic effect, irritating the mucous membranes in the nose, throat, eyes; may cause subacute poisoning or affect the olfactory nerve to the point of losing one’s sense of smell. Basically, hydrogen sulphide is one of the more common pungent odour-emitting and discomfort-causing substances.

symptoms of hydrogen sulphide

What kind of substance is ammonia?

It is given off in the biodegrading process by microbes (in nature), and as a byproduct of seafood processing. Besides being a common synthetically produced inorganic component of nitric acid and fertiliser, it also has a broad range of other industrial uses. Since, ammonia does not harm the ozone layer, it has increasingly been coming into use as a refrigerator coolant.

What are the symptoms that ammonia has been inhaled?

Ammonia is one of the typical, malodourous substances, which cause discomfort. Inhalation of high concentrations is liable to cause pulmonary oedema. Contact with the skin or mucous membranes causes irritation that may penetrate as far as the inner tissue. When the eyes come into contact with high ammonia concentrations, visual impairment may result.

symptoms of ammonia

What kind of substance is carbon dioxide (CO2)?

Generally carbon dioxide is generated during the respiratory process of animals and plants and when microbes break down organic or when carbon materials combust. It is necessary for the process of photosynthesis in plants. In recent years the amount of CO2 has been increasing, and is becoming a serious factor contributing to global warming, the “greenhouse effect”.

What are the symptoms that carbon dioxide has been inhaled?

Although, it is extremely rare for weak carbon dioxide poisoning to have any ill effects, high concentrations can cause carbon dioxide narcosis, and in extreme cases even be lethal.

symptoms of carbon dioxide

What kind of substance is oxygen?

Oxygen, the most abundant naturally occurring gas, is discharged into the atmosphere through the process of plant photosynthesis. It is consumed during the respiration process of flora and fauna, photosynthesis in plants, as ell as combustion processes. The oxygen content in air is about 21%, in water 88.8%, and in the human body it is about 65%.

What are the symptoms of extreme oxygen deficiency?

Not enough oxygen in the ambient air can be fatal, causing hypoxia (deprivation of an adequate oxygen supply for the body. On the other hand, excessive oxygen in the air poses a fire hazard as it lowers the combustion temperature of flammable materials, and it serves as an accelerant as well.

symptoms of extreme oxygen deficiency

What kind of substance is sulphur dioxide (SO2)?

Sulphur dioxide gas (sometimes also called sulphurous acid gas) has a strong pungent smell. It is produced industrially, by roasting pyrites or sulphur in the presence of air. Moreover, it occurs naturally in volcanic gas and it is a byproduct of fossil fuel (oil, coal, etc.) combustion that is a cause of air pollution.

What are the symptoms that sulphur dioxide has been inhaled?

High concentrations cause severe irritation of eyes, nose, and throat. When it dissolves in the water content of the skin, a corrosive acid (sulphurous acid) is formed. Prolonged exposure can cause glottal and pulmonary oedema seriously affecting the respiratory process.

symptoms of sulphur dioxide

What kind of substance is ozone?

Ozone (O3) is actually a triatomic allotrope of oxygen: one ozone molecule contains one (radical) oxygen atom more than diatomic O2 (from which it can also be formed by action of high energy electromagnetic radiation).

Paradoxically, although the ozone layer in the atmosphere (approximate O3 concentration: 0.005ppm) protects the earth from the sun’s ultraviolet light, at ground level in coastal regions (where ultraviolet light is particularly intense) 0.05ppm of ozone can be found. Because ozone is highly oxidisable, it is used for sterilization, disinfection, bleaching, and as an oxidant and such in organic synthesis.

How does ozone affect the human body?

When 0.1ppm of ozone are inhaled for two hours, the lung capacity can decrease by 20% or so. Headaches or bronchitis may result when a concentration of 1ppm is inhaled for six hours. In experiments, when laboratory rats inhaled 10ppm, they suffered pulmonary oedema and died which indicates a comparable degree of toxicity as phosgene, which is widely-acknowledged as a highly toxic gas.

What are the common methods for analysing / measuring ozone?

A typical analysis method involves the use of a potassium iodide solution to absorb ozone and determine the concentration by absorptiometry. Other practical methods entail the use of instruments for measuring ultraviolet (UV) light absorption, chemiluminescence, controlled potential electrolysis (CPE), or galvanic cells.

What kind of substance is methane?

Methane, a colourless and odourless gas has long been known as a chief ingredient of swamp gas. Methane gas is formed as organic matter such as cellulose decays in the mud of marshes or other wetlands. It is flammable and when mixed with air can become volatile enough to explode. It often accumulates in underground passageways/conduits (including mine shafts and sewers) where it can pose a serious explosion hazard.

How does methane affect the human body?

Methane in itself is harmless, but when its concentration rises, the oxygen concentration falls which can cause hypoxia. It also poses an explosion hazard, as it is easily ignitable; (explosive hazard range 5.0-15.0%)

Where is nitrogen oxides measurement mainly conducted?

Nitrogen oxides (NOx) is a generic term for any of a number of different oxygen compounds (known as oxides) of nitrogen that are given off during combustion, including nitrogen monoxide (NO) and nitrogen dioxide (NO2). Today, their primary sources include automobile exhaust and factory emissions; although heating and cooking fumes do their part as well.

What kind of substance is nitrogen oxides?

One of the most common nitrogen oxides is nitrogen monoxide (NO) which most commonly is generated during high temperature combustion; however, when nitrogen monoxide is discharged into the atmosphere, it oxidises into nitrogen dioxide (NO2). When this process occurs under certain meteorological conditions where the interaction of ultraviolet light as well as the presence of hydrocarbons come into play, photochemical smog is created. To regulate nitrogen dioxide emissions (which are inherently more toxic and hazardous than NO), a number of environmental standards are in place.

How do nitrogen oxides affect the human body?

It is extremely rare for nitrogen monoxide (NO) or nitrogen dioxide (NO2) to be present without the other. Nitrogen dioxide is toxic and, in high concentrations, strongly irritates eyes, nose, and throat, causing a cough or even pharyngalgia at times, dizziness, headaches, or nausea at times. If a large quantity is inhaled, the lips turn blue 5-10 hours later, and cyanosis may occur in addition to pulmonary oedema. Even low concentrations generally becomes a problem and raises chronic bronchitis, gastrointestinal dysfunctions, teeth problems and sleep disturbance as chronic symptoms. In addition, it weakens the body’s immune system.

What kind of substance is trichloroethylene?

Trichloroethylene is very volatile and in its liquid state at normal temperatures. It is commonly used to degrease metal machine parts and when it seeps underground it sometimes contaminates wells or groundwater which is increasingly becoming a problem in recent years.

What kind of substance is chlorine?

Chlorine, a highly caustic gas with a strong irritating odour, does not occur naturally as such. Chlorine-based solvents such as chloroethylene or organochlorine and inorganic chlorine compounds are widely used as source material in a broad range of products and processes including paper bleach, pulp fiber, medical supplies, pesticides, pigment dye, mineral ore refinement and metal processing. Moreover, urban drinking water which we use every day contains chlorine as a disinfectant to eliminate bacteria.

How does chlorine affect the human body?

Inflammation is caused when chlorine comes into contact with the skin. When inhaled, causes coughing and dyspnea, and even death. Chronic symptoms include bronchitis, inflammation of nasal mucous membranes.

chlorine effects

What kind of substance is hydrogen cyanide?

Also known as hydrocyanic or prussic acid, hydrogen cyanide is a clear colourless gas with a faintly bitter almond-like odour that is volatile in its liquid state with a boiling point of 25.7ºC (78.26ºF) and a ignition point of 17.8ºC (64ºF). It is soluble in water and often used as an aqueous solution. Its vapour density is slightly less than air (0.947) and its LEL (lower explosion limit) is 5.6% and its UEL (upper explosion limit) is 40%. It is chiefly used as a source material for various organic compounds such as acrylonitrile, or for potassium cyanide as well as in insecticides/pesticides, etc.

How does hydrogen cyanide affect the human body?

Hydrogen cyanide (HCN) is one of the most lethal poisons, being twice as toxic as potassium cyanide. It can be fatal not only when swallowed, but, even when it merely comes into contact with the skin. Characteristic of hydrogen cyanide poisoning is how quick it acts. It takes between a few seconds and 30 minutes maximum for a fatal dose (300ppm or more) to kill an adult. Hence, any emergency first aid (detox) measures must be immediately and swiftly initiated or it will be too late. When the gas is inhaled it may cause headaches, dizziness, ringing in the ears, or vomiting and in severe cases, unconsciousness, or even death.

The concentration and an illustration of action (In the case of gas inhalation)

Hydrogen cyanide effects

What kind of substance is arsenic?

Arsenic is a fairly common fragile crystalline metalloid ranging in colour from silver-white to black. It can be produced industrially through a chemical reaction using carbon to reduce arsenious acid in to its elements. All compounds containing arsenic are toxic and when they comes in contact with acid or acid vapour, a highly toxic gas (arsine) occurs. It is mainly used in insecticides, herbicides, desiccants, and in semiconductor fabrication.

How does arsenic affect the human body?

It frequently affects the function of the digestive organs, causing loss of appetite, convulsions, nausea, constipation or diarrhea, hepatic disorders, and in severe cases, blood may be vomited up or found in feces, leading to a state of collapse or shock, and in extreme cases may be fatal. Moreover, it is considered to have carcinogenic effects on skin, lungs, and liver, too.

What kind of substance is a hydrogen peroxide?

Hydrogen peroxide is a clear, unscented and oily liquid that is water insoluble. It can be extracted with mercury oxide after dissolving α-ethyl anthraquinone in an industrial solvent and oxidising in a (redox reaction). In general, hydrogen peroxide is commercially available as a 30% solution. It also interacts as a reducing agent and a powerful oxidiser. When metal catalysts in fine particle form (e.g. copper, silver or platinum) trigger decomposition, high concentrations of oxygen/steam are produced that can combust explosively. Hence, hydrogen peroxide is used in 3% solutions not only as a disinfectant, or a bleaching agent for paper, pulp, and natural fibers, but, also as an oxidiser, sterilizer, reducing agent, and even as liquid rocket fuel.

How does it affect the human body?

It is highly caustic to skin and mucous membranes, while a 30% solution can cause severe inflammation of eyes and skin upon contact. It is commonly known, that in work environments where hydrogen peroxide is in use, exposure to the vapour can have a bleaching effect on hair. If larger quantities are ingested, gastritis and acute toxic effects such as esophagitis, and chronic toxicity symptoms are likely.

What kind of substance is hydrogen chloride?

HCl is a strongly pungent, colourless to slightly yellowish gas. In nature it occurs in volcanic gas and in the human body’s gastric juices as hydrochloric acid (HCl dissolved in water). It can be produced by the direct reaction of hydrogen and chlorine, or in a laboratory by dripping concentrated hydrochloric acid into a strong sulphuric acid solution. Generally it is marketed as hydrochloric acid in 35-37% concentrations. Its main uses are in the production of: medical supplies, pigment dye intermediates, inorganic chlorides, chloroethylene (i.e. vinyl chloride), methyl chloride as well as etchants (i.e. etching solutions).

How does hydrogen chloride affect the human body?

Contact with eyes or skin causes inflammation. When inhaled, it irritates mucous membranes in throat or nose, and causes coughing. When substantial amounts are inhaled it can cause pulmonary oedema and even death.

hydrogen chloride effects

What kind of substance is sulphuric acid?

One common production method involves burning sulphur or pyrites (usually iron sulphide), to obtain sulphur dioxide which is then oxidised, and dissolved in water. Sulphuric acid is one of the most common basic materials, and it is used in fertiliser, pigment dye, petroleum refining, organic compound production, as well as myriad other uses in the chemical industry.

How does sulphuric acid affect the human body?

Contact with the skin can cause dermal dehydration or corrosion and severe acid burns. If its vapour is inhaled for longer periods, tooth erosion, damage to respiratory organs, and even pneumonia or pulmonary oedema can ensue. Extended contact with the eyes can cause blindness.

sulphuric acid effects

What kind of substance is ethylene oxide?

It is a colourless highly water-soluble substance that is in its gaseous state at normal (room) temperature and has an ether-like odour. It is frequently used in organic compound formation, as a colourant, surface-active agent (surfactant), as well as for sterilizing medical instruments. Its explosive range is very wide with an LEL (lower explosive limit) of 3.0% and a UEL (upper explosive limit) of 100%. With a very low ignition point of -17.8ºC (0ºF), its vapour is volatile enough to explode even in the absence of air / oxygen. Moreover, as there are indications that it may be a carcinogen, the Japan Society for Occupational Health and the ACGIH stipulate a TLV (Threshold Limit Value) and administrative concentration threshold of 1ppm. In addition, in Japan Air Pollution Control Law it is included among the “Substances Requiring Priority Action” as it is thought to pose a significant health risk among the hazardous air contaminants.

How is ethylene oxide measured ?

As part of th leak check protocol for comparatively high concentrations, it is measured with (flammable) gas detector alarms, gas detector tubes, etc. To measure ethylene oxide in ambient air, various contaminant measurement manuals recommend solid-phase sampling involving solvent-extraction gas chromatographic mass spectrometry. In general, working environment standards prescribe gas chromatography of substances in solid state.

What kind of gas is chlorine dioxide?

It has a pungent odor, is heavier than air, and is red to yellow in colour. It readily dissolves in water (Solubility: 0.8 g/100 ml at 20ºC), and is often used even as a solution in water. Chlorine dioxide itself is incombustible, but has extremely high oxidizability, and poses a danger of fire or explosion due to contact with combustible matter or reductive matter, or as a result of exposure to heat, sunlight, impact, or sparks. Representative industrial applications include disinfectant, which utilizes this powerful oxidation reaction, and also bleaching agent for fibers, pulp and foodstuffs. When using chlorine-base bleaching agent or detergent, for example, it is necessary to take care because chlorine dioxide may be inadvertently generated.

How does chlorine dioxide affect the human body?

Chlorine dioxide has even greater irritability and toxicity than chlorine, and seriously irritates the eyes, skin and windpipe. It has been reported that at a concentration of 5 ppm, chlorine dioxide exhibits definite irritability, while at 20 ppm, it can result in death in a short time, and even at 0.1 ppm, chronic exposure to chlorine dioxide may result in various symptoms such as inflammation of the windpipe. Acute symptoms such as pulmonary edema may occur after several hours of exposure, so when there is acute exposure it is essential to obtain a diagnosis of a physician and also subsequent follow-up.

What kind of substance is mercury?

Mercury is a liquid that shines silver-white. It is the only metal that is a liquid at normal temperature. The specific gravity of mercury is an extremely high value of 13.6, making it very heavy. On the other hand, it readily evaporates, and easily forms amalgams with a variety of metals. Mercury is a highly toxic substance as is also evidenced by reports concerning poisoning due to methyl mercury. However, it is widely used not only as an industrial reagent, but also in measuring instruments such as thermometres, and also in agriculture, batteries (at present, it is used only in button batteries), and in drugs and medicines. In days gone by, if you cut or grazed yourself, the first thing that you did was apply mercurochrome to the wound. Previously, mercurochrome was kept in all homes as a household antiseptic, but nowadays it is virtually no longer used because it uses mercury (its use is not prohibited, and if you go to a chemist’s shop you can still purchase it).

How does mercury affect the human body?

If mercury vapour is inhaled, various psychological symptoms such as loss of appetite, a headache, heaviness of the head, general malaise, minor trembling, and insomnia are likely to occur. Mercury is also absorbed through the skin. The allowable concentration of mercury stipulated by the Japan Association of Industrial Health is 0.025 mg/m3 for mercury vapour. The value stipulated by TLV (TWA) of ACGIH, for both a single element and an inorganic compound, is 0.025 mg/m3, and the value at the control temperature stipulated by the Ministry of Health, Labour and Welfare is 0.05 mg/m3.

What kind of substance is tetrachloroethylene?

This substance is also called perchloroethylene. It is a volatile substance which is colourless and emits a characteristic odor. Tetrachloroethylene is noncombustible and easily dissolves oil, so it is used as a solvent for dry cleaning and also for degreasing and washing metal parts. Previously, tetrachloroethylene was covered by the Ordinance On Prevention of Organic Solvent Poisoning. In 2014, however, this ordinance was revised to become the Ordinance on Prevention of Hazards due to Specified Chemical Substances. As a result, tetrachloroethylene came to be ranked as a “special organic solvent, etc.” among type 2 substances of specific chemical substances. It also became a special controlled substance, and it became mandatory to devise measures based on its carcinogenicity. In addition, according to the partial revision of the Work Environment Evaluation Criteria, the control concentration will be reduced from 50 ppm to 25 ppm commencing October 1, 2016.

References : gastec.co.jp

Fire and Gas System Interview Questions & Answers


What is a fire alarm system?

Typically, a fire alarm system is made up of the following components:

  • Initiating devices, capable of placing the system in the alarm state. These can be photoelectric smoke and heat detectors, ionization smoke detectors, heat detectors, in-duct smoke detectors, manually operated pull stations and sprinkler water flow sensors.
  • Indicating appliances, whose purpose is to announce building occupants or at a remote location when the system enters the alarm state, such as horns, strobe lights, chimes, bells, or combination units. They are also available in weatherproof and hazardous location versions.
  • A control panel, containing programming and operating electronics and user interface, is fed by standard branch-circuit wiring and contains replaceable circuit cards – one for each zone. This includes an alphanumeric display, showing the state of the system and providing troubleshooting information, and a touchpad so that onsite personnel can silence an alarm or trouble signal, reset the system following an event, and reprogram if necessary
  • Sealed batteries similar to emergency light batteries, but listed for fire alarm systems. These are usually 6V batteries wired in series to make up 24VDC for a power-limited system. The batteries can be contained in the control panel or in a separate enclosure. When AC power fails, the batteries take over with no interruption in fire protection. Of course, there is also a charger.
  • Auxiliary devices, including remote annunciators with LEDs showing the state of the system, an alarm silence switch, and visual LED indication of the zone from which a fire alarm is initiated. Electromagnetic door holders (floor- or wall-mounted) are available. In case of alarm, the magnet is de-energized, allowing the door to swing shut. Later, it is reopened manually.
  • Initiating devices are connected to the control panel by a 2- or 4-wire initiating device circuit. In the case of a power-limited system, 24VDC is applied to two wires going to a string of initiating devices, which are wired in parallel. Neither wire is grounded, and they are isolated from EMT or other raceways, which are grounded through the connector at the control panel. Polarity is also critical. This voltage is used to power the solid-state circuitry within each detector. It’s also used by the control panel to monitor the state (alarm or no alarm) of the initiating devices and zone wiring.

A typical fire alarm system has numerous initiating devices divided among separate zones – each connected via an initiating device circuit to a central control panel. The control panel performs supervisory functions over the initiating devices, indicating appliances, all associated field wiring, telephone ties, and its own internal wiring and circuit cards.

What is the main component of a fire alarm system?

The Fire Alarm Control Panel (FACP). The FACP should be located where it can be responded to as necessary either around the clock or during operating hours. This can be at building security headquarters, adjacent to a telephone switchboard or in a maintenance office – whichever location offers maximum coverage. It should also be positioned in a fairly central location because if the system goes into alarm, a person needs to be able to race to the location and verify fire status before the alarm is silenced.

How does a fire alarm system operate?

A fire alarm system operates in one of three (or more) states: normal, alarm, and trouble. The state is reported at all times on the alphanumeric display. If the system goes into alarm, the indicating appliances throughout the building go off. These could be very loud horns for some occupancies, or softer chimes in others, such as a nursing home.

The control panel monitors the initiating device circuits at all times for shorts and open wiring by means of the applied DC voltage. The initiating devices are normally open. In the event of a fire they become conductive at close to zero ohms. How, then, is it possible for the control panel to differentiate between a non-alarm state and an open wiring fault? This is accomplished by means of an end-of-line resistor.

The control panel also monitors the functionality of its own wiring and zone cards, and trouble is reported in the display.

fire alarm system operation

Another capability of the fire alarm system is to call out in case of alarm. Two dedicated phone lines are connected, and the system performs test calls periodically in accordance with programmed instructions. If either phone line won’t connect, the system goes into the trouble state, so repairs can be made.

The essence of a fire alarm system, as opposed to individual smoke detectors, even if they are wired to indicate in concert, is that it is supervised from a central location. The whole notion of supervision is critical. It does not mean that a person sits at the console and watches it at all times. What it means is that a supervisory voltage is applied to all circuitry, and current flow is monitored electronically to verify that equipment and wiring are intact.

If the system goes into alarm and won’t silence due to touchpad malfunction, for example, it can be disarmed after the zone is checked for fire by cutting off the power. First, unhook one side of the battery array, then unhook the black-white-green incoming power connector. If a fire alarm system is disabled, maintenance and security personnel should initiate fire patrols throughout the building. The telephone monitoring agency should be informed, and the insurance company contacted to verify that coverage is not voided.

What is Conventional Fire Alarm System ?

Traditional fire alarm panels installed prior to 1998 were conventional zone panels. In a zoned system, fire alarm devices in a common area or floor of a facility are connected to the same alarm initiating circuit. Each zone requires its own circuit conductor. This arrangement allows alarm annunciation to be reported by areas of the building to identify which device is in alarm. Conventional panels are often used in small facilities where a few zones can provide sufficient alarm annunciation.

What is Addressable Fire Alarm System ?

With the advent of microprocessors and digital electronics, addressable fire alarm control panels and devices have become more common than conventional systems for medium and large-sized facilities. They have become more cost effective in some small applications as well.

Addressable fire alarm systems use digital encoding and multiplex technology to more accurately identify alarm locations and device conditions. Each fire alarm device in a system is programmed with a unique address.

The fire alarm control panel is capable of communicating with a single address or a group of addresses depending on the functions required. The communication is often multiplexed over a common cable, sometimes referred to as the signaling line circuit (SLC). This arrangement significantly reduces the amount of cabling necessary to install the system. The communication channel allows two-way communication, thus enabling the fire alarm control panel to control as well as monitor fire alarm devices.

A significant component of addressable fire alarm system is the software programming necessary to make the system function correctly. The programming allows for flexible applications where you want to have specific control over the inputs and outputs.

The communication technologies employed in addressable systems allow for advanced features to accommodate sensitivity changes due to age and accumulation of dust prior to maintenance. These features are not available with the standard conventional system.

What are the Fire Alarm Devices ?

  • Smoke (particulate and aerosol)
  • Heat
  • Light Radiation
  • Fire detection devices are built to detect one or a combination of these components. While all components are necessary for a fire to exist, all components may not exist at a detectable threshold. Detectors will be selected that will detect the elements that may exist in a fire for the ambient conditions that are present. It also should be realized the similar non-fire components might exist in the same ambient conditions, which could cause unfavorable false alarm conditions.
  • Devices used for fire detection include smoke detectors, thermal detectors, flame detectors, fire-gas detectors, and other devices.
  • Smoke detectors sense visible or invisible particles of combustion generated by burning, smoldering, or the incipient stage of combustion. These devices fall into two categories — photoelectric and ionization.
  • Thermal detectors sense the high temperature or the temperature rise caused by a fire.
  • Flame detectors sense the radiation produced by a fire.
  • Fire-gas detectors sense the gases produced by a fire.
  • Other detectors sense some phenomenon other than smoke, thermal, flame, or fire-gas to detect a fire.

Explain about Ionization Smoke Detector ?

The ionization smoke detector is widely used. Its capability to detect smoke originating from fire is best utilized for clean-burning fires that produce small particles during combustion.

The ionization smoke detector consists of an alpha particle producing a radioactive source, a smoke chamber, and charged detector plates.

  • The alpha source causes the air within the smoke chamber to become ionized and conductive
  • As smoke particles enter the smoke chamber, the smoke particles attach themselves to the ionized air molecules and the air in the chamber becomes less conductive
  • When the air conductivity within the chamber drops below a predetermined level, the alarm is triggered

Advantages of Ionization Smoke Detectors:

  • Detects invisible products of combustion — It can detect fires that are in the incipient stage or detect other aerosol-type smoke products
  • Quick acting — Provides for earlier detection than other types of smoke detectors or thermal detectors
  • Disadvantages of Ionization Smoke Detectors:
  • May provide false detection if used where volatile solvents, conductive material dusts, or high humidity are present
  • Detects the presence of smoke only, not toxicity
  • Has a potential for high false alarm rate
  • Typical locations or hazards for ionization detection:
  • Clean rooms
  • Computer rooms
  • Mechanical air ducts
  • Locations where sensitive detection methods are needed

Explain about Photoelectric Smoke Detector ?

A photoelectric smoke detector is the most common smoke detector used today. It detects smoke by using either the principle of light obscuration or light scattering. Its capability to detect smoke originating from fire is best utilized for fires that produce large particles during combustion.

Spot type photoelectric smoke detectors using the light obscuration principle have a light emitting device, usually a light-emitting diode (LED), a smoke chamber, and a photosensitive device that receives the light directly from the light source and produces a monitored current.

Smoke that enters the smoke chamber reduces the intensity of tech light reaching the photosensitive device, which reduces the monitored current. When the intensity drops below a certain level, the sensor control circuitry detects a drop in the current produced by the photosensitive device. When the current falls below a preset threshold, the smoke alarm is triggered.

Spot type photoelectric smoke detectors that use the light scattering principle are constructed similarly to the detectors that use the light obscuration principle except that the photosensitive device is set so that it cannot see the light source directly. When smoke enters the chamber, the smoke particles reflect the light from the source into the photosensitive receiver. When sufficient light intensity is detected, the alarm is triggered.

Advantages of Photoelectric Smoke Detectors:

  • Sensitive to visual particles of smoke
  • Detects smoldering low heat fires
  • Provide early warning

Disadvantages of Photoelectric Smoke Detectors:

  • Early contamination by dust causing reduced sensitivity
  • Detects presence of smoke, not toxicity
  • Must be cleaned on a regular basis
  • Has a potential for high false alarm rate

Explain about Beam Detector ?

Beam detectors are line-type photoelectric detectors consisting of a separate light source and photosensitive receiver. These devices are usually installed in large open areas where there is an unobstructed line of sight between the light source and the receiver and where the use of spot-type detectors would be economically unfeasible due to the number of detectors required.

Advantages of Beam Smoke Detectors:

  • Cover a large area economically
  • Quick acting
  • Disadvantages of Beam Smoke Detectors:
  • Unobstructed LoS between the light source and the receiver
  • Correct alignment needs to be maintained
  • Typical locations or hazards for beam detectors:
  • High atriums
  • Manufacturing spaces

Explain about Air Sampling Smoke Detectors ?

For environments where detection of smoke is most critical, an air-sampling system provides the earliest possible detection. An air sampling or aspirating type fire detection system is a self-contained smoke detection package compromised of five primary components:

  • Air-sampling system
  • Aspiration system
  • Filter assembly
  • Detector
  • Control system

It uses a network of pipes to continuously draw air samples and direct them to a central smoke detector.

The system operates with a network of sampling pipes that extend into the protected area. The pipes are usually made of a thermoplastic material. An internal aspirator continuously draws air into the piping network. The systems use either a filter assembly or laser particle counting technology to filter out airborne dust and debris particles, which helps to eliminate false readings.

Typical locations or hazards for Air-Sampling smoke detectors:

  • Telecommunications areas
  • Computer rooms
  • Data centers
  • Hospitals
  • Clean room environments

Explain about Fixed Temperature Thermal Detectors?

Fixed Temperature

  • Fixed Temperature Thermal Detectors can respond to:
  • Fixed temperature limit
  • Rapid rate of change of the temperature in the protected area
  • Combination of these types of detection

Typical fixed temperature spot-type smoke detectors contain a bimetallic switch element that closes at a specified temperature limit. The switch is normally composed of two metals, each having a different temperature coefficient of expansion. As this bimetallic element heats the metal with higher coefficient of expansion, it causes the switch to bend or curve, closing the switch; thus indicating an alarm condition.

Line type thermal detectors are cables that detect heat along their entire length. A line type thermal detector may consist of two wires that are separated by an insulator. After the heat builds to a certain level the insulation melts, allowing the wires to touch and current to flow, initiating an alarm.

Bimetallic spot and coaxial style thermal detectors are self restoring. Fusible link and melting insulation types of line thermal detectors are not self-restoring.

Advantages of Fixed Thermal detection:

  • Lower cost than smoke detector units
  • More reliable than smoke detector units
  • Not affected by dusty or dirty environments
  • Minimal maintenance

Disadvantages of Fixed Thermal detection:

  • Slower to respond than smoke detectors
  • Will not detect products of combustion
  • Only suitable for protection of property

Explain about Rate of Rise Thermal Detectors?

Rate-of-Rise Thermal Detectors measure the rate at which the air temperature changes during a fire event. Measuring the change in temperature provides a faster alarm response than measuring the temperature level in a space.

The rate-of-rise detector measures the change in the temperature of the space through the use of a differential pressure switch. This switch contains an air chamber separated for the air in the ambient space by a flexible diaphragm. As air in the ambient space changes temperature, the air pressure increases, creating a differential pressure across the diaphragm.

The air chamber is constructed with a calibrated leak so that normal temperature and pressure fluctuations within the room space adjust across both sides of the diaphragm and will not cause the alarm contacts to close. During a fire, the air temperature rises at a rate faster than normal, causing an increase on the room side of the diaphragme diaphragm. The leak cannot compensate, and therefore the diaphragm moves and closes the detector contacts.

Combination rate-of-rise and fixed temperature thermal detectors are also manufactured and have both technologies built in.

Advantages of Rate-of-Rise Thermal detection:

  • Responds faster than the fixed temperature detector
  • Not affected by dusty or dirty environments
  • More reliable than smoke detector units
  • Less expensive than smoke detector units
  • Minimal maintenance

Disadvantages of Rate-of-Rise Thermal detection:

  • Slower to respond than smoke detectors
  • Will not detect products of combustion
  • Only suitable for protection of property

Explain about Rate Compensated Thermal Detectors?

Rate-compensated thermal detectors are devices that are designed to activate at a predetermined temperature in a space regardless of the rate at which the temperature in the space increases. This is accomplished by compensating for the thermal lag between the room temperature and the interior of the device.

Construction consists of an outer metal tube that expands at a fixed rate. Within this tube, alarm contacts close when a certain expansion distance is reached, but this expansion is opposed by another metal device.

At a slow rate-of-rise in temperature, the outer tube expands drawing the contacts closer together. The inner metal device exerts a counter force, keeping the contacts separated until the entire device has been heated to its rated temperature.

At a rapid rate-of-rise in temperature, the outer tube expands faster than the inner device can compensate. Therefore, the alarm contacts close when the entire device has been heated to a lower level, thus compensating for thermal lag.

Advantages of Rate Compensated Thermal detectors:

  • Responds accurately and positively to fire threats
  • Virtually eliminates false alarms
  • Not affected by dusty or dirty environments
  • More reliable than a smoke detector
  • Less expensive than smoke detector units
  • Minimal maintenance

Disadvantages of Rate Compensated Thermal detectors:

  • Slower to respond than smoke detectors
  • Will not detect products of combustion
  • Only suitable for protection of property

Explain about Flame Detector ?

Flame detectors are used to detect the light radiation component of a fire. Typical detectors of this type detect the wavelength of either IR or UV or a combination of the two. These detectors are extremely fast acting and are used in areas where rapidly occurring fires or explosions could occur.

Advantages of Flame Detection:

Disadvantages of Flame Detection:

  • Narrow field of vision
  • Expensive
  • Requires unobstructed field of view
  • Difficult to maintain

Typical Uses:

  • Fuel loading docks
  • Industrial process spaces
  • Other hazardous areas where a fast developing fire could occur

Explain about Fire-Gas Detector ?

These detectors respond to the various gases produced during the combustion process.

  • Carbon monoxide
  • Carbon dioxide
  • Steam
  • Other elements

The Fire-Gas detector employs two types of technology to predict the fire. One method uses a semiconductor material that changes the metals conducting potential in a fire situation. The other method uses a catalytic element encased in an aluminum bead.

Advantages of Fire-Gas Detection:

  • Detects products of combustion
  • Sensitive enough to detect levels of gases produced between the occurrences of detectable particulate levels and detectable heat levels
  • Detects gases prior to reaching lethal levels

Disadvantages of Fire-Gas Detection:

  • Can be prone to false alarms
  • Must be mounted at a low level, leaving it susceptible to damage
  • Can be poisoned
  • Not suitable for areas where CO and CO2 and produced as part of the functions within the area
  • Cannot be considered as a universal replacement for smoke and/or thermal detectors
  • High cost

What is carbon monoxide?

Carbon monoxide is a colorless, odorless gas that is produced by certain gas-powered appliances and engines. If a gas leak occurs, carbon monoxide can build up in certain areas. If a person is exposed to the gas for an extended period of time, he or she can suffer serious complications. For this reason, many residences and commercial buildings have carbon monoxide detectors, similar to smoke detectors, installed to prevent injury to occupants. Fire safety inspectors check safety equipment and alarms to ensure that they are in compliance with codes and regulations and will keep people and property safe in the event of a fire or other accident.

What is a preventable response?

Sometimes, firefighters are called to buildings because of a malfunction in the automatic fire alarm system or because the system is triggered by something other than a fire. Since a false alarm, also known as a preventable response, causes such a drain on resources, city fire departments may fine the owners of buildings for these preventable false alarms.

These fees are meant to encourage building owners to keep their systems in top working order through regular inspections by a certified inspection service. They also help fire departments increase their resources for responses to actual emergencies.

With regular service and maintenance, you can prevent false alarms with your fire prevention systems.

What is a flow test ?

A flow test is a procedure performed by fire safety inspectors to ensure that fire sprinkler systems are working properly. This test is required in order to make sure that a fire sprinkler system will be able to supply enough water during a fire. Even if primary water supply systems fail during a fire, fire sprinkler systems should still be able to deliver enough water to contain a fire.

What is an NFPA standard?

The NFPA is the National Fire Protection Association, a fire prevention and safety organization. The NFPA creates and publishes fire safety codes and standards to reduce the risk of fire. The NFPA has standards for each building’s sprinkler systems and alarm systems. Fire safety inspectors will check sprinkler heads, pipes, flow water, pressure, valves, smoke detectors, pull stations, and batteries so that they comply with these codes and standards. Without these standards and codes, buildings would be at a high risk of fire danger.

How do we use a fire extinguisher?

Whether you live in a high rise apartment or work in an industrial setting, it is important to understand how to operate a fire extinguisher. Most occupational settings with high fire risks should go through safety trainings to show employees how to properly use a fire extinguisher. Even if you have had no proper training, you can learn the “PASS” method:

  • P. Pull the pin.
  • A. Aim the extinguisher at the base of the fire.
  • S. Squeeze the lever slowly and steadily.
  • S. Sweep the extinguisher from side to side to cover the whole area.

What are the different types of fire extinguishers?

There exist several different types of fire extinguishers, each designed to fight particular types of fires. They are organized into different classes of fires, including:

  • Class A. Paper, wood, or plastic fires
  • Class B. Fires from flammable liquids, such as oil or gasoline
  • Class C. Electrical fires
  • Class D: Fires from combustible metals, such as sodium or magnesium (often in laboratory settings)

Water cannot put out all fires – in fact, it can make some fires even worse. Your workplace should have the proper type of fire extinguisher installed to help fight the type of fire most likely to occur.

How are fires classified?

Depending on the agent that fuels the fire, fires are classified into different categories: Class A (regular combustibles), Class B (flammable gasses and liquids), Class C (electrical equipment), Class D (combustible metals), and Class K (cooking fats and oils). Different fire extinguishers are specially designed to fight different classes of fires. Fire safety is absolutely essential for protecting both human life and property investments.

How does a fire sprinkler system work?

Each sprinkler head is held closed by a small piece of heat-sensitive material. This piece acts as a plug to prevent water from flowing at normal temperatures. When heated by a fire, the sprinkler heads near the fire are activated and release water to put out the fire. To keep the pressure steady and avoid overwhelming local water suppliers, the entire system is powered by a fire pump, which pumps water at large volumes from a separate water source.

What is a fire pump?

A fire pump is an integral part of fire sprinkler protection systems in large buildings. Local water systems do not have the capacity to provide a steady stream of water throughout a fire sprinkler system in the event of a fire. The fire pump is connected to a separate source of water and has the power to pump large volumes of water, even to the top floor of a very tall building, in a continuous flow. Fire pumps require regular inspection and maintenance in order to ensure that the entire sprinkler system will function properly in the event of a fire.

What are the different types of fire sprinkler systems?

Different types of fire sprinkler systems have been designed to meet the optimum needs of your commercial building, no matter what your business or industry. Types of fire sprinkler systems include wet pipe systems, dry pipe systems, deluge systems, pre-action systems, foam water sprinkler systems, and water spray systems. Each type of system has its own set of advantages and disadvantages. An Austin fire safety professional from Ace Fire Equipment can further explain the differences and help you make a decision on which fire sprinkler systems is best for your building.

What is arson?

If a person intentionally sets a fire to a structure, they can be charged with the crime of arson. Businesses and restaurants, as well as residential buildings, are all at risk for arson.

What is a clean agent?

A clean agent is a fire-suppressing chemical in a gaseous form that will not harm electrical equipment or other objects that are easily damaged by water. Clean agents are also easier to clean up than other types of fire suppression systems. A clean agent fire suppression system is a good option for use in areas that can be harmed by water or other types of fire suppression chemicals.

What is active fire protection?

Active fire protection is a method which uses automatic or manual systems to detect and suppress fires. Active fire protection includes fire suppression efforts with fire extinguishers, sprinkler systems, and fire detection equipment such as smoke alarms. Any active fire suppression system must be properly installed and maintained to comply with local building and fire codes.

What is a HazMat Operations certification?

HazMat is an abbreviation of “hazardous materials.” A HazMat Operations certificate shows that we have had the special training necessary to recognize hazardous materials and dangerous goods. It is necessary for those working with water lines and fire prevention systems to have a complete understanding of hazardous materials and how to protect nearby people, property, and the environment from the effects of exposure.

References :

  • fieldsfire.com
  • currenttechnologies.ca
  • acefireequipment.com

PLC Program for Alarm Indication in Process


This is PLC Program for Alarm indication in process.

Problem Description

In many industries there are lots of machines which are performing many tasks automatically. There are many sensors and components used in system or process. Sometimes operator may not be identify the problems of machine or system by visual observations. And also sometimes there will be a chance that machine stops working due to some problem in it.

Problem Diagram

PLC Program for Alarm Indication in Process

Problem Solution

We can solve this problem by adding alarms in system or process. Alarms are added to alert operator to monitor that machine/process about to cross its limit values or already crossed the limit. Alarms are indicated to the operator by annunciator or horns, and lights of different colours on the panel. (For example, green lights meant OK, Yellow meant not OK, and Red meant BAD.)

The purpose of alarms is to use automation to help human operators as they monitor and control processes, and alert them regarding abnormal situations of the plant. Incoming process signals are continuously monitored, and if the value of a given signal moves into an abnormal condition, a visual and/or audio alarm informs the operator regarding the situation.

We can configure alarms for system by different ways, such as MIMIC, indication lamps on panel board, SCADA, HMI etc.

For our problem discussions, we considered one simple system and configure alarms for the system. For example consider one filling and discharging process and in this system we want to consider some alarms, we will show alarm by using lamps on panel board.

For example, consider following alarms for our system,

  • Emergency stop pressed
  • Feed valve open error
  • Feed valve close error
  • Discharge valve open error
  • Discharge valve close error

Here all are errors so we take all red color indication as shown in above figure.


Here is PLC program for Alarm indication in process.

List of Inputs/Outputs

Inputs List:-

  • Cycle START=I0.0
  • Cycle STOP= I0.1
  • Low Level Switch, LL=I0.2
  • High Level Switch, LH=I0.3
  • Feed VLV open LS=I0.4
  • Feed VLV close LS=I0.5
  • Disc. VLV open LS=I0.6
  • Disc. VLV close LS=I0.7
  • Emergency STOP=I1.0
  • RESET=I1.1

Output List:-

  • Cycle ON=Q0.0
  • Feed valve=Q0.1
  • Disc valve=Q0.2
  • BUZZER=Q0.3
  • Emergency STOP pressed= Q0.4 (Indication lamp)
  • Feed VLV open error= Q0.5 (Indication lamp)
  • Feed VLV close error=Q0.6 (Indication lamp)
  • Disc VLV open error=Q0.7 (Indication lamp)
  • Disc VLV close error=Q1.0 (Indication lamp)

Ladder diagram for Alarm indication in process.

Program Description

In this application, we have used Siemens S7-300 PLC and TIA Portal Software for programming.

Network 1: In network 1, we used latching circuit for cycle ON (Q0.0) output. It can be started by pressing cycle START PB (I0.0) and STOP by pressing STOP PB (I0.1).

When cycle will be START then system checks level of the tank. If tank level is low then the feeding process will start and if tank level reaches high then Discharge cycle will START.

Network2: When tank reaches low level then LL (I0.2) will be activated and feeding cycle will be ON. Here we have taken NC contact of LH (I0.3) so when PLC will detect high level then it will STOP feeding cycle.

Network 3: When tank reaches high level then LH (I0.3) will be activated and discharging cycle will be ON. Here we have taken NC contact of LL (I0.2) so when PLC will detect low level then it will STOP discharge cycle.

Network 4: When system receivies Emergency STOP (I1.0) input then it will activate the Emergency STOP pressed output (Q0.4) and alarm indication will be provded to the operator.

Network 5: In this network we have configured feed VLV open error alarm (Q0.5), when feed valve is ON and Feed VLV open LS (I0.4) is not detected then timer will START and after 5s Feed VLV open error alarm is ON (Q0.5).

Network 6: In this network we have configured feed VLV CLOSE error alarm (Q0.6), when feed valve is CLOSE and Feed VLV CLOSE LS (I0.5) is not detected then timer will START and after 5s Feed VLV CLOSE error alarm is ON (Q0.6).

Network 7: In this network we have configured Disc VLV OPEN error alarm (Q0.7), when disc valve is ON and disc VLV OPEN LS (I0.6) is not detected then timer will START and after 5s disc VLV OPEN error alarm is ON (Q0.7).

Network 8: In this network we have configured Disc VLV CLOSE error alarm (Q1.0), when disc valve is CLOSE and disc VLV CLOSE LS (I0.7) is not detected then timer will start and after 5s disc VLV close error alarm is ON (Q1.0).

Network 9: In this network we have configured BUZZER for all alarms, when alarm detected then BUZZER (Q0.3) will be activated and it can be RESET by pressing RESET (I1.1).

Network 10: Operator can reset the BUZZER by pressing RESET (I1.0)

Test Cases

PLC Program for Alarm Indication

Note : The above PLC Logic provided for basic idea about application of PLC in Alarm Indication of a Process. The Logic is limited and not complete application.

Article by
Bhavesh Diyodara

Flow Transmitters Questions and Answers


What is CFM, SCFM, ACFM, Am³/hr and N m³/hr?

  • CFM is a unit of flow rate (cubic feet per minute)
  • SCFM is a unit of flow rate (Standard Cubic Feet per Minute) at STP condition i.e. standard temperature 60º F and standard pressure 14.69 A PSI.
  • ACFM (Actual Cubic Feet per Minute) is the actual flow at the operating temperature and pressure conditions.
  • Am³/hr (Actual Cubic Meter per hour) is the actual flow at the operating temperature and pressure conditions.
  • Nm³/hr (Normal Cubic Meter per hour) is normalized value of flow at NTP conditions i.e. flow at Normal Temperature 0º C and Normal Pressure 101.32 kPa condition.

Note : STP/NTP conditions are decided by different organizations/authorities as per their specifications.

Why back pressure is necessary?

When measuring liquids, back pressure in the flow line should be sufficient to prevent cavitation. Cavitation occurs due to pressure drop at the obstruction in the flow line. Due to pressure drop, bubbles are formed and are driven to the further locations in the flow line where they break and erode the parts of flow line.

To avoid such cavitations, the back pressure in the line must be always greater than the vapor pressure of the fluid. To maintain back pressure in the line, larger pumping force is required.

In case of water and liquids of similar vapor pressure, required back pressure is approximately 1 kg/cm² at velocity of 6 meter/second. When there is no back pressure in the pipeline, it can be created by placing a partially closed valve on the downstream side of the flow meter.

What is Vortex Flow meter Principle ?

Whenever an obstacle is placed in a flowing fluid, vortices are generated alternately on both sides of the obstacle. The frequency of vortex generation is directly proportional to the velocity of the fluid and is independent of all other parameters.


F α V — Frequency is directly proportional to velocity.
F = KV — Frequency gives inference of velocity.


F = Frequency of Vortex Generation
V = Velocity of Fluid
K = Proportionality Constant

Vortex Flow meter Principle


Flow Rate (M3/Hr) = Area of Pipe in M2 x Velocity of Fluid in M/sec x 3600 seconds

Why upstream and downstream straight length is required?

Flow Meter accuracy is guaranteed for a fully developed flow profile in the pipeline at the installed location. Normally from flow disturbance point, flow is developed after a distance of about 20D or more. Hence minimum upstream straight length should be 20D for normal pipelines.

Minimum downstream straight length should be 5D from the flow meter to avoid disturbances in the flow.

Can a differential pressure flowmeter handle turbulent flow?

Yes; though meters are unidirectional a straight run of tubing or pipe is not required.

What are the advantages of using a variable area flowmeter?

Inexpensive somewhat self-cleaning no power required available in different materials for chemical compatibility Low and constant pressure losses Suitable for very low flow rates Rangeability 10:1 Capable of measuring fluids of varying density and viscosity (compensation given by float design).

Must a rotameter be mounted vertically?

Generally, rotameters must be mounted vertically, because the float must center itself in the fluid stream. At high flow rates, the float assumes a position towards the tip of the metering tube and at low flow rates positions itself lower in the tube. Some of the rotameters have spring loaded floats and therefore may be mounted in any orientation.

Can we use a rotameter in a vacuum application or with back pressure?

Yes, but if you have a valve, it must be placed at the outlet (top of the flowmeter). This is done by inverting the tube inside the frame, and then turning over the frame. At this position, the tube should read correctly from the original perspective and the valve should be at the outlet, or top of the flowmeter. This allows for proper control of the vacuum.

What is the difference between correlated and direct reading rotameters?

A direct reading flowmeter indicates the flow rate on its scale in specific engineering units (e.g. ml/min or scfh). Direct reading scales are designed for a specific gas or liquid at a given temperature and pressure. While it is more convenient than a correlated flowmeter, a direct reading flowmeter is less accurate and limited in its applications.

A correlated flowmeter is scaled along either a 65mm or a 150mm length, from which a reading is taken. The reading is then compared to a correlation table for a specific gas or liquid. This will give the actual flow in engineering units. One correlated flowmeter can be used with a variety of fluids or gases.

What are Multiphase Flow Meters?

Multiphase Flow Meters (MPFM) are devices used to measure the individual oil, water and gas flow rates in a multiphase flow. The term MPFM is used to define also the metering of wet gas streams (i.e. multiphase flow where the gas content is very high).

A multiphase flow meter is a device used to measure the individual phase flow rates of constituent phases in a given flow (for example in oil and gas industry) where oil, water and gas mixtures are initially co-mingled together during the oil production processes

Why is a Pressure Transmitter Installed Upstream of a Flow Transmitter?

Upstream of a flow control valve a pressure transmitter is installed to measure the operating pressure.

At times it is used for computing the true flow against the designed pressure.

Downstream of the control valve the pressure changes as the control valve open and closes.

Differential Pressure Flow meter Accuracy & Rangeability ?

Performance of a head-type flowmeter installation is a function of the

  • precision of the flow element and
  • the accuracy of the d/p cell

On average, flow element precision is expressed in percentage of actual reading terms, whereas d/p cell accuracy is stated as a percentage of calibrated span.

A d/p cell typically provides accuracy of ±0.2% of the calibrated span. With no detrimental effect on accuracy, rangeability of a flowmeter can be extra enhanced by employing several d/p flowmeters in parallel runs.

How Hot Wire Anemometer Works?

The hot-wire anemometer, principally used in gas flow measurement, consists of an electrically
heated, fine platinum wire which is immersed into the flow.

As the fluid velocity increases, the rate of heat flow from the heated wire to the flow stream increases. Thus, a cooling effect on the wire electrode occurs, causing its electrical resistance to change.

In a constant-current anemometer, the fluid velocity is determined from a measurement of the resulting change in wire resistance.

In a constant-resistance anemometer, fluid velocity is determined from the current needed to maintain a constant wire temperature and, thus, the resistance constant

Explain about Orifice Performance ?

Principally, an orifice plate is a precision instrument. In best circumstances, the inaccuracy of Orifice plates can possibly fall in the range of 0.75-1.5% AR.

However, there are numerous error causing conditions which can terribly affect the accuracy of an Orifice plate.

Following factors are used to judge the performance of an Orifice plate:

  • Precision in the bore calculations
  • Quality of the installations
  • Condition of the plate itself
  • Orifice area ratio
  • Physical properties of the fluid flow under measurement

Further class of installation depends upon following factors

  • Tap location and circumstance. Generally, there are three ways to position a pressure tap.
  • Provision of the process pipe
  • Competence of straight pipe runs
  • Gasket intervention
  • Misalignment of pipe and orifice bores
  • Lead line design

Extra detrimental conditions consist of

  • Dulling of the sharp edge or nicks caused due to corrosion or erosion.
  • Warpage of the plate because of waterhammer and dirt.
  • Grease or secondary phase deposits on any of the orifice surface.

Any of the above said conditions has the tendency to affect the discharge coefficient of an orifice plate to a large extent

What is a Venturi Tube?

The venturi tube, illustrated in Figure, is the most accurate flow-sensing element when properly calibrated. The venturi tube has a converging conical inlet, a cylindrical throat, and a diverging recovery cone. It has no projections into the fluid, no sharp corners, and no sudden changes in contour.

Venturi Tube

The inlet section decreases the area of the fluid stream, causing the velocity to increase and the pressure to decrease. The low pressure is measured in the center of the cylindrical throat since the pressure will be at its lowest value, and neither the pressure nor the velocity is changing.

The recovery cone allows for the recovery of pressure such that total pressure loss is only 10% to 25%. The high pressure is measured upstream of the entrance cone. The major disadvantages of this type of flow detection are the high initial costs for installation and difficulty in installation and inspection.

Explain about Concentric, Segmental and Eccentric Orifice Plates ?

The concentric orifice plate is the most common of the three types. As shown, the orifice is equidistant (concentric) to the inside diameter of the pipe. Flow through a sharp-edged orifice plate is characterized by a change in velocity. As the fluid passes through the orifice, the fluid converges, and the velocity of the fluid increases to a maximum value.

At this point, the pressure is at a minimum value. As the fluid diverges to fill the entire pipe area, the velocity decreases back to the original value. The pressure increases to about 60% to 80% of the original input value. The pressure loss is irrecoverable; therefore, the output pressure will always be less than the input pressure. The pressures on both sides of the orifice are measured, resulting in a differential pressure which is proportional to the flow rate.

Concentric, Segmental and Eccentric Orifice Plates

Segmental and eccentric orifice plates are functionally identical to the concentric orifice. The circular section of the segmental orifice is concentric with the pipe. The segmental portion of the orifice eliminates damming of foreign materials on the upstream side of the orifice when mounted in a horizontal pipe. Depending on the type of fluid, the segmental section is placed on either the top or bottom of the horizontal pipe to increase the accuracy of the measurement.

Eccentric orifice plates shift the edge of the orifice to the inside of the pipe wall. This design also prevents upstream damming and is used in the same way as the segmental orifice plate.

Orifice plates have two distinct disadvantages; they cause a high permanent pressure drop (outlet pressure will be 60% to 80% of inlet pressure), and they are subject to erosion, which will eventually cause inaccuracies in the measured differential pressure.

What is the selection criteria for Magnetic flowmeters ?

The key questions which need to be answered before selecting a magnetic flowmeter are:

  • Is the fluid conductive or water based?
  • Is the fluid or slurry abrasive?
  • Do you require an integral display or remote display?
  • Do you require an analog output?
  • What is the minimum and maximum flow rate for the flow meter?
  • What is the minimum and maximum process pressure?
  • What is the minimum and maximum process temperature?
  • Is the fluid chemically compatible with the flow meter wetted parts?
  • What is the size of the pipe?
  • Is the pipe always full?

What are the Head type flow meters ?

In these head type flowmeters, some devices is inserted into a pipe carrying fluid. It obstructs the flow of fluid and creates a pressure difference on either side of the device.

The most commonly used devices are as follows:

  1. Orifice plate.
  2. Venture plate.
  3. Flow nozzle.
  4. Doll flow tube.
  5. Pilot tube.

The basic principle of all such devices is that due to obstruction, the velocity of the fluid increases and the pressure decreases. Then the volume flow rate is proportional to the square root of pressure difference across the obstruction. To measure pressure difference, diaphragm based differential pressure transducer is used.

What is a Pitot Tube or Total Pressure Probe?

A probe is a device used for point pressure measurement in a flowing fluid. This point measurement of pressure is done to determine fluid flow rate. The most popular probe is the “PITOT TUBE” which is one of the total pressure probes. The Pitot tube measures the combined pressure (static pressure + impact pressure). The pitot tube has one impact opening and eight static openings as shown in the diagram. The impact opening is provided to sense impact pressure and the static opening are provide to sense static pressure.

The pitot tube is introduced in the fluid flow area where point pressure details is required (which is an indirect measure of flow rate).

The pressure in the outer tube is the static pressure in the line. The total pressure in the inner tube is greater than static pressure. That is, total pressure is the static pressure plus the impact pressure. The differential pressure (P1-P2) is measured using a differential pressure sensor. This differential pressure becomes a measure of flow rate at that point where the pitot tube is present in the flowing fluid.

What is a ‘k’ factor on a turbine meter?

Each turbine meter is specified with a ’k’ factor which represents the number of pulses produced per a known quantity of liquid.

Example: k = 265 pulsed/gallon

Generally, the ‘k’ factor is provided by the manufacturer.

What are the Types of Thermal mass flow meter ?

Thermal mass flow meter types

  1. Constant Current Method
  2. Constant Temperature Method

What is Flow profile or velocity profile ?

The relative velocities of a fluid as it moves through a pipe, the velocity at the center being greater than the velocity at the pipe wall. Laminar flow is characterized by large differences in velocity along the profile, while turbulent flow exhibits a “flatter” profile with more consistent velocity across the pipe diameter. Relevant to insertiontype flowmeters such as Pitot tubes where the flowing velocity is sampled at only one point in the flowstream.

How do you convert NM3/hr to MMSCFD ?

Assume this is a gas. Different industries use different temperatures for “standard,” including but not limited to
15 °C, 60 °F, 20 °C, and 25 °C. Unless you know which “standard” is meant, the final step is not possible.

Nm³ means the gas is measured at 0 °C and 1 atm (101.325 kPa).

Step (1): Multiply by 24 h/day to get Nm³/day.

Step (2): Multiply by 35.31467 ft³/m³ to get cubic feet/day at 0 °C and 1 atm.

Step (3): Determine “standard” temperature in °C, and multiply by temperature correction factor (273.15 + T)/273.15 to get SCFD.

Step (4) divide by 1 million to get MMSCFD.

What are the Types of Flow ?

In general, we come across two types of flow in liquid flow Measurement operations.

Laminar flow: This type of flow occurs at very low velocities or high viscosities. In this, the liquid flows in smooth layers with the highest velocity at the center of the pipe and low velocities at the boundary (wall) of the pipe where the viscous forces hold it back.

Turbulent flow: It takes place at high velocities or low viscosities. In this, the liquid flow breaks up into turbulent eddies which flow through the pipe with the identical average velocity. In this type of flow, fluid velocity is not much significant, and the velocity profile is a lot more uniform in shape.

What are the Factors Affecting Flow Rate ?

From the basic relationship, we deduce that factors affecting liquid flow rate comprises average velocity of the flow and cross sectional area of the pipe. Apart from these, other factors which can influence liquid flow rate are:

  • Liquid’s viscosity
  • Density
  • Friction of the liquid in contact with the pipe

What are the Types of Ultrasonic Flowmeters ?

Ultrasonic flowmeters are two types:

Doppler meters:

Doppler meters measure the frequency shifts caused by liquid flow. In this, two transducers are mounted in a case attached to one side of the pipe. A signal of known frequency is transmitted into the liquid to be measured. Solids, bubbles, or any other discontinuity in the liquid, cause the signal to be reflected to the receiver element. Since the liquid causing the reflection is moving, the frequency of the returned pulse is shifted. This frequency shift is proportional to the liquid’s velocity or flow rate.

A portable Doppler meter which is competent enough of being operated on AC power or from a rechargeable power pack has lately been introduced. A typical Doppler meter using sound pulse reflection principle.

Time-of-travel meters:

These are also known as Transit meters. They have transducers installed on each side of the pipe. They use the transit time principle for flow measurement. In this, opposite sending and receiving transducers are employed to transmit signals through the flow. The signal travels faster when moving with the flow stream rather than against the flow stream. The difference between the two transit times is used to determine the flow rate.

As per configuration, the sound waves travel between the devices at a 45 degree angle to the fluid flow direction. The speed of the signal traveling between the transducers depends upon (increases or decreases) the direction of transmission and the velocity of the liquid being measured. A time-differential relationship proportional to the flow can be acquired by transmitting the signal alternately in both directions.

A major limitation of time-of-travel meters is that the liquids being measured must be moderately free of entrained gas or solids. This is crucial for minimizing signal scattering and absorption.

What are the Types of Variable Area Flowmeters ?

Variable area flowmeters are available in following variety of designs

  1. Rotameter (a float in a tapered tube)
  2. Orifice/Rotameter combination i.e. Bypass Rotameter
  3. Open-channel variable gate,
  4. Tapered plug, and
  5. Vane or Piston designs

What are the Advantages & Disadvantages of Vortex-Shedding Flow Meters ?


  • Accurate regardless of temperature, pressure, density and viscosity when flow is turbulent.
  • Suitable for measuring liquids, gases and steam.
  • Excellent for metering steam flow.


  • Flow must be turbulent.
  • Ineffective for slurries and viscous flow.

How to convert SCFM to ACFM Conversion ?

ACFM = SCFM x 14.696 / (Pa + 14.696) x degrees F / 530

Where as:

ACFM = Actual Cubic Feet per Minute measured gas flow

SCFM = Standard Cubic Feet per Minute gas flow

Pa = Operating Pressure in (PSIA) = PSIG + 14.696

Ta = Temperature in degrees Rankine = F + 460

Note: All calculations are at sea level.

What is Cryogenics and which Flow Meter Works with Cryogenic?

Cryogenics is the study of low temperatures.

The turbine flow meter is a very good choice of measurement due to the material and its ability to hold up to cryogenic temperatures and to accurately repeat at any flow rate.

The turbine creates minimal pressure drop or flow constriction in a catastrophic failure.

Flows can be maintained under any circumstance.

The turbine is also the most accurate and durable for use in a transport due to vibration resistance.

Why Generally a Flow Transmitter Installed Upstream of a Flow Control Valve?

A flow transmitter is always installed on the upstream of the flow control valve in order to maintain the operating pressure across the flow transmitter sensors. Downstream of the control valve the pressure changes as the control valve open or closes.

What is the Purpose of Orifice Vent Hole?

Vent hole is a small hole which is provided in the upper region of orifice plate. Vent hole is required in liquid flow service where gas entrainment may occur.

Vent hole size could affect the accuracy of flow measurement. However, if the diameter of the vent hole is less than 10% of the orifice bore, then the unmeasured flow is less than 1% of the total flow.

Vent hole is not recommended in dirty fluid service or slurries as the hole could be plugged. In this application, the use of eccentric orifice plate becomes alternative.

What is the Purpose of Orifice Drain Hole? 

Drain hole is a small hole which is provided in the lower region of orifice plate. Drain hole is required in gas flow service where liquid entrainment may occur.

Drain hole size could affect the accuracy of flow measurement. However, if the diameter of the drain hole is less than 10% of the orifice bore, then the unmeasured flow is less than 1% of the total flow.

Drain hole is not recommended in dirty fluid service or slurries as the hole could be plugged. In this application, the use of eccentric orifice plate becomes alternative.

Explain about Restrictive Flow Orifice ?

A Restrictive Flow Orifice (RFO) is a type of orifice plate. They are used to limit the potential danger of an uncontrolled flow from, for example, a compressed gas cylinder by:

  1. limiting the accidental release of a hazardous gas (flammable, toxic, etc.) resulting from regulator or other component failure,
  2. restricting flow in a system in order to assure adequate pressure relief valve sizing and system over pressure protection, or
  3. restricting flow from bulk sources

What are the Types of Positive displacement meters ?

The following are the Positive displacement flowmeters

  1. Reciprocating Piston type.
  2. Rotating or Oscillating Piston type.
  3. Nutating Disc type.
  4. Fluted Spiral Rotor type.
  5. Sliding vane type.
  6. Rotating vane type.
  7. Oval Gear type.

Which cable should be used to connect Transmitter?

Generally three-core, twisted and shielded, 19/36 gauge cable. In applications requiring mechanical ruggedness, we recommend three-core 1.5 mm² armored (shielded) cable.

 Can we install the flow meter in vertical/inclined pipeline ?

Yes, the flow meter can be installed in a vertical, inclined or in any angular position of pipeline for compressible fluids like low pressure air/gas, compressed air/gas.

For liquid applications in a vertical pipeline, the direction of flow should necessarily be from bottom to top, so as to avoid flow separation phenomenon.

Why is a ground strap required?

Ground strap is required for proper grounding (Earth) of meter body, i.e. both pipe and meter body should be at the same voltage potential.

Which gaskets are recommended?

For general applications asbestos grade or any non-yielding gaskets are required (Champion #20 or equivalent). NEVER use rubber gaskets!!!

Gasket I.D. must be 5mm larger than the meter I.D. Gaskets must be non-yielding so that they do not protrude and obstruct the flow.

Where should we place the taps for pressure gauges and temperature gauges?

Pressure gauge should be located within a distance of 4D to 7D on either upstream or downstream of the meter body. Pressure tap fittings must not protrude in the pipe. Tap holes must be burr free.

RTD Temperature tap must be placed on the downstream side of the flow meter and within a distance of 5D to 10D from the flow meter body (since a temperature measuring probe /thermo-well can interfere with vortex generation)

 Is the Flow Meter multi-variable?

No, the flow meter measures only the actual flow at operating pressure and temperature conditions i.e. AM³/HR or ACFM.

How do we pack the flow meter to send for servicing if required?

The Flow Meter system should be packed using adequate (2″-3″ thick) thermocol on all 6 sides inside a plywood box to avoid any transit damages.

Flow Meter and Flow Indicator should be packed in separate boxes.

“Used Goods / Goods for Repairs” Declaration should be accompanied with the consignment.

Reference : inconel flow meters

PLC Program for Positive edge pulse output for one scan cycle


This is PLC Program for Positive edge pulse output for one scan cycle.

Problem Description

In some applications, we need to run an operation/function based on external input signal. We can use a digital input as trigger command to activate that required function. Sometimes we use positive transition of the digital input signal to trigger the command instead of continuous/full pulse digital input signal.

Here we consider an example of simple logic in which two registers values will be increment after receiving the trigger command. Each register have a preset value say value “1”. So on every trigger command, the adder register values will be increment by value “1”.

For adder 1 register we use positive edge (0 to 1) triggered input and for adder 2 register we use simple digital input  (0 to 1 & 1 to 0) signal. We see the advantages and disadvantages of using triggering command with and without using positive edge.

We can use the same logic in other applications like Zeroing the register values, forcing the register values with defined value with little logic modification etc.

Problem Diagram

PLC Program for Positive edge pulse output for one scan cycle

Problem Solution

  • We can solve these types of problem by positive edge or rising edge of the digital input. Here we will consider S7-300 PLC for programming, so we can monitor the value and simulate it. We can use PLC SIM for simulation purpose.
  • Here we have considered one simple example. In this example we will consider “Adder 1” register which will add value “1” when transition occurs from 0 to 1 of the trigger command. The register value will be incremented by value 1 after each triggering.
  • For “Adder 2” register, the value will be incremented after receiving the digital input. Here, we are not used the positive edge triggering.


Here is PLC program for Positive edge pulse output for one scan cycle.

List of Inputs/Outputs

Inputs List:-

Outputs List:-

Memory Coil:-

  • Positive Edge of trigger command : M0.0
  • Total Value = MW2
  • Total Value 2 = MW4

Ladder diagram for Positive edge pulse output for one scan cycle

Network 1 : The initial value of “Adder 1″register is zero. After giving positive edge triggering command for 18 times, the output will be value 18 as it increments by value “1”.

Ladder diagram for Positive edge pulse output - 1

Simulation (PLCSIM-300) for trigger command with positive edge.

Network 2 : The initial value of “Adder 2″register is zero. After giving triggering command (without positive/negative edge) for 18 times, the output will come some random number (say 7506) instead of value 18 as trigger command directly received.

Ladder diagram for Positive edge pulse output - 1

Simulation (PLCSIM-300) for trigger command without positive edge.

Program Description

  • In this application, we have used Siemens S7-300 PLC and TIA Portal Software for programming.
  • Here we have considered two examples for positive edge explanation. Anyone can easily understand the concept.
  • In Network 1, when trigger command (I0.0) is triggered then transition will occur from 0 to 1 and positive pulse instruction will be executed.
  • Say “Adder 1″register will be stored with value “1” in MW0, if trigger command (I0.0) will be triggered then the value will be incremented by “1”.
  • Here for example, we have triggered 18 times when adder 1 is zero, so adder added 18 in total Value (MW0)
  • Another example we have taken in Network 2,  without using positive pulse. so here you can see the result.
  • Say, We have pressed or triggered 18 times but it added 7506 (this is random value it can be different during simulation) in total Value 2 (MW4) so it is not proper addition. Because one pulse have rising or falling edges / positive or negative pulses (o to 1 and 1 to 0).
  • Here also we have used PLC SIM for simulation, so we can simulate the total addition. In first network we have added positive edge so simulator is showing 18. In second network we have added trigger command without positive edge so it is showing some random value.
  • This is the concept of positive edge, we can use this positive edge during any programming application.
  • Above program and simulation is only for explanation purpose and simulation value can be different at simulation time.

Runtime Test Cases

Positive edge pulse output for one scan cycle

Note : The above PLC Logic provided for basic idea about application of Positive edge trigger command in PLC Logic. The Logic is limited and not complete application.

Article by
Bhavesh Diyodara

PLC Program for Automatic Bottle Rejection System


This is PLC Program for Automatic Bottle Rejection System.

Problem Description

Now a Days the Automation in industries is necessary for Accurate & Fast Production.

Let’s Take an Example of soda bottle companies, where the belt conveyor is used for transferring the bottles from one station to another station.

But before bottles reach at soda filling station it is necessary to make all bottle are in standing position for further processing

Fallen bottle on the conveyor may create problem in next process. so here we discuss a simple PLC Logic which handles the fallen bottle.

Problem Diagram

PLC Program for Automatic Bottle Rejection System

Problem Solution

  • So for that we use PLC system at filling station, which reject the fallen bottle from the conveyor & clear the path for the next process.
  • This process is made by using sensors & actuators. We use pneumatic piston cylinder assembly for pushing the fallen bottles from the conveyor.
  • When conveyor is running, then all bottles transfer form one station to other station for next process. There are two sensors are used, for standing and fallen bottles detection, one pneumatic cylinder for pushing the fallen bottle from the conveyor.


Here is PLC program for Automatic Bottle Rejection System.

List of Inputs/Outputs

Inputs List:-

  • Start PB-I0.1
  • Stop PB-I0.0
  • Sensor X1-I0.2
  • Sensor X2-I0.3

Outputs List:-

  • Cycle ON -Q0.0
  • Conveyor-Q0.1
  • Cylinder -Q0.2

Ladder diagram for Automatic Bottle Rejection System

PLC Ladder Logic for Automatic Bottle Rejection System

Program Description

  • In this application, we have used Siemens S7-1200 PLC and TIA Portal Software for programming. We can also design this logic with relay circuit also.
  • In Network 1, we have taken cycle ON condition for machine. Here we have taken START PB (I0.1) for starting the cycle and STOP PB (I0.1) for cycle STOP.
  • We have taken parallel output of conveyor (Q.1) with cycle ON (Q0.0) so we can operate conveyor with cycle ON condition.
  • In Network 2, we have taken sensors X1(I0.2) and X2(I0.3) as inputs. We used NO contact for X2 (I0.3) sensor and NC contact for X1 (I0.2) sensor.
  • When Bottles are transferring on the conveyor, these sensors sense the position of the bottles whether they are standing or fallen.
  • Sensor X2(I0.3) sense down position of the Bottle & Sensor X1(I0.2) Sense top position of the bottle.
  • In PLC, we designed the circuit which follows command that if sensor X2(I0.3) sense the bottle & sensor X1(I0.2) does not sense the bottle then
    the pneumatic actuator (Q0.2) will come in action & it will reject the bottle from the conveyor.
  • After this, the perfect bottles will go in the soda filling station & whole cycle will be completed.

Runtime Test Cases

PLC Program for Automatic Bottle Rejection System Test Cases


Note : The above PLC Logic provided for basic idea about application of PLC in Automatic Bottle Rejection Handling System. The Logic is limited and not complete application.

Article by
Bhavesh Diyodara

PLC Program for Daily Production Record


This is PLC Program for Daily Production Record.

Problem Description

In many industries, It is required to count the numbers of products which are made in one day and it is very necessary for selling the products or track the production quantity on daily basis.

In olden days, human operator is allotted for counting the final products but because of some human errors, precise counting is not possible. Therefore we cannot get proper counting of all products and unable to track the production quantity effectively.

Mostly these types of problems occur in food and beverage industries, box packaging industries, bottle filling application etc. So we can use a simple PLC based logic to track the daily production and to record it electronically.

Problem Diagram

PLC Program for Daily Production Record

Problem Solution

  • Here we will solve the problem of counting of final products by using sensors and PLC programming. First sensor sense the product and counts the quantity and the value will be shown on the digital display (as shown in above figure).
  • For easy explanation, we will consider one simple example of empty box counting system. In this system empty boxes are travelling form first process to second process (say one place to another).
  • Sensor is used for counting the empty boxes. So when sensor will detect empty box then display will start , say starts count from  1 and this is done by simple logic.
  • Every 24 hours  / after one day, we can reset the counter value by using RESET button. Here we will consider two batches of production for easy explanation.
  • And also we have considered two batches completion indications for operator for each batch which will display on the Local Panel. By PLC logic we will implement the desired logic.
  • So when any batch will be completed then indication lamp will be ON as per PLC program.
  • Once production target will be completed, display counter can be reset by using RESET button.


Here is PLC program for Daily Production Record.

List of Inputs/Outputs

Inputs List:-

  • Box detector Sensor=I0.0
  • Reset= I0.1
  • Main SWITCH=I0.2

Outputs List:-

  • Target completed: – Q0.0
  • Batch 1 completed: – Q0.1
  • Batch 2 completed:- Q0.2

Ladder diagram for Daily Production Record

PLC Ladder Logic for Daily Production Record

Program Description

  • In this application we have used Siemens S7-1200 PLC and TIA Portal Software for programming.
  • In Network 1 we used Main SWITCH (I0.2) to start the system/batch and we used NO contact of box detector sensor (I0.0) in series. Here we considered one UP counter so when box detector sensor (I0.0) detects  the box then counter will starts counting.
  • Here also we have taken target completed output (Q0.0) for target completion indication for the operator indication on the panel. By pressing RESET button (I0.1) operator can RESET the old production record.
  • Counter operation is used to count the products, in which RESET (I0.1) used for reset the production record. And Preset value (PV) is 20 products. Counter value (CV) is MW2 indicates the actual number of products detected by sensor & this value will be used in the following rungs to track the batch status.
  • In Network 2 we used batch1 logic from counter block output CV. Here we used comparator for counting 10 boxes for batch 1 and when it will be completed then batch 1 completed lamp (Q0.1) will ON. In this add equal to equal comparator in which input is (MW2) and for 10 products.
  • In network 3 we used batch 1 logic from counter block output CV. Here we used comparator for counting 20 boxes for batch 2 and when it will be completed then batch 2 competed lamp (Q0.2) will ON
  • And this way we can decide that how many products and batches are produced.

Runtime Test Cases

PLC Program for Daily Production Record RunTime Test Cases

Note : The above PLC Logic provided for basic idea about application of PLC in industrial production record. The Logic is limited and not complete application.

Article by
Bhavesh Diyodara

Barkhausen Criterion


Barkhausen Criterion :

Consider a Inverting Amplifier with Open Loop Gain, A.

The feedback network attenuation factor is β which value is less than unity.

A basic inverting amplifier produces 1800 phase shift between input and output, which is shown in below figure.

Inverting Amplifier

An input voltage Vi is applied to the amplifier and the output Vo value depends on the feedback network.

The basic inverting amplifier output will be 1800 phase shift with its input. We need a feedback network which provide a signal such that it must be in-phase with the input of the amplifier. So here we need Positive Feedback network which provides 1800 phase shift. The output of Amplifier is connected as input to the feedback network and the feedback network provides 1800 phase shift. The output of feedback network will be in-phase with the amplifier input as shown in below figure.

Diagram of Oscillator Circuit

Consider an input voltage Vi is applied to the amplifier and the output voltage will be

Vo = A Vi

The feedback network attenuation factor, β decides the output value of feedback network

Vf = β Vo

By substituting the above two equations, we have

Vf = β A Vi

For the Oscillator, there will be no additional input signal i.e. the feedback signal Vf must act as input to the amplifier. so we have

| A β |  = 1

As discussed above, the feedback network will produce 1800 phase shift inaddition to the inverting amplifier such that total phase shift of the loop/circuit will be 3600 phase shift.

In this case, the feedback voltage Vf will be sufficient to generate the output oscillations without any external input.

The two conditions discussed are required for a circuit to work as an oscillator are called as Barkhausen Criterion

  1. The Total Phase shift of the loop or circuit must be 3600 phase shift. The amplifier provides 1800 phase shift and the feedback network provides another 1800 phase shift. so the total phase shift of the circuit is 3600 phase shift.
  2. The Product of magnitude of amplifier open loop gain (A) and the magnitude of feedback network factor (β) must be unity. | A β |  = 1

If a circuit satisfies the above two conditions then it will generate constant oscillations with defined frequency & magnitude without using any external input.