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What is an Oscillator ?

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What is an Oscillator ?

An oscillator is an amplifier that acts as a generator by using positive feedback concept.

Oscillator does not require any input signal. It produces an output waveform of constant amplitude and constant frequency up to several hertz as required (Depends on Resistor & Capacitor Values). It produces output oscillations as long as it is connected to DC power source.

How an Oscillator starts oscillating ?

Every resistors used in the circuit has some free electrons in it that moves randomly around in various directions. Due to their movement electrons generates a voltage called noise voltage. Noise voltage contains all sinusoidal frequencies. The noise voltage has a low amplitude and it is amplified which appears across output. This amplified noise drives the feedback network. At a particular frequency, the feedback voltage is maximum, which is represented as Frequency of Oscillation.

What is Feedback ?

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Concept of Feedback:

It is used most commonly in an amplifier. Part of the output from the amplifier is fed back to the input and this concept is called feedback.

When the input signal of amplifier and part of the output are In-phase with each other, it is called as Positive feedback.

When the input signal of amplifier and part of the output are Out-phase with each other, it is called as Negative feedback.

The concept of positive feedback results in oscillations, so they are used to generate oscillations of particular frequency as required. Such circuits are called as Oscillators.

Positive Feedback Principle

PLC Program for Water filling and Discharging Process

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This is PLC Program for Water filling and discharging process using S7-1200 PLC.

Problem Description:-

  • In many industries or plant, there are lots of manual water filling system are used for water storage.
  • In manual system, there are so many disadvantages such as Accuracy, time delay problem, loss of liquids, Time consuming.
  • And due to manual system we have to arrange an operator for machine operation. Water wastage occurs due to manual system
  • Here we are discussing a semi-automatic system.

Problem Diagram

PLC Program for Water filling and Discharging Process

Problem Solution

  • To solve this problem, we will use S7-1200 PLC for programming.
  • Here we use two sensors for level measurement, one is for High level and second is for low level.
  • We use feeding valve (MV1) for filling Cycle of the tank and discharge valve  (MV2) for discharging cycle of the tank. Both will be controlled according to sensor logic. So when the water level goes below low level then feeding valve will turned ON automatically and when water level reaches high and the it senses by high level sensor, then discharging process will be turned ON automatically.
  • When high level is detected then buzzer will turn ON for alarm purpose. Cycle will stop if user will press stop button from the control panel.

Program

Here is PLC program for Water filling and discharging process using S7-1200 PLC.

List of inputs/outputs

Digital Inputs

  • Start PB = I0.0
  • Stop PB = I0.1
  • TLB 1 = I0.3
  • TLB 2 = I0.2

Digital Outputs

  • Cycle ON = Q0.0
  • Valve MV1 (Feed) = Q0.1
  • Valve MV2 (Discharge) = Q0.2
  • Agitator/Mixer M  = Q0.3
  • Buzzer = Q0.4

Ladder diagram for Water filling and discharging process using S7-1200 PLC

PLC Program for Water filling and Discharging Process

Program Description

  • For this application, we used S7-1200 PLC and TIA portal software for programming.
  • In Network 1 we used latching circuit for cycle ON (Q0.0) output. It can be started by pressing START PB (I0.0) and stop by pressing STOP PB (I0.1).
  • When cycle will be started then system will check level of the tank. If tank level is low then then feeding process will start and tank level is high then Discharge cycle will start.
  • Here we have taken NO contact for both sensors in the program for simplicity. It can be done by relay logic in field or you can use such type of sensors.
  • When tank will detect low level then TLB 2 (I0.2) will be activated and then feeding cycle will be ON. Here we have taken NC contact of TLB1 (I0.3) so when PLC will detect high level then it will stop Feeding cycle.
  • When tank will detect high level then TLB 1 (I0.3) will be activated and discharging cycle will be ON. Here we have taken NC contact of TLB2 (I0.2) so when PLC will detect low level then it will stop discharge cycle cycle.
  • Mixer M (Q0.3) should be ON during discharging cycle for mixing purpose.
  • Here we also considered an alarm for high level to inform operator. When TLB 1(I0.3) will be detected then buzzer (Q0.4) will be activated.
  • During all function, cycle should be ON.

Runtime Test Cases

PLC Program for Water filling and Discharging Simulation

Article by
Bhavesh Diyodara

PLC Program for Automatic Liquid Mixing Application

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This is PLC Program for Automatic Liquid mixing Application.

Problem Description:-

  • In many industries, there are lots of mixing system are used for solutions mixing. Some plants use complete automation or semi-automation.
  • In manual system, there are so many disadvantages such as lack of Accuracy, Time delay problem, loss of liquids, Time consuming etc.
  • Here we are discussing semi-automatic application of mixing system.

Problem Diagram

Automatic Liquid Mixing Application

Problem Solution

  • For this example, we use PLC programming and for that we use Siemens S7-1200 PLC.
  • For easy explanation, we can consider simple example of mixing system as shown above.
  • In this application pure unmixed solution can be prepared by the operator using switches S1 and S2. And mixed solution or material can be prepared by the operator using switch S3.
  • Operator observes the level of the tank and he can discharge the liquid inside tank by operating valve V5. Also the agitator motor M will be  in running while tank is being filled. We will provide interlock system so operator cannot operate both switches at same time.
  • V1, V3 and V5 are manual valves which is not connected to the PLC.
  • V2 and V4 are electronically operated valves which can be controlled by PLC.

Program

Here is PLC program for Automatic Liquid mixing Application.

List of inputs/outputs

Digital Inputs

There are three switches S1, S2 & S3

  • S1 = I0.0
  • S2 = I0.1
  • S3 = I0.3

Digital Outputs

We have two valves V2 & V4. one Agitator Motor M1

  • V2 = Q0.0
  • V4 = Q0.1
  • M1 = Q0.2

Ladder diagram for the Automatic Liquid mixing Application

PLC Program for Automatic Liquid Mixing Application

Program Description

  • For this application, we used S7-1200 PLC and TIA portal software for programming.
  • In Network 1, we have taken NO contact of S1 (I0.0) and NC contact of S2 (I0.1) and S3 (I0.2) in series. By activating switch S1 operator can START the valve V2 for solution 1 (Liquid 1 ).
  • In Network 2, we have taken NO contact of S2 (I0.1) and NC contact of S1 (I0.0) and S3 (I0.2) in series. By activating switch S2 (I0.1) operator can START the valve V4 (Q0.1) for solution 2 (Liquid 2 ).
  • For both Networks 1 & 2,  A parallel connection we have taken, NO contact of S3 (I0.2) and in series with  NC contact of S1 (I0.0) and S2 (I0.1).
  • Because of the above parallel connection, operator can operate both valves by activating switch S3 (I0.2) for mixed solution (Liquid1 & Liquid 2)
  • As per our condition, agitator M1 (Q0.2) should be activated automatically while tank is being filled. So we have taken NO contact of V2 (Q0.1) and in parallel NO contact of V4 (Q0.1) so agitator will be activated automatically by operating any switch.

Runtime Test Cases

PLC Program for Automatic Liquid Mixing Simulation

Article by
Bhavesh Diyodara

PLC Program for Sequential Motor Control

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This is PLC Program for Sequential Motor Operating System.

Problem Description

  • In many industries, there are lots of motors are used. Sometimes we need to start more than one motor in an application. When we have low incoming power supply rating, then there is a chance the incoming MCB will trip when one or more motors will START in parallel because they will consume more power.
  • Here we will consider one similar example where we START each motor one by one.

Problem Diagram

PLC Program for Sequential Motor Control

Problem Solution

  • The problem can be solved by using PLC programming or relay logic.
  • In this case, we have to operate motors sequentially. There are total 3 motors to be controlled in a sequence. so that each motor will start sequentially, say Motor 1 will START then after some delay then motor 2 will start and after some delay motor 3 will start.
  • So that whole operation will take 10 seconds to start all motors in a sequence. By providing this delay we can avoid the problem of taking large
    current by motors during initial stat up.
  • All motors will be operate in the sequence and 5 seconds time delay is to be provided between operations of each motor.
  • Here will write logic for sequential operation for motors using PLC.

Program

Here is PLC program for Sequential Motor Operating System.

List of Inputs/Output

Inputs List:-

  • Start PB =I0.0
  • Stop PB= I0.1

Outputs List:-

  • Cycle on=Q0.0
  • Motor 1=Q0.1
  • Motor 2=Q0.2
  • Motor 3=Q0.3

Ladder diagram for Sequential Motor Operating System

PLC Ladder Logic for Sequential Motor Control

Program Description

  • In this application, we used Siemens S7-1200 PLC and TIA Portal Software for programming. We can also design this logic with relay circuit.
  • In Network 1, we wrote logic for cycle ON condition. Here cycle ON (Q0.0) lamp will indicate cycle status. Cycle can be started by pressing START PB (I0.0) push button and can be Stopped by pressing STOP PB (I0.1) push button.
  • When cycle will be ON, at same time Motor 1(Q0.1) will be Started. And at the same time, timer instruction will be executed.
  • In Network 2, the NO contact of Motor 1  starts Timer T1  and when Timer for Motor 2 (Q0.1) will reach the set value 5 seconds. Then NO contact of the T1 will START the Motor 2 (Q0.1).
  • In Network 3. we have taken logic for motor 3.Here we have given NO contact of motor 2 for starting the timer of motor 3. When T2 will reach the set value 5s ,the NO contact of the T2 will START the Motor 3(Q0.0).
  • When STOP PB (I0.1) will be pressed then NC contact will be activated which makes Cycle (Q0.0) OFF. And also motor 2 and 3 will stop working.

Runtime Test Cases

PLC Program for Sequential Motor Control Simulation

Article by
Bhavesh Diyodara

PLC Program for Automatic Lamp Control in Storage Facility

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This is PLC Program for Automatic lamp Control in Godown (Storage Facility).

Problem Description:-

  • In old process, when the person enters in the godown (Storage facility) , he/she presses the switch and all lamps in the godown will be ON. If we turn on all lamps together then more energy consumption occurs.
  • This problem occur in old process, so solutions is required for this process. We can solve this problem using simple automation or interlock system.

Problem Diagram

Automatic Lamp Control in Storage Facility

Problem Solution

  • We can solve this problem by simple interlock using PLC. As shown in figure, consider one godown for industry and there are couple of segments in the facility.
  • For example, we have considered only three segments for the storage facility. Say here we have 3 lamps for 3 segments and 3 switches for operation.
  • When Person enters the godown (storage facility) for some work, he will operate lamp 1 by pressing switch 1. when work will be completed then operator will turn OFF the light.
  • Here we will provide interlocking system so person cannot operate other segment’s lamp until he stops the first segment lamp. Same case occurs in  other segments.
  • So by using this automation/interlock circuit, we can save energy.
  • Note : This type of interlock applies only to some type of storage facilities as these operated by working in one segment at a time only before going to next segment in the storage facility.

Program

Here is PLC program for Automatic lamp ON/OFF in GODOWN.

List of inputs/outputs

Digital Inputs

  • SW1 = I0.0
  • SW2 = I0.2
  • SW3 = I0.3

Digital Outputs

  • Lamp 1 = Q0.0
  • Lamp 2 = Q0.1
  • Lamp 3 = Q0.2

Ladder diagram for Automatic lamp ON/OFF in GODOWN.

PLC Program for Automatic Lamp Control in Storage Facility

Program Description

  • For this application, we used S7-1200 PLC and TIA portal software for programming.
  • In above program, we have taken NO contact of SW 1(I0.0) for operating the Lamp 1 (Q0.0) and given NC contacts in series. so when user press other switches, Lamp 1(Q0.0) will be OFF.
  • In network 2, we have written logic for Lamp 2(Q0.1). By operating SW2 (I0.2) operator can operate Lamp 2(Q0.1). And given NC contacts in series, so when user press other switches, Lamp 2(Q0.1) will be OFF.
  • In network 3, we have written logic for Lamp 3(Q0.2).By operating SW3 (I0.2) operate can operate Lamp 3(Q0.2). And given NC contacts in series, so when user press other switches, Lamp 3(Q0.2) will be OFF.

Runtime Test Cases

PLC Program for Automatic Lamp Control

Article by
Bhavesh Diyodara

PLC Program for Two Way Switch Logic

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This is PLC Program for Two ways switch logic for staircase light in house

Problem Description:-

  • In duplex type house there are ground floor and first floor and sometimes second floor also.
  • Sometimes people need to go from ground floor to first floor or from first floor to ground floor by staircase provided in house.
  • But in staircase there is no sunlight so people need a lamp/light to see the steps of the staircase easily.
  • Here we are using a simple PLC to control this lamp using two switches, one switch at ground floor and second switch at first floor to control one lamp as shown in below figure.
  • Note : we can also build the circuit using simple relays also. This article only for understanding the basic concept of 2 way switch using  a PLC Ladder Logic.

Problem Diagram

PLC Program for Two ways switch logic for staircase light

Problem Solution

  • We will solve this problem by simple automation. As shown in figure consider one simple house with one floor and staircase is provided in the house.
  • Here we will set lighting system for the users to switch ON/OFF the light whether they are on bottom of the stair or at top.
  • We will provide separate switch for each floor as shown in above figure.

Program

Here is PLC program for two ways switch logic for staircase light in house.

List of inputs/outputs

Digital Inputs 

Digital Outputs

Ladder diagram for two ways switch logic for staircase light in house.

PLC Ladder Logic for Two Way Switch

Program Description

  • For this application, we used S7-1200 PLC and TIA portal software for programming.
  • In above program, we have added two NO contacts of SW 1 (I0.1) and SW 2 (I0.2) in series and NC contacts of SW1 (I0.1) and SW2 (I0.2) in parallel of this series SW1 & SW2 NO Contacts.
  • If the status of the bottom switch (SW1) and status of the top switch (SW2) are same then lamp will be ON. And if either status of the bottom or top switch is different from other then lamp (Q0.0) will be OFF.
  • When lamp (Q0.0) is OFF then user can ON the lamp by changing status of any switch. Also user can turn OFF the lamp by changing the status of one of the two switches.

Runtime Test Cases

PLC Program for Two Way Switch Logic Simulation

Article by
Bhavesh Diyodara

Ionization chamber Principle

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The ionization chamber is the simplest of all gas-filled radiation detectors, and is widely used for the detection and measurement of certain types of ionizing radiation; X-rays, gamma rays and beta particles. Conventionally, the term “ionization chamber” is used exclusively to describe those detectors which collect all the charges created by direct ionization within the gas through the application of an electric field. It only uses the discrete charges created by each interaction between the incident radiation and the gas, and does not involve the gas multiplication mechanisms used by other radiation instruments, such as the Geiger-Müller counter or the proportional counter.

Ion chambers have a good uniform response to radiation over a wide range of energies and are the preferred means of measuring high levels of gamma radiation. They are widely used in the nuclear power industry, research labs, radiography, radiobiology, and environmental monitoring.

Principle of operation

An ionization chamber measures the charge from the number of ion pairs created within a gas caused by incident radiation. It consists of a gas-filled chamber with two electrodes; known as anode and cathode. The electrodes may be in the form of parallel plates (Parallel Plate Ionization Chambers: PPIC), or a cylinder arrangement with a coaxially located internal anode wire.

Ionization chamber Working

Figure : Schematic diagram of parallel plate ion chamber, showing drift of ions. Electrons typically drift 1000 times faster than positive ions due to their much smaller mass.

A voltage potential is applied between the electrodes to create an electric field in the fill gas. When gas between the electrodes is ionized by incident ionizing radiation, ion-pairs are created and the resultant positive ions and dissociated electrons move to the electrodes of the opposite polarity under the influence of the electric field. This generates an ionization current which is measured by an electrometer circuit. The electrometer must be capable of measuring the very small output current which is in the region of femtoamperes to picoamperes, depending on the chamber design, radiation dose and applied voltage.

Each ion pair created deposits or removes a small electric charge to or from an electrode, such that the accumulated charge is proportional to the number of ion pairs created, and hence the radiation dose. This continual generation of charge produces an ionization current, which is a measure of the total ionizing dose entering the chamber. However, the chamber cannot discriminate between radiation types (beta or gamma) and cannot produce an energy spectrum of radiation.

The electric field also enables the device to work continuously by mopping up electrons, which prevents the fill gas from becoming saturated, where no more ions could be collected, and by preventing the recombination of ion pairs, which would diminish the ion current. This mode of operation is referred to as “current” mode, meaning that the output signal is a continuous current, and not a pulse output as in the cases of the Geiger-Müller tube or the proportional counter.

Referring to the accompanying ion pair collection graph, it can be seen that in the “ion chamber” operating region the collection of ion pairs is effectively constant over a range of applied voltage, as due to its relatively low electric field strength the ion chamber does not have any “multiplication effect”. This is in distinction to the Geiger-Müller tube or the proportional counter whereby secondary electrons, and ultimately multiple avalanches, greatly amplify the original ion-current charge.

Ionization chamber Principle

Figure : Plot of ion current against voltage for a wire cylinder gaseous radiation detector. The ion chamber uses the lowest usable detection region.

Scintillation Counter Principle

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A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillator material, and detecting the resultant light pulses.

It consists of a scintillator which generates photons in response to incident radiation, a sensitive photo multiplier tube (PMT) which converts the light to an electrical signal and electronics to process this signal.

Scintillation Counter Theory

Scintillation counters are widely used in radiation protection, assay of radioactive materials and physics research because they can be made inexpensively yet with good quantum efficiency, and can measure both the intensity and the energy of incident radiation.

Operation

When an ionizing particle passes into the scintillator material, atoms are ionized along a track. For charged particles the track is the path of the particle itself. For gamma rays (uncharged), their energy is converted to an energetic electron via either the photoelectric effect, Compton scattering or pair production. The chemistry of atomic de-excitation in the scintillator produces a multitude of low-energy photons, typically near the blue end of the visible spectrum. The number of such photons is in proportion to the amount of energy deposited by the ionizing particle.

Some portion of these low-energy photons arrive at the photocathode of an attached photo multiplier tube. The photocathode emits at most one electron for each arriving photon by the photoelectric effect. This group of primary electrons is electrostatically accelerated and focused by an electrical potential so that they strike the first dynode of the tube. The impact of a single electron on the dynode releases a number of secondary electrons which are in turn accelerated to strike the second dynode.

Scintillation Counter Principle

Each subsequent dynode impact releases further electrons, and so there is a current amplifying effect at each dynode stage. Each stage is at a higher potential than the previous to provide the accelerating field. The resultant output signal at the anode is in the form of a measurable pulse for each group of photons that arrived at the photocathode, and is passed to the processing electronics. The pulse carries information about the energy of the original incident radiation on the scintillator. The number of such pulses per unit time gives information about the intensity of the radiation. In some applications individual pulses are not counted, but rather only the average current at the anode is used as a measure of radiation intensity.

Scintillation Counter Animation

Scintillation Detector Animation

The scintillator must be shielded from all ambient light so that external photons do not swamp the ionization events caused by incident radiation. To achieve this a thin opaque foil, such as aluminized mylar, is often used, though it must have a low enough mass to minimize undue attenuation of the incident radiation being measured.

Detection materials

 The scintillator consists of a transparent crystal, usually a phosphor, plastic (usually containing anthracene) or organic liquid (see liquid scintillation counting) that fluoresces when struck by ionizing radiation.

Cesium iodide (CsI) in crystalline form is used as the scintillator for the detection of protons and alpha particles. Sodium iodide (NaI) containing a small amount of thallium is used as a scintillator for the detection of gamma waves and zinc sulfide (ZnS) is widely used as a detector of alpha particles. Zinc sulfide is the material Rutherford used to perform his scattering experiment. Lithium iodide (LiI) is used in neutron detectors.

Applications

cintillation counters are used to measure radiation in a variety of applications including hand held radiation survey meters, personnel and environmental monitoring for radioactive contamination, medical imaging, radiometric assay, nuclear security and nuclear plant safety.

Reference : Wikipedia

Classification of Control Valves

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Classification of Control Valves

The control valves are basically classified into two types.

  1. Linear and
  2. Rotary.

The below figure shows in detailed classification of control valves based on Linear & Rotary movement.

Control Valves Classification

In addition to LINEAR and ROTARY, control valves are also classified according to their GUIDING METHODS, CHARACTERIZATION METHODS, and the nature of SERVICES they are applied within.

Control Valve Types

The below figure shows simplified version of control valve classification.

Different Types of Control Valves

Reference : cashco