Lab Experiment for Process Control Simulator

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EXPERIMENTAL SECTION

Experiment – 1

AIM

To determine the time constant and transfer function of first order process.

PROCEDURE

☞Connections are made as per the connection diagram shown in figure.

☞Keep the set value pot to zero.

☞Give the square wave (step input) of around 30 Hz and amplitude of one VP-P to the process input points as shown in figure.

☞Observe the input and output waveforms on the CRO / Storage Oscilloscope

☞This time is set to be the time constant of the process and calculate Lag and Gain of the process from the output response.

MODEL GRAPH

EXPERIMENT – 2

AIM

To observe the time response of closed loop second order process with proportional control.

SUMMARY

The system considered in experiment- had one major disadvantage, namely that there is considerable deviation present at all times. As deviation should operate the system, this implies that sensitivity is too low. In Process control this sensitivity is defined in terms of the proportional band.

This is the range of values of deviation that causes the controller output to cover its full operating range. This is often expressed as a percentage such that 100% proportional band means that the full range of outputs of the measuring systems causes the controller to operate over its full range.

An adjustment of the percentage of the proportional band varies the gain of the controller. The following experiment will examine the effects of changes in percentage of the proportional band and the response of the system to disturbances.

PROCEDURE

☞Connections are made as per the connection diagram shown in figure.

☞Keep the set value pot to zero.

☞Apply a square wave signal of 2VPP at around 30 Hz.

☞Alternatively display in the oscilloscope the set value disturbance point and measured value from the point PV.

☞Repeat all the above steps with the percentage proportional band 50% and 40%.

☞Observe the response and find the peak overshoot (Mp), Rise time (tr), Peak time (tp), Damping ratio (?) and settling time (ts) and also tabulate the readings.

MODEL GRAPH

TABULATION

%PBPeak Overshoot MpRise Time tr Rise Time tpDampingRatioSettingtime ts
      

Kp= 100% / PB%

RESULT

Thus the time response of closed loop second order process with proportional control was studied.

EXPERIMENT – 3

AIM

To study the time response of P + I controller.

SUMMARY

The proportional control to maintain a stable system the gain level is such that the system is insensitive to deviation below the certain level. In an ideal system the measured value and the set value should be the same under steady state condition the deviation should be zero.

What is required is an alternative signal to be fed into the main amplifier of sufficient size to provide an output if a steady state deviation exists viz to reduce the offset to zero. Such a signal can be provided by an integrator which gives a constantly increasing output for a steady value input. Such an arrangement is known as proportional + Integral Controller and should reduce any steady state deviation to zero.

PROCEDURE

☞Connections are made as per the connection diagram shown in figure.

☞Keep the set value pot at zero.

☞Apply a square wave of 2VP-P at around 30 Hz.

☞Adjust the proportional band control until the system settles with 2 to 3 overshoots.

☞Now connect the integral section as shown in figure

☞Slowly reduce the integral action time until the deviation falls to zero.

☞Observe the response and calculate the Proportional Band (PB), Integral time, peak overshoot (Mp), Rise Time (Tr) and settling time (Ts) and tabulate the readings.

Model Graph

Tabulation

S.NOProportiaonaI Band PBIntagral Time Peak OvershootMpRiceTimeTrSettingtime ts
      

RESULT

Thus the time response of P + I controller was studied.




EXPERIMENT – 4

Aim

To study the response of P + I + D Controller in a process.

Summary

As seen in experiment the integral control improves the performance of the control system in some respects, i.e it reduces the steady state deviation, but has the disadvantage of slowing down the overall response time.

If a System is required to follow a sudden change in set value this would give rise to a rapid change in the deviation. Although this deviation change is rapid the system response rather slowly, So if at this time the controller output can be boosted, the speed of system response will be improved.

If the deviation is differentiated, i.e rate of change measured, and a signal produced proportional to this and then added to the signals from the proportional and integrator sections, some improvement may result. Such an arrangement is known as three term controller or PID controller

PROCEDURE

☞Connections are made as per the connection diagram shown in figure.

☞Apply a square wave of 2VP-P at around 50Hz.

☞Now patch E2,I3 and I1,I2and adjust the integral time until the steady state deviation is zero

☞Now note down the number of overshoots before the system settles.

☞Now connect E3, D3 and D1, D2 and slowly increase the derivative time and note down the effect of this system response.

☞Observe the response and calculate the Proportional Band (PB), Integral time (Ti), Rise Time (Tr), Settling time (Ts) and Peak Overshoot (Mp) and also tabulate the readings

Tabulation

ProportionalBand (PB)IntegralTime (Ti)Rise Time(Tr) peak Time(Tp)Settingtime (Ts)PeakOvershoot(Mp)
      

MODEL GRAPH




RESULT

Thus the response of P + I + D Controller in a process was studied.



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