Control System

Control System Questions and Answers

Q. What is the tuning of controllers?

Tuning basically involves proportional adjustment. Integral and derivative parameters to get better control. The gain, time constant and dead times around the loop will determine the settings of various parameters of the controller.

Q. What is the proportional control only?

Proportional control attempts to return the measurement to the set point after the load is upset. It is however impossible for a standard controller to return measurements to a fixed point.

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Q. What is the use of proportional control only?

It is commonly used for level control. It reduces the effect of load change but cannot eliminate it.

Q. What is proportional plus reset control?

A reset action is initiated to remove the offset. It will integrate the difference between the measurement and the set point and change the output of the controller until the difference between the measurement and the set point is zero. The reset will work as long as the error exists.

Q. What is the use of Proportional Plus reset control?

Proportional + reset controllers are common types used in industrial process control and where dead time is high.

Q. What is proportional plus reset plus derivative?

Derivative or rate action helps the controller overcome system inertia and results in faster, more accurate control. A derivative action occurs when the measurement signal changes. Rate action does not work in study conditions. Allows the derivative controller to inject more corrective actions.

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Q. What is the use of proportional plus reset plus derivative?

on temperature controls.

Q. What is Difference Distance Control?

Differential gap control is similar to on-off control except that there is a band or gap around the control point.

Q. What is the use of differential distance control?

In industry, differential gap control is often found in non-critical level control applications where it is desirable to simply prevent the tank from flooding or running dry. When the measured variable is greater than the upper gap, the control valve will either fully open or fully close. Likewise, when it crosses a short distance, it will open or close completely.

Q. Where is closed control used?

On-off control is used when precise control is not required, processes with sufficient capacity to allow the end operator to continue the measurement cycle. And it is mainly used in refrigeration and conditioning systems.

Q. What is reset-wind up?

When a reset action is applied in controllers where the measurement is far from the set point for a long time, the residual output may increase to its maximum resulting in a relaxation wind up. When the process resumes, the output will not exit its maximum until the measuring point is exceeded, causing large overshoots. This problem can be avoided by including an anti-reset wind up circuit which eliminates the problem of output saturation.

Q. What are the common types of tuning methods?

There are two types first is closed loop method that is  Ultimate gain method and another open loop method viz. Process reaction curve.

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Q. What is the ultimate benefit method?

The term final gain was attached to this method because its use requires determination of the final gain (sensitivity) and final duration. The final sensitivity Ku is the maximum allowable value of gain (for controllers with proportional mode only) for which the system is stable. The final period is the duration of the response with the gain set to its final value.

Q. Who determines my process reaction curve?

To determine the process reaction curve mine, the following steps are recommended. :

• Allow the system to stabilize at the normal load level.
• Put the controller on manual.
• Manually set the output of the controller to the value at which it was operating in automatic mode.
• Allow the system to reach steady state.
• With the controller on manual, impose a step change in the output of the controller, which is a signal for value.
• Record the response of the controlled variable.
• Return the output of the controller to its previous value and return the controller to auto operation.

Q. What is Anti Reset Wind Up?

If the limiter operates in the feed back section of the control amplifiers integral circuit, the controller output will immediately start driving in the reverse direction as soon as the process signal exceeds the set point. This method is called anti-reset wind up.

Q. What are de-saturators?

When, in some processes, e.g. In batch processes, long transient responses are expected during which a constant deviation is present. The controller integral action continuously drives the output to a minimum or maximum value. the  phenomenon is also known as the integral saturation of the control unit. When this condition.

Q. What is the function of electronic PID Controller?

The input of the measurement transmitter is compared to the set point voltage to produce a deviation signal. The deviation signal is combined with the characteristic feed back signal to provide the input for the function generator amplifier. This amplifier output is distributed to the feed back network and to the final output which is 10-50m.a. Signal for the final operator function.

Q. What is proportional action in an electronic PID controller?

This is achieved by adjusting the magnitude of the feed back signal. An increase in negative feed back means less effective gain and thus a wider band.

Q. What are reset actions in an electronic PID controller?

This is achieved by charging the reset capacitor at a rate determined by the value of the reset resistor. The reset resistor is variable, and creates a reset adjustment.

Q. What is derivative action in an electronic PID controller?

Connection of a derivative capacitor in the feedback circuit delays the feedback until the capacitor is charged to a value approaching the amplifier output. This delay is controlled by the value of the derivative resistor. This resistor is variable and forms the derivative adjustment.