Controllers | Configuration of a controller

Table of Contents

Instrumentation Instruments & automatic controllers are generally grouped at one location near the processing unit or manufacturing operation which they serve. Actually the fundamental purpose of Instrumentation is control of production quality or quantity.

A controller is a device which automatically regulates a controlled variable

Configuration of a controller:

Above Fig shows a typical Electronic controller configuration. Different types of controllers have different configurations but they are all basically the same.

FUNCTION OF EACH UNIT-

Each Unit has separate function that is given below-

1.Set point Transfer:

Transfers between the local set-point signal from the manual setting unit of controller and an external set –point signal ( cascade )

2.Manual setting unit:

Generates a set point signal for a local setting.

3.Set point Indicator:

Indicates either the local or the cascade selected setting value (SV )

4.Input signal Indication:

Indicates the input signal (process variable PV corresponding to controlled variable)

5.Deviation detection:

Calculates the deviation, the difference between set- point and input signals.

6.Direct-Reverse Transfer:

Transfer between direct and reverse action.

7.Direct (Increase ) Action:

Action of a controller where the value of the output signal increases as the value of the input (process variable ) increases.

8.Reverse (Decrease ) Action:

Action of a controller where the value of the out put signal decreases as the value of the input (process variable ) increases.

9.A/M Transfer:

Transfer between Auto and Man.

10.Output balance-less- bump-less transfer:

If both output are not equal at the time of transfer from auto to manual or manual to auto., the output will change in steps when the transfer occurs. This is called a bump and it is undesirable as it disturbs the process. Therefore, a balancing operation is required to avoid this bump. An automatic balancing operation enables the bump-less transfer without a manual balancing operation. This transfer is called a balance-less – bump-less transfer.

11.Output Amplifier:

An electronic controller is equipped with an output amplifier to output a 4-20 m A DC current signal.

12.Output Indicator:

The output signal is indicated in units of 0-100%. When a control valve is driven, the output indicator shows the valve opening. Whether 0 or 100% of output corresponding to an open or closed valve is shown on the output indicator.

13.Power source:

Sometimes DC Power supply (mostly DC24 V ) is used instead of AC to back-up the AC power failure .

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