What is Process Control System

This article is going to be explain for process control system for instrumentation , process and control engineers, supervisor and technicians.

What is Process control system

Control system of the processes within the plant is an important a part of the plant operation. In case of boiler control , There should be enough water within the boilers to act as a heat sink for the reactor however there should not be water flowing out the highest of the boilers towards the rotary engine(Turbine). The level of the boiler should be unbroken
within a precise range. The heat transport pressure is another important parameter that has got to be controlled. If it’s too high the process system can burst, if it’s too low the water can boil. Either condition impairs the ability of the heat transport system to chill the fuel.


Consider a typical process control system. For a selected example let us have a look on open tank, that provides a process, say, a pump, at its output. The tank would need a supply to take care of its level (and so the pump’s positive suction head) at a fixes set and predetermined point. This predetermined level is named because the setpoint (SP) and it’s additionally the controlled amount of the process system.

Clearly while the inflow and outflow must have in mass balance, the level can remain constant. Any distinction within the relative flows can cause the level to vary. however, will we have a tendency to effectively management this process to a relentless level?
We should initial determine our variables. clearly there can be variety of variables in any control system, the 2 during which we have a tendency to most interested are:

  • The controlled variable – in our example this canbe level.
  • The manipulated variable . the inflow or outflow from the system

If we glance additional closely at our sample control system in figure, assumptive the level is at the setpoint, the inflow to the system and outflow to the balanced. clearly no action is needed while this established order exists. Controlling action is just necessary once a difference or error exists between the setpoint and also the measured level. looking on whether or not this error may be a positive or negative quantity or value, the suitable control correction will be created in an effort to revive(restore) the process to the set point.

Hence, the error is always shown as

Error = Setpoint . Measured Quantity

e = SP – M

Control system

The control system action are going to be either to change the inflow or outflow from the system so as to stay the level at the setpoint. allow us to contemplate the general format for achieving these objectives.

How to consider closed loop

As is seen from Figure, the process control system is shown by a closed loop. The system output (level) is monitored by a process sensing element and also the measurement signal is feedback to a comparator at the input of the system. The second input to the comparator is that the setpoint signal; the comparator’s output being the difference or error signal. The electronic equipment, a present simply a recorder, can give the suitable correction to maintain the process at its setpoint despite disturbances that will occur.

How to open loop works

It is seen that if the system were being operated in manual controlling the feedback path wouldn’t be available. The operator would offer this feedback and apply the mandatory correction to the system while observing the result on the controlled variable. this can be termed open loop operation.

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