Here the error is the difference between the set point and process variable (i.e., e = SP – PV). Proportional control or simply P-controller produces the control output proportional to the current error.

Programmable Logic Controllers (PLC) for Industrial Control.

SCADA Systems for Electrical Distribution.

In order to achieve the precise control, most industries use the PID controller ( or PI or PD depends on the application). So the output will be of oscillating in nature. In case of ON-OFF controller, two states are possible to control the manipulated variable, i.e., either fully ON (when process variable is below the set point) or Fully OFF (when process variable is above the set point).

Proportional-Integral-Derivative Controller.

On the other hand, in automatic control, measurement and adjustment are made automatically on a continuous basis.Īll modern industrial controllers are of automatic type (or closed loop controllers), which are usually made to produce one or combination of control actions. In manual control, the operator may periodically read the process variable (that has to be controlled such as temperature, flow, speed, etc.) and adjust the control variable (which is to be manipulated in order to bring control variable to prescribed limits such as a heating element, flow valves, motor input, etc.).

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This is also called as closed loop feedback control system. So the PID controller continuously varies the output to the actuator till the process variable settle down to the set value. This deviation of actual value from the desired value in the PID control algorithm causes to produce the output to the actuator (here it is a heater) depending on the combination of proportional, integral and derivative responses. Assume that the measured temperature from the sensor is 50 degree centigrade, (which is nothing but a process variable) but the temperature set point is 80 degree centigrade. Suppose the process has to be maintained at 80 degree centigrade, and then the set point is 80 degree centigrade. In order to measure the process variable (i.e., temperature), a sensor is used (let us say an RTD).Ī set point is the desired response of the process.

Assume that the process variable is temperature (in centigrade).

Consider the typical control system shown in above figure in which the process variable of a process has to be maintained at a particular level.

Labview pid valve control