Basic Process Control Terminology

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In my Previous video I discussed regarding process control Fundamentals and the link is given in the description below

In todays video I am gonna discuss basic Process control terminology which is very important in instrumentation

The various components that make up a control system are seen in the diagram. Each of these components has its own characteristics, and changing any single component will change the overall response of the control loop.
A simple control loop, shown below, is comprised of six major parts:
Control Variable
Measured Variable
Setpoint
Error signal
Controller output
Manipulated variable
Now we will know what is Control Variable is
The controlled variable is a process parameter being controlled. In the example here, water level in the tank is the controlled variable, but it can be any process you wish to control.
Controlling this variable is the primary function of process control. Controlled variable is indicated with the letter “c.”
Next is Measured Variable:
The measured variable is the electronic or pneumatic representation of the value of the controlled variable.
The measured variable typically comes from a transmitter, which measures the controlled variable and produces an output representative of it.
In the example here, the level transmitter is measuring level in the tank (the controlled variable) and converting that level to a 4-20 milliamp signal. Measured variable is indicated with the letter “b.”

Next is Setpoint:
The measured variable is sent to the controller in the loop, where it is compared to a desired value called the setpoint. The setpoint and the measured variable are compared in order to produce an error signal.
The setpoint is often manually entered by an operator, but it can also be automatically obtained from other systems. Setpoint is indicated with the letter “r.”

Next is Error Signal:
The error signal is the difference between the measured level and the setpoint. It can be either a negative or positive value. The error signal is then added to the base signal level of the controller to create the controller output.
For example, the base, or initial output, value of the controller may be 50% with a zero error signal. Any error signal developed by the controller is then added or subtracted to this 50% base level. Error signal is indicated with the letter “e.”

Next one is Controller output:
The controller output is simply the total output of the controller. With the controller in automatic, the output is calculated by the controller itself.
If the controller is placed in manual, the output can be manually adjusted to any desired position. Controller output is indicated with the letter “p.”

And the last one is Manipulated Variable:
The manipulated variable is the parameter that is adjusted to bring the process back to the desired setpoint.
The manipulated variable in this case is the water entering the tank. The water flow is manipulated in order to keep the level constant as the output demand changes. Manipulated variable is indicated with the letter “m.”