Control loop:
The control loop is consist of all the elements necessary to move the final control elements. Each control loop has a specific purpose to control different parameters in the process. A controller gives instructions to an actuator on their action based on the analysis of setpoint and the feedback signal from the process itself. The actuator manipulates the process by a control action.
What is loop checking?
The loop checking is a test to confirm that the control loop is “operating as designed” and then to ongoing programs for benchmarking and monitoring performance.Some think of loop checking as a process to confirm that the components of the loop are wired correctly and is typically something done prior to start-up.
After all installation process and the wire has been done, the control system should perform the intended function properly. This includes verifying the transmitter’s process variable (PV) for display to the operator, for use in the control strategy, and for historical trending.
There are different processes to finish the loop check property, Hot and Cold checking are the process involved in the loop checking.
Cold loop Checking:
In Cold loop checking only the continuity of the connections are checked.
Each of the branch cables is checked for continuity. All the cables from the controllers to the process actuators are checked, ensures that the connection is continuous and it is broke or distortion in the channel.
All the cables from the main cable to interface cables are checked.
Hot loop checking:
After entirely completing the cold loop checking, the entire loop functionality is checked by connecting the loop to any of the controllers and power.
Now we the feedback system is implemented, the process output is feedbacked to the controller system. The controller system is provided with the setpoint and the process output measured by the sensor is compared with the setpoint in the controller.
For that we manually adjust the process output to some known quantity and read the output in the controller, both should be the same.
check out the Basics of Hart Communicator BASICS OF ON/OFF CONTROLLER