Glossary of Control Engineering Terms - I

I/O: Input/Output. Refers to the electronic hardware where the field devices are wired. Discrete I/O would have switches for inputs and, solenoid valves and pumps for outputs. Analogue I/O would have process variable inputs, and controller outputs.

Identification (System): The process of collecting input and output data (time or frequency) from a plant a fitting a dynamic model to represent the output response and hence hopefully the plant.

Integrating Process: With these loops, making a small change in the controller output will cause the process variable to ramp until it hits a limit. The larger the change, the faster the ramp. Also the smaller the integral time the faster it will move. It is a common misconception that integral time in the controller is not required to hold setpoint with an integrating process. However, using integral action with an integrating process can lead to an unstable system. Integrating loops are also described as non-self-regulating, where a change in the actuator (when in manual/open loop) causes the process variable to move and keep moving (until it hits a limit!!).

Integral Action: The "I" part of the PID controller. With integral action, the controller output is proportional to the amount and duration of the error signal. If there is more integral action, the controller output will change more when error is present. If your units on integral are in "time/rep" or "time" then decreasing your integral setting will increase integral action. If your units of integral are in "rep/time or "1/time" then increasing your integral setting increases integral action.