Question

What is a PID/Process controller?

Answer

This type of feedback controller has a single-loop (one channel of control) and utilizes a PID (proportional-Integral-Derivative) control algorithm.
The output (control variable or CV) of this controller is based on the error created by a user defined set point (SP) and a process measurement (process variable or PV).

The PID algorithm defines how each element acts on the error signal created.

Proportional

• The proportional term simply responds proportionally to the current size of the error.
• The loop controller calculates a proportional term value for the PID calculation.
• When the error is zero, the proportional term is also zero.

Integral

• The integral (or reset) term integrates (sums) the error values.
• Starting from the first PID calculation after entering auto-mode, the integrator keeps a running total of error values.
• The running total represents the constant output required to hold the current PV.

Derivative

• The derivative (rate) term responds to change in the current error value from the error used in the previous PID calculation.
• Its job is to anticipate the probable growth of the error and generate a contribution to the output in advance.

---

FAQ Subcategory: None

This item was last updated on 2021-02-18
Document ID: 921

---

The information provided in the AutomationDirect knowledge base is provided "as is" without warranty of any kind. AutomationDirect disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall AutomationDirect or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if AutomationDirect or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion of limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.