# Why industry choose PI rather than PID or PD?



## Heartnet (Jul 23, 2012)

Hi,

Why does the industry prefer to use PI rather than PID or PD? Is it because of the reasons below? Please let me know if my theory / finding is wrong.

- Easier to tune
- Easier to implement
- Save time
- D is difficult to find
- D slow down performance
- D creates slight oscillations.


----------



## ScooterMcGavin (Jan 24, 2011)

Derivative is probably the least understood of all the controller functions. One of reasons being is that it often has an opposite effect on the controller output and acts as a "brake" to the Proportional and integral output which often confuses people. I have heard many times " Oh don't use derivative its more trouble than its worth." In many control loop scenarios you can tune a loop reasonably well and get away without the use of derivative. Although with proper use of derivative you can use more aggressive settings on the P and I terms and get where you want to go a little quicker. Process noise can cause oscillation as a result of the derivative action.

From my experience your on the right track with your perception of the general industry use of derivative. There are certain industries where derivative is essential in restraining processes which can result in runaway reactions if not properly controlled. But for you everyday temp/flow/level/pressure control it seems that derivative is often left out.


----------

