When to use PD control system?


#1

The general rule for probably 80 to 90% of the control loops is that P and I action is good enough. Here, during a Setpoint change, P gives you the necessary initial kick while I brings you in to Setpoint through a smooth landing.

So the question is where and how to use D. This can be coupled with when and how to use different forms of the PID equation. Knowing these 2 pieces of information (among others) helps you grasp issues such as slow time to stability or poor response during disturbances,

First D, understand that its a “Derivative” aka a rate of change of PV over time implying the higher the rate of change of PV, the greater the D impact on the Output. As a result, it acts well to prevent PV overshoot or to help kick a slow process.

PD Controller use only when we want very fast action SP=PV…but we cant get bump less action in control valve.

PD control, is under certain conditions a very acceptable solution. It provides rapid response with little or no overshoot. Typically used on large non-symmetrical Integrating processes such as furnaces, space heating etc. There will be inherent offset but that is not always an issue


#2

I love the way you explain it.

To share more information about PID with fellow members, I recommend an article here http://motka.com.sg/media/newsletters/NewsletterJune2016.html
Hope it helps someone.