Linear Analyzer: PID + Valve with delay

Hello,

I am using the Linear Analyzer to analyze a simple PID + valve system and am facing the following issue. The plant is a 1st order with time-delay valve.

The fig. shows the points where the Open-loop input and output were placed and the step-response plotted. The step response looks normal on the scope, but looks to be linearly increasing and unbounded, in the OPEN LOOP step-response obtained in the Linear Analyzer.

The scope does show the same response if I open-loop the simulink model. So is this is normal?

Answer 1

[Siddharth Jawahar]

Hi Rajesh,

From the screenshot it looks like the linear analysis points have been set up incorrectly. The open loop output should be setup on the outport of the plant subsystem. Having the current set up, you are linearizing the controller. The resultant linear model for the controller, for a step response of the error signal would be a ramp as you see because of the integral property of the PID controller.

If you would like more information to see how linear analysis points work, please check out this documentation:

https://www.mathworks.com/help/slcontrol/ug/specify-model-portion-to-linearize.html?s_tid=srchtitle

HTH,

Sid