We have a weigh feeder ( belt conveyor) in our plant which charges calcine at a fixed flow rate. Its rpm adjusts itself automatically wherever there is a change in loading of calcine on it. How can we relate it with process dynamic control? How to determine the order of the system?

Sorry but it didn't answer my question.

I wonder if you could run a test of the system in open-loop to determine the response order. If you could plot flow rate versus rpm, you would likely yield a first order response. I have not learned much of the controller part yet but hopefully you could find which tuning rules it uses.

Sheikh,
Using a simple "thought experiment" it seems that this is a simple first-order system: as the loading on the belt changes, the controller adjusts the drive RPM to maintain the flow SP. I suspect that the calcine loading on the belt is subject to frequent disturbances. As a result, observing the exact nature of the process characteristics is probably quite difficult, hence your question.

As Joe suggests, if you are able to place the controller in manual and perform a step test, you should be able to quickly assess the order & dynamics of the process. The "trick", of course, is to make a change to the RPM that is large enough to move the flow rate outside the noise of the loading disturbances, but not so large as to cause undue disturbance to the downstream processes. If you have the ability to affect the calcine loading on the belt, it may be worthwhile to look at that aspect first in order to reduce/minimize the disturbances to the calcine flowrate. Once that is done, then you can perform the step test using a smaller step change.

use VFD (variable Frequency Drive) and connects weight feeder motor to your DCS..

Sheikh, your question is maintain Fixed flowrate , now the dynamics of time v/s RPM indicates, If the weight on the feeder is reduced you need higher RPM to keep the same flowrate of calcine. hence relating the RPM, Weight and Time are three variables. Controlled variable is RPM and measured variable is Weight. Apply polynomial first order equations