Determining Transfer Function of Real World Systems

Greetings All,

I've recently developed an interest in process control, so I'm quite fresh - bare my illiteracy -

I would like to get some guidelines of where to start, what experimental data do I need to gather in order to determine a Transfer Function with the aid of Matlab/Simulink.

Scenario: I have a heat exchanger with steam coming in, cold fluid coming in, condensate coming out, hot fluid coming out.

a) what kind of real data do I need to gather to start?

b) what tools in Matlab that will help me to determine Transfer Function using data from (a)?

Thanks All

[David K.]

The answer to a is really only something you can answer. What is it that you find to be important with your system? A basic transfer function has 1 input and 1 output. You can handle more but Im going to assume it is SISO for now. The input you choose will want to be one you can control pretty well.

The easiest way, to me, to find the transfer function is using matlab pidTuner. They, when in the gui choose your plant by selecting to identify a new plant. Most likely you want to look for something called the step response. After you have chosen your input and output signals, start measuring with the input off, then turn it on to some value and wait for an amount of time representative of your system. You can take that input and output data and put it into the system identification to start fiddling around to find a transfer function that fits.

Apparently there is another gui brounght up by systemIdentification but I have never used it.

[Star Strider]

System Identification Toolbox

[aljawada13]

How to aqquire data that I need to import in System Identification? I have controller measured inputs and outputs in terms of %, where to go from there?

Answer 1

[Priyanshu Mishra]

For modelling a heat exchanger, I would suggest you to install system identification toolbox. For data representation you can use iddata. To estimate the transfer function of heat exchanger, follow the steps explained in the following link

https://www.mathworks.com/help/ident/examples/estimating-transfer-function-models-for-a-heat-exchanger.html

[aljawada13]

Thanks!