help to find control system element equation

[joy81]

hello everybody,

i am looking for a little help because i am so confuse. i have a second order transfer function system which i need to model in sumulink. i am making a temperature pid controller. i am using a heating element which is the process. how can i find out the process function/equation? i know how to work out equation from a electrical circuit, but i don't know how to work out the equation for a heating element.


please tell me if it doesn't make any seance to you.

thanks

 

[FeX32]

You don't need to. The feedback can be just the output of the sensor. This should be just fine.
If you really want to model the temp sensor dynamics you can use a first order differential equation like
dT/dt=k*T(t)
The solution is a natural exponential function.
Although, many sensors may behave differently.


Fe (IronX32)

 

[joy81]

thanks for the replay. if i dont know what is my process function how can i find out my 2nd order transfer function?

what i came up with to use the phisical process to see the feedback output. make a graph and use those value to do the transfer function, am i right?

one more thing my input is duty cycle and set point is degree C. how are they related? i can use labview to tune and make the control system in no time, but i need to understand how come the input and set point is two different type, and how can i explain it.

 

[HEC]

Looks like a homework problem, read the site rules!

Mark Hutton