Discussion Forum

Hi,



Can you try with adding a heaviside function as below:


1500*flc2hs(150-maxop1(T),5)


You can find the meaning of flc2hs in COMSOL manual. The value 5 above is 5 degree Celsius but it is better to remain close to zero such as 1 or 2 degree C, whichever gives you less hassle.



Suresh

Hello,

I have done a PID heater controller based on the library tutorial PID.

It works quite well, but I can't limit the input power to a certain value, meaning that my resistor temperature can jump to 10000K. I have try with lots of tips (contraints on the resistor temperature, 2 PID controller (one on the charge, one on the heater), power limit for the voltage input) but always I have some convergence problems when I try to constraint on the temperature or the limitation doesn't work at all when I limit the input power.

I attach my model version 4.4

Julien

Hi Suresh,

Thanks for the suggestion - I plugged in the heavyside function(s) but it's not really controlling, it just ramps to a steady state value based on how much cooling is applied. Less cooling = higher steady state temperature - significantly above 'setpoint' by >100C in certain situations. The control point is the max value of the heat source, so it's not residual heat from the heater migrating.

Thanks,

Geoff

Hi,



Ok, I see your point. This issue is more to do with controls, such as the PID approach for stability. Perhaps you could look at Julien's mph file above, I don't have appropriate license.

I can only suggest that you write to COMSOL support if they have a nice example on temperature control PID. I think it is to do with the tuning of the PID equation.

Or if you want the crude approach as you originally thought such as introducing some simple logic, I think there could be a possibility by keeping track of history of maxop1(T). For this you need to use time discrete solver which allows you to remember last time step value of the variable maxop1(T). You can then introduce a few if statements; see if you can come up with a logic. But the only constraint with the use of time discrete solver is that the time step is fixed.

I am not at all sure if this works, sorry, may be others can help you because I don't have the required experience.



Suresh

Dear colleague,
I desire to implement a temperature control in my 3D MODEL. It consists the physics coupling between heat transfer and electric currents. The electric potential V is controlled such as the maximum temperature is below 100ºC. I tried to use the maxop1 operator with the sintax 14*(maxop1(T2)<100[degC]), where 14 is electrical potencial (14V) and T2 is temperature variable, but it not is work: the temperature grows without control. I use the time-dependent solver relative tolerance equal to 1e-4 (to properly resolve the switching conditions).
I'm using COMSOL MULTIPHYSICS 4.0
I await help.
Best regards

Cleber da Silva Pinheiro

Hello Cleber,

We of course first suggest that you upgrade to the latest version, COMSOL Multiphysics 5.1, available to all on-subscription customers.

Once you've done so, you'll find the following article about modeling a temperature controller helpful:
www.comsol.com/blogs/implementing-a-thermostat-with-the-events-interface/

Best Regards,

Dear colleague,
Does the version 4.0 not solve the control temperature/electric potential??


--
Cleber da Silva Pinheiro

Dear Cleber,
My comment was more of a general encouragement to upgrade to the latest version. It has been several years (and some minor revisions to the GUI) since version 4.0, but you should be able to follow these instructions equivalently.
Best