PID temperature controller works slowly

[nishn]

Hi 

I am using a PID controller to control the temperature of a thermal chamber. The problem is that when I plug the controller and turn it on for the first setpoint it takes a very long time for the controller to reach that set point. The problem is worse when the setpoints is close to the room temperature because my gains are smaller in low temps. My guess is that controller resets the initial condition of the Integral term to zero every time that I unplog the controller. Any idea how to solve it and what could be the reason? Thanks. 

[AnalogKid2DigitalMan]

It sounds like this is a stand-alone controller and does not involve LabVIEW in any way?

If so-

What is the make/model of it?

Have you tried auto-tuning?

How fast does the chamber attain temperature starting from ambient if the output is set to 100%?

-AK2DM

[nishn]

Thanks for the reply. It is an Ez zone express controller from watlow. I used its auto-tune to find the gains. Although I think the auto-tune of the controller does not work well in low temperature but it does not seem that the problem is just from the bad gains. with the same gains it works well for the second time. For example if the room temp is 25 I turn it on (plug) and set the set point 45 degree it take 20 min to reach it but now if I give the set point 25, wait for it to cool down to 25 and then the same set point 45 it takes 3,4 min to reach it. It is interesting that if I leave the controller in auto mode, unplug and then plug it back it does not show this behaviour but if i put it on off mode, unplug and plug back ,put it on auto mode again it takes time. 

[AnalogKid2DigitalMan]

That is a bit odd.

I've used a few different models of Watlow's (and various other manufacters) of PID controllers and have never saw an issue like this.

I did come across a bug in an Omega heat/cool controller that had the algorithms/outputs reversed for heat and cool. Talk about 2 days of head scratching....

One thing to try is to do another autoune and make sure the chamber is at ambient before you start it.

You may want to contact Watlow directly regarding the issue for futher and more knowledgable assitance.

-AK2DM

[nishn]

I actually talked to the watlow guy but no useful answer. They just said dont put it on off mode when turn it off. I know that this model does not have the bumpless transfer could it be the reason?

Thanks