Regulator PID very slow to reach the value Point and zeros process Variable when it should not

Hello

I am using a PID controller to regulate the emission of a filament current in an ion gauge, but I'm running into several problems.

The first and less important, are the controller of PID VI takes at least 5 minutes to get the current where it needs to be.  Is it possible to speed this up?

The second and more important, are that the PID controller tends to zero the process variable before you start the process of getting the close process of the target value variable.  This can be seen in the attached VI: I write 5.8 volts voltage filament - something I did at the beginning to try to get the controller PID for the process close to the target faster - value variable but when the PID controller starts to do his thing, he kills the tension before anything, rather than rise of 5.8 V.

The attached VI is a single which has these problems.  VI actual ion gauge controller I've written has the same problems, but in a form even more frustrating.  I have a while loop set up for the filament voltage to where it should be (using a PID controller) first and foremost, then a loop of data acquisition, which also includes a feedback loop in the form of a PID regulator to maintain the filament voltage.  When the second PID controller starts to run, it concentrates the tension that the earlier had set, taking another 5 + minutes to reach the point where we can take data and giving us 5 minutes of false data in the process!

Does anyone know why PID controllers are behaving like this, and what can I do to fix/work with this behavior?

Hello

It seems that PID VI will always be 0 for the first iteration. You can, however, use the advanced PID VI and set up the first iteration in manual mode. After subsequent iterations, you could then define this automatic mode and there will be a transition smoothly. I think this will give you the desired behavior.

-Zach

Tags: NI Software

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