PLUS+1 Software > Function Library

PID function block weirdness?


Hi all,

I've got a stability issue with a PID speed control.
I'm trying to use a PI or PID Function block, v4.0 and Ive got some weird behavior:
When I disable the I- and D-functionality by setting the gains at 0, The I still rises when I change a speed set-point from 0.
By using the I-stop I'm able to cut that.  So the I-output and D-Output stay at 0, which is what I want.

But then I've got a next issue: Setting P-gain incrementally higher, results in my application getting stable up-to about 50% of the set-point, further increasing the P-gain, the control (P-Output) starts to oscillate wildly, without the error ever going negative. I would expect an oscillation to start once the Feedback goes over the setpoint, but I'm seeing this way before the first peak-value reaches set-point.

Any Ideas why the P-output behaves so weird?  I don't think there is an issue with overflows on my end of the programming, but a lot of the FB is hidden...


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