I have a project where I want to control the power consumption of a machine such that I reach a certain amount of power consumed at the meter.

For current testing I set the setpoint to -5000 (meaning 5000W is to be consumed).

For the process value I expect a value range of -17250W up to 17250W. Above that fuses should blow.

At the time of testing power consumed is measured as approximately 2000kW (process value -2000), correctly shown on the website I made in LWE and stored in VW32.

I use VW32 as an analog input to the PI controller and the PI controller shows PV zero in an online test and does not change the output AQ over time.

Probably something very basic but where do I go wrong?

Ok, but then I still do not understand why a PV of -2000 does not show up when it is inside the range of -10.000 to +20.000 mentioned in that help. Any thoughts on that?

An why does the PI controller not respond when the SP is -5000 and the PV is -2000?

I was aware of the limitation of an AI but since that did get the PI controller to respond I do not see why a VW of with a value of -2000 should not.

I know about the controller being able to work only in the specified direction but does that also mean that it can only accept a PV that is either always negative or always positive?

I mean a PV of -2000 is within the range of -10000 to 20000 right? Why does it show as zero in the PI controller then?

I have started a support request and requested the engineer to respond preferrably here.

Just to experiment: The VW32 I was using as an input was defined as the difference between VW10 and VW12.

Just to make sure that I was not screwing up on the calculation of that difference somewhere I decided to just connect VW12 (with at the time of starting the PI controller a value of about 315 or so) to the PI controller. Then I gave the PI controller a setpoint of 3000.

The controller accepted that value, made 1 jump to something else (I estimate 1000 or so) and the PI controller ramp up to 1000 at the output.

The actual PV then ramped up to nearly 6000 (nearly 5000 at the time of taking the screenshot but the PV at the PI controller keeps showing 1000.

Why you put Gate Not the iput A/M of PI controller function.

This way pay not work you must change or put a digital clock with asychronus pulse generator.

Ok I finally got the controller to respond and -at the moment sort of- doing what I want.

What was the problem: Contrary to what the help file suggests you can NOT just throw PV values with any value in the range between -10000 and +20000 at it. The PV connection in the end also kind-of-clips the input between 0 and +1000. So if you throw -5000 at the controller sees 0. If you send 5000 it sees 1000. If you change gain and offset inside the PI controller the values at which PV is clipped change.

Special point of interest is that the PI controller does not seem to be able to handle any transition through zero as PV at all. With a negative gain (in the PI block) it appear to only accept a negative PV and with a positive gain it only accepts positive PV. Both regardless of the offset.

In order to get it to work I decided to first set gain to 1 and offset to 0 in the PI controller. Then act as-if my PV value has a range of -10.000 up to +10.000 and used an analog amplifier with a gain of 0.05 and an offset of +500. I know my expected range is bigger but this amplitude is clearly bigger than the amplitude of the machine I am trying to control so I guess -fingers crossed- that this should work for me. Now any PV value between -10.000 up to 10.000 is scaled to something between 0 and 1000 and this is something the controller understands. 

I can now play with the setpoint and the machine follows that setpoint. Not exactly but close and stable enough compared to what I was expecting.

I guess I could probably omit the analog amplifier between PV and PI by adjusting gain and offset inside the PI but I now have something working that I understand. For the moment I will stick to this solution.

I tried to upload a demo logo file I used to understand the issue but that is apparently not possible, see the attached image for what I built to understand the problem and how to  solve it.