RSLogix5000 PIDE implementation

Hey all!

I am using a PIDE (and indeed an FBD logic) for the first time. I have two questions.

1. I am running PIDE to speed control. Speed is bi-derectional so it can be +ve or -ve speed (+6000rpm to -6000rpm). Can a PIDE output a +ve and -ve CV, depending on the setpoint? The output is going to an Analogue output card (+10V to -10V).
2. I am trying to play around with switching between auto and program (program) mode so I can set program to output CV=0 when PIDE need not run so it suffers no wind up. I have not implemented the switching between modes yet, but if you see in the attached image, I cannot even get an Auto=1 output when I feed 1 into ProgAutoReq. Have I fundamentally got something wrong?

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I appreciate any guidance from those with a bit of FBD and PIDE experience.

Cheers,

Ben

1) use your PIDE output (0 to 100%) as your input to a scale instruction, scale output is going to be -10V 0 10 V, then move this output to your analog module.
2)It is best explained by Ron Beaufort papers, go to his web page.
Send me a pm i got them, they're too big to be shown here.

widelto said:

1) use your PIDE output (0 to 100%) as your input to a scale instruction, scale output is going to be -10V 0 10 V, then move this output to your analog module.
2)It is best explained by Ron Beaufort papers, go to his web page.
Send me a pm i got them, they're too big to be shown here.

Click to expand...

Thanks very much, greatly appreciated. Will pm you now.
Cheers.

your original post makes it look like you're confusing TWO separate things:

(1) the STATES ... Program State ... Operator State ...
(2) the MODES ... Auto Mode ... Manual Mode ... Override Mode ... Hand Mode ...

I'm working overtime on some special projects – so I don't have time to go into too much detail – but here are some basic ideas that might help ...

for PIDE there are two "STATES" ... (1) the OPERATOR state ... and (2) the PROGRAM state ... you have to decide which of these two "states" you want to use ...

as shown in the figure below, your "ProgOper" pin has a ZERO output – which tells us that you (intentionally or otherwise) are currently in the OPERATOR state ...

in the next post I'll attach a PDF page that I designed for use in my classes that should be helpful ... the figure below shows some excerpts from that page ...

(a) suppose that you decide to go into the Program State (the PDF will show how to do that) ... while in the Program State you would need to make the following settings (as shown in Column I) in order to get into the Auto Mode ...

ProgHandReq must be held at ZERO ...
ProgOverrideReq must be held at ZERO ...
OperManualReq is a "don't care" – as shown by the X ...
OperAutoReq is a "don't care" – as shown by the X ...
ProgManualReq must be held at ZERO ...
ProgAutoReq must be held at ONE ...

again IF you're in the Program State - those settings should get you into the Auto Mode ... .

now then ...

(b) suppose that you decide to stay in the Operator State (the PDF will show how to do that too) ... while in the Operator State you would need to make the following settings (as shown in Column N) in order to get into the Auto Mode ...

ProgHandReq must be held at ZERO ...
ProgOverrideReq must be held at ZERO ...
OperManualReq must be held at ZERO ...
OperAutoReq must be held at ONE ...
ProgManualReq is a "don't care" – as shown by the X ...
ProgAutoReq is a "don't care" – as shown by the X ...

again IF you're in the Operator State - those settings should get you into the Auto Mode ... .

I hope that this helps ... good luck with your project ...

.

here's the PDF which I designed to show the "states" - and the "modes" ... incidentally, this particular page is not included on my website ... I use it in my classes on PIDE ...

.

Ron, what a gent, thank you. I am trying to dissect now and will hopefully implement today, will feedback on my progress.
Cheers,
Ben

Ok, this should get me into the Program State, Auto Mode. You can see that the ProgOper oin is still zero, although this is all offline currently. Stupid question, but do I need to be online for this pin to change state, or should it know its state based on the current input pins state?

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Thanks,

Ok, I think I have resolved the issue now, I needed a JSR from the main routine to the PIDE FBD routine.

Yes- you need to be online and have a JSR. Also (you may already know this), if you go in the "parameter" settings of the PIDE, you can manually enter a 1 for lets say "ProgProgReq" and save. Then you will not have to have it external on your FBD.
The good- frees up space especially if you have a lot of tiebacks and things going on.
The bad-harder to remember what you actually had set to 1 or 0!

Thanks dginbbuffalo.
Can anyone explain in reasonable terms exactly how the PIDE reacts vs the PID with respect to Proportional Gain only? As I understand, for PID Proportional Gain x Error and the PIDE Proportional Gain x Change in Error. So what happens with equilibrium, does it see no change in error and then shut down CV to zero? So then the next update there is no CV, so the PV drops or increases and so we get a change in error. So the system 'pants' at equilibrium?

OK, have just read up a little. It seems that the PIDE incorporates CV(n-1), but this is based on integral accumulation only. Am I correct in saying that you have to have some integral and so cannot run PIDE as a Proportional Only controller, like you could with a PID instruction?

http://literature.rockwellautomation.com/idc/groups/literature/documents/wp/logix-wp008_-en-p.pdf

I really don't think they work much different than each other in most instances. Check out the link if you haven't seen this already. It explains the differences and states "Understand that both a positional form and a velocity form PID
algorithm perform identically in response to a change in error".

Also very informative in other areas of the PIDE abilities.

Thanks, I already have that pdf, it is quite nice. But it doesn't really 'spell it out'. I'm inferring from the equations for 'positional' vs. 'Velocity' algorithms. shown at the bottom of page 2 and top of page 3. It would appear that at time=0 of running the loop, there is no change in error, nor a previous CV value, so it cannot work a Proportional only controller, at least immediately. So I think that maybe it has to be a PI controller as a minimum, am I correct in this assumption?

bgtorque said:

Thanks, I already have that pdf, it is quite nice. But it doesn't really 'spell it out'. I'm inferring from the equations for 'positional' vs. 'Velocity' algorithms. shown at the bottom of page 2 and top of page 3. It would appear that at time=0 of running the loop, there is no change in error, nor a previous CV value, so it cannot work a Proportional only controller, at least immediately. So I think that maybe it has to be a PI controller as a minimum, am I correct in this assumption?

Click to expand...

I know what your saying, but i do not think that is the case. I believe most of the times i used the PIDE, I started with a Proportional only loop, and then while tuning, I added Integral.

Velocity PIDs can't work in proportional only modes. The integrator is required.