In the previous video, we generated some PID coefficients using a manual tuning method.
Let’s run some tests to see how well it works.
I’ll go to the ISA PID algorithm in the spreadsheet, we want the parameters optimized
for setpoint changes and let’s start with the PI numbers.
I’ll put those in here and let’s use 1 second for the sample time because we know
from the previous video that’s close to what the PI Autotune will give us.
That will give us more of an apples to apples comparison.
You want the sample time to be faster than your process responds.
We’re doing temperature which takes several seconds to respond so 1 second should be fine.
Write them out and make sure we are in Auto Mode.
I’ll bump the setpoint up 5 degrees like we did before, fast forward and the CLICK
PLC automatically adjusted the PID output to get us to the new setpoint quickly and
efficiently.
Exactly what we expect.
I’ll go to 100 degrees like we did before and then back to 110 degrees.
Looks pretty good!
The cool thing about this manual method is it’s an Open Loop tuning. That is, we put the
PID function in Manual Mode, did a 5% bump and took some measurements. It doesn’t
rely on the CLICK PLC's PID algorithm at all which makes it a good independent way to verify
your autotune results because all the tunings we did in the previous videos were Closed Loop. They
actually use the PID function in Auto Mode to monitor the process variable, do the three
cycles, and make a decision.
Which begs the question – how does this manual tuning compare to the autotuning we
have been doing?
Let’s make sure we are in PI mode, do and autotune and let ‘er rip!
I’ll fast forward through that and we see the 3 cycles of the autotuning. Yep, looks
good!
Fast forward through our usual setpoint steps and look at that!
This is the manual tuning, and this is the autotuning.
Our manual tuning is looking pretty good!
OK, let’s try the PI and D version of our manual tuning.
I’ll just take the results from our spreadsheet and put them in here.
And I’ll use one of the sample times we got from an autotune in a previous video
so we have an apples to apples comparison.
Fast forward through our usual setpoints … and look at that. It’s even better
than the PI version!
In general, you will find that temperature PID applications will almost always work better
with the full PI and D coefficient set while just P and I will usually be fine for most
other industrial applications.
OK, let’s compare that with the autotune version.
I’ll select a P, I and D version and let ‘er rip.
Fast forward and we see the closed loop 3 cycle autotune and the new parameters in
the PLC. Looks good. And fast forward through our usual three setpoints.
Well, how about that?
This is the manual tuning, this is the 3-cycle autotune and this is the autotune
result.
The manual tune nails it!
Very cool.
Here’s a look at all four side by side.
PI Manual Tune, PI Autotune, PID Manual Tune, PID Autotune.
Looks like our manual PID tuning is gonna give us the cleanest response for this system.
Let’s put our manual PID coefficients back in and do one more experiment.
We have been changing the setpoint.
Let’s change the load.
I’ll close most of the vent holes on the enclosure which will reduce air flow so we
should need less heater power. Will PID adjust accordingly?
I'll fast forward and yep we see that PID automatically lowered the output to accommodate
the new load.
Open the holes back up and fast forward and PID automatically
adjusted the heater power again to maintain the setpoint.
Perfect.
We did that using the coefficients optimized for setpoint changes.
But we changed the load, so we really should be using these coefficients that are optimized
for load changes – right?
Yeah, well, I’ve never had any luck with those and these work just fine so I use them.
When I do use the load change equations, I get results like this.
Let me know if you figure out what I am missing here.
Anyway, the bottom line is you now have several ways you can tune a PID loop: The CLICK PLC
Closed Loop Autotune PI and PID, and the Open Loop Manual Tune method for P, PI, PID for both Setpoint
and Load Changes and for all three types of PID equations.
How about that?
A couple things you need to be aware of: This manual tuning we did in this video was
for this specific self-regulating type of system.
Don’t assume what we did here will work for all systems and don’t assume my spreadsheet
will work for your system until you have taken the time to understand how the method works.
I skipped some things that I knew weren’t important or required for this demo, but they
might be real important to your system.
Check out the PID Blueprint website to see how to do other kinds of PID systems and learn
more about this method.
And remember – PLEASE don’t call AutomationDirect’s support team about this method. It isn't
an AutomationDirect product, so they can’t support it.
Click here to see the other videos in this CLICK PID series.
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