Has anybody used a Watlow temperature controller?

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I am sure there are plenty of people here that have used Watlow temperature controllers.

We have a thermal chamber that we used to temperature stress circuit boards.
The thermal chamber heats to 85 degrees C. It can go higher. Then it cools to -20 degree C. Again it can go higher. This must be done a certain rates but that is another issue.

The problem is that we lost the parameters. I got the controller going again but the documentation was awful. Not just bad but awful. A P gain should be %output/degree of error. If the gain is a proportional band I expect a number like degrees/100% output. Instead the Watlow seems to be degrees per 1% output.

There can be two sets of PID parameters. One for heating and one for cooling. It appears that the parameters for the cooling PID are set to 0. If so, I assume that I am using the same PID parameters for both heating and cooling.

Is my assumption correct?

Also, our P gain is set to 2.7. I am assuming that means 1% output for every 2.7 degrees of error.

Is my assumption correct?

We set the I gain to 1. We couldn't figure out if this was repeats per minute or minutes per repeat. There seems to be a way of changing between the two modes but we couldn't find it in the documentation.

What is a repeat? What is being repeated? When I am doing temperature PID calculations for PLC PIDs the integrator is usually a time constant, not a repeat.

We have talked about replacing the Watlow with our motion controller. It would be gross overkill but at least we have good documentation and understand how it works.
 
I have done Watlow, but will not be very helpful. My application was reading and writing PID parameters over Modbus but the PID lops were already configured by others.

I agree that manual i awful and I have spent hours digging through it.
If you really stuck try with Watlow support, they are slow in response but may be more helpful.
 
Like chopin, I've used them (10 years ago), but my task was simply to expose parameters to the user / PLC; how to tune them was up to someone else, who probably used the SOTP method of loop tuning. ("Seat-Of-The-Pants").

All I know is that I used a Generic Ethernet module, then (after much work with the manual to determine which ones I wanted), scrolled through an array of SINT(3)s to set Class/Instance/Attribute to get the parameter I wanted associated with which of the 41 I: words in the Generic Ethernet I/O table.

I also built myself a sandbox so that I could do reads or writes of any combination of Class/Instance/Attribute I wanted. I vaguely recall that, once I detected a pattern, there were some parameters that were not in the manual (or at least not clearly indicated) that were very useful. Unfortunately, I don't have any of the spreadsheets or notes that I made at that time; just the code (which is curiously lacking in annotation with respect to the Watlow).

If you've got communication established, you've probably already know this.

Good luck.
 
There can be two sets of PID parameters. One for heating and one for cooling. It appears that the parameters for the cooling PID are set to 0. If so, I assume that I am using the same PID parameters for both heating and cooling.

Is my assumption correct?

Also, our P gain is set to 2.7. I am assuming that means 1% output for every 2.7 degrees of error.

Is my assumption correct?

We set the I gain to 1. We couldn't figure out if this was repeats per minute or minutes per repeat. There seems to be a way of changing between the two modes but we couldn't find it in the documentation.

What is a repeat? What is being repeated? When I am doing temperature PID calculations for PLC PIDs the integrator is usually a time constant, not a repeat.

We have talked about replacing the Watlow with our motion controller. It would be gross overkill but at least we have good documentation and understand how it works.

Based on experience with the Watlow 96 controllers, here are some answers to that series:

. With dual output, heat/cool PID controllers, one set of tuning constants apply to one controller output, and the other to the second output.
. Units of PID parameters depend on whether the controller is in US or SI mode. This is set in Setup/Global Menu, parameter Unit.
. Watlow seems to use Proportional Band in a non-typical way since it is specified in engineering units instead of percent (US setup). This would imply it is inverse of Proportional Gain, and maybe as input value per 1%.
. "Repeat" traditionally referred to repeating the proportional action, and implies interacting P, I, and D action. In the case of integral action, it is often called "reset" because it is equivalent to someone resetting a P-only controller. The specified time value is how often the controller automatically resets, repeating the P action. Of course, this is happening continuously and not bumped at the reset time.
. With the SI setup, the Watow 96 unit for integral control is minutes per repeat, implying it is like Integral Gain, but the "per repeat" is a red flag that it may interact with the proportional action, as opposed to being independent.

These low cost single-loop controllers tend to be poorly documented, and inconsistent in their expression of the PID computation. Manufacturers seem to think everyone will just use the built-in auto-tuning, and not try to model and calculate gains. Watlow is no exception.
 
its been 6 years, but I do remember that watlow has a programming package that will do what you want in one software routine (our controller did, cannot say if yours does or not).

all you need is the set of conditions for your test.
for example.
1. from room temp, ramp to 85 deg c in 30 minutes.
2. stay at 85 deg c for 1 hour
3. ramp down to -20 deg c in 45 minutes.
4. review your steps and save program to hard drive (we also put it on our network).

then use the software to program your steps and download into the controller.

regards,
james
 
Your welcome gentlemen. Learned plenty from both of you. Glad to contribute in return when I can.
Used it years ago when I was a bit confused about PID.

Credit goes to Watlow for writing something practical about PID that normal people can understand.
 
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