PID "Portability" problem

[Autodefenestrator]

I'm currently doing some driver creation in advance of getting actual hardware hooked up.

One of the things I have to do is use a TEC temperature controller.  This will be used on multiple stations with identical functionality, but we sort of "scrounged" for instruments, so we couldn't get the same model of TEC controller everywhere.  We have 3 different ones (Newport 3700, Keithley 2510, ILX LDT-5980 if it matters).

What I'm trying to figure out is if the PID constants that can be set on these devices are universal or not.  They'll all be using the same sensor (10K thermistor) and the same TEC (with adapters for the different plugs), and theoretically they'll all be using voltage set points to drive the TECs.

Basically, I would like to tune the PID for one setup, and then just be able to copy those values over to setups using the other two TEC controller models.  But right now I can't tell if those PID constants are equivalent across all of the devices or not.

[ned]

I took a look at the manual for two of the three - the Newport and the Keithley - and from the (lack of detailed) information there, the best I can say is that there's no way to tell from the documentation whether the gain values have the same meaning for those two. It's possible but I'd say unlikely that you can copy the gains from one controller to the other and get the same results, unless it turns out that they all use the same OEM controller component internally, which wouldn't be unheard of. To determine compatibility, at a minimum you'd need know the units of the controller gains - for example, is Ki relative to minutes, seconds, ticks of the controller's internal clock, or something else entirely? I don't see that information in the manuals.

[Bill Gilbert]

If response time isn't important, you can probably use non-aggressive settings on all that will get to the right temp eventually, but the design of the controllers and their implementation of PID can be very different.

Or, you could do the PID in Labview and just use a power driver driver module for each loop. I did a test stand several years ago running 14 TEC temp control loops using homebuilt current driver amplifiers and an MCC USB-3105. I discovered later that Velleman makes a nice little DC input to PWM power driver kit for about $20:

http://www.jameco.com/z/K8004-Velleman-DC-to-Pulse-Width-Modulator-Kit-Control-DC-Motors_120539.html

Or you could use a DIO output driving MOSFETs or solid state relays for slow PWM (aka time proportioning). I wrote a LAbview time proportioning vi that will do a nice job with cycle times of 1 sec or greater, especially with the 1mS resolution offered by the Wait mS Multiple function since Windows 7. I can send or post if you like.