Honeywell Udc3300

Can Anyone Tell Me How To Set A Honeywell Udc3300 Temp. Controller To Continuly Tune It Self. I'm Using It To Ramp Down To -285f And It Seems To Over Shoot The Sp. On The Way Down. Once It Warms Back To The Sp. It Holds A Steady Temp. It Is Setup In Pid-a Mode. Thanks For Any Suggestions.

Are you trying to control at more than one setpoint? The PID parameters will be different for -285 vs room temp. You may need to use dual PID. Accutune II has a Fuzzy Logic option to help with overshoot. This is what you may want to activate.
Check out the 2 links here:

http://content.honeywell.com/ipc/faq/pdf/934701.pdf
http://content.honeywell.com/ipc/faq/pdf/934601.pdf

All the Tech Tips from Honeywell are here:

http://content.honeywell.com/ipc/faq/CONTROLLERS-UDC3300.stm

There Are 4 Ramp Down Steps And A 1hour Soak Time Between Each.

Try the dual PID option first. It's promoted as a feature so you can have one PID for heat, and the other for cool, but it doesn't matter. The controller will switch to a different PID based solely on a setpoint.
Tune the second PID at -285F. Switch to the second PID about 5-10% into your last rampdown. You don't want it to switch PID parameters at a setpoint, or it will 'hunt'.

Fuzzy Logic was the wonderful new thing that was going to save the world, but it didn't turn out that way. Some are better than others, but most will agree nothing can replace a well tuned PID.
Try it to see if it helps, but don't be surprised if it's not perfect.

You can't always trust Autotune. Use it to get numbers close, but don't be afraid to do a little manual adjustments to get it perfect.

You want to initiate autotune on an approach to the final setpoint, for your case, when ramping down. Is that how you've done it in the past?


Dan