Controller won't auto tune

[mheadroom]

Hi all. I have a 612 and setup my system last night.

controller to SSR to food warmer using pt100.

Evernything seems to be working good excpet I keep getting over shoot by about 1.5 degrees and the system flucuates about 2 degrees.

So I figured I would run auto tune. I hold down the ">" button and nothing happens. Do I have to have something set correct for autotune to work? Maybe be in a menu? Maybe a bad controller?

Please let me know. Thanks!

[richiem]

If you haven't chosen the Pt10.0 setting for Inty, do that -- you'll get tighter control at the low temps in a warmer. That said, I don't think that the variations you're getting are large -- a lot depends on a multitude of external factors, especially on the size of the heater element and the heat loss in the warmer; a small wattage heater and lots of area exposed to ambient will make the system very slow to respond and highly subject to air currents and ambient temp changes. Also, the placement of the probe is critical to good results -- try different locations in the warmer and see what happens.

Check your connections, especially for the probe -- see the manual for the right connections -- red to 8, one blue to 9, other blue to 10.

But, if the settings you've chosen actually result in some measure of control, and you hold the > button down for four or five seconds and you don't get the blinking AT in the display, then I suspect the controller has a problem.

[mheadroom]

I double checked the connections. The setup has a lid and temp loss seems faily sslow to me. It just keeps over shooting. The SSR kicks on when temp is 0.2 degree below setting. It stays on until set temp is reached (~100 Seconds). over the course of the next 100 seconds, the system overshoots by 1.5 to 2.5 degrees. Then creeps back down over the course of 25-30 minutes. I checked all the setting and everything looks good. Still can get the autotune to work no matter how long I hold the > button. Guess I need to get it swapped.

[richiem]

The long run-up to temp then overshoot suggests that there is a lot of mass heat storage in the warmer (pan? crockery? glass?) that's taking a long time to get the heat increase out to the probe. This situation will always increase overshoot, which suggests that auto-tuning to increase the I parameter will help....

But don't so anything until you get a working controller.