Auto-Tuning Time for JLD612

[Paulsey88]

Hi,
I am using the JLD612 as a temperature for sous-vide. After being absolutely positive my wiring is right, I attempted
to have the jld612 raise the water bath to a target temperature of 100 F...It overshot this target temperature by 4-5 degrees, then held steady ~2 degrees above the target temperature. I then ran the Auto-Tune function so the controller could calculate new PID values. It has been in auto-tune for almost 24hrs. Is this normal?

If auto-tune does not work for my application, does anyone have links to setting the PID values manually for sous-vide?...I am reasonably familiar with PID because I am an EE, but would like to have some help with this. Thanks.

[JHT]

I am in same boat as Paulsey88.
I have not tried in actual water bath yet but when PV is below SV the SSR is cycling on/off in about a 1 second loop.. why wouldnt it stay on until PV is the same as SV? I have just started AT about an hour ago and its still running..
What is AT actually doing? and I would like to know the manual settings as well.

[glassguy213]

I just got the JLD612 and after a little testing here is what I think about the AT feature...
The controller can't perform auto tune unless your system functions properly. In other words if you don't have the controller hooked up to a system that will either heat up to reach a set temp (for heating applications) or cool down to set temp (for cooling applications) then the AT will never be able to interpret the performance characteristics of your system and determine the best parameters. In this case AT will blink forever.

Here is what I did to test my controller and TC (this is assuming an ambient air temp of up to 85 degrees F). Press "Set" and enter 0001 press "set"
Set the SV temp to 89 degrees F
Press and hold the > button until AT light blinks
My room temperature was 72 degrees so the Output light was lit full time (the system was trying to heat up to reach the Set Value (SV) just like it is supposed to except I was not using a heating element).
Wrap your hand around the tip of the thermocouple and the temp reading should begin to rise.
When the temp reaches the set point (actually a degree or two over) the output light goes out.
Let go of the thermocouple and let it cool gradually a few degrees. The output light will come back on.
When the temp is a few degrees under the SV hold the TC again to bring it up to the SV. Let it go and cool again, then hold until set point is reached again.

At this point my AT light stopped blinking because it was able to determine the heating and cooling cycle of my artificial "system". I will have to program again with the real system, but this lets me see that my unit is working properly. The controller is reading the rate of temp rise and the rate of temp reduction to determing how to "ramp up and down" the on/off cycle to avoid overshoot or undershoot. You can see after this that the output light will begin to cycle as the temp gets close to the SV (so if there was a heating element it would be cycling on and off). You will also see when you let go of the TC that when the temp begins to drop the output light will come on intermittently which should be bringing the temp back up.

If you do this test you can verify that your controller and tc are functioning correctly. Be sure to repeat the AT process when you install on your actual system as the controller will need to determine the performance characteristics of your system to reprogram.
Hope this helps

[JHT]

Thanks Glassguy213,

I will give this a try, makes total sense to me, I wish they mentioned this in the manual, if you could call it that..
I guess what do you want for $35

[richiem]

Water bath temp control is always a bit iify, because the system response time is so slow. So playing with the PID parameters is needed. The Manual does indicate the characteristics of each part of the PID system --
-- proportional control, which offers finer control at temps close to the target temp and coarser control when the tamp is far from the set point.
-- integration time, which controls the slope of the temp rise.
-- differential control, which adjusts the response to large step changes, steepening the ramp slope in response to big changes.

For a slow responding system, I think you want the P value to be mid-range somewhere, the I value lower end of range, and D value lower -- for my hot tub I'm using P=5, I=10, D=20. With these values I have essentially no overshoot, and get stable control to within 0.2 degrees when the cover is closed and we're not using the tub. Opening the lid causes a slow ramp down because my 1.5kW heater cannot hold up the temp of the 250 gallons of water when it's cold outside, but it does hold within 1 degree F on even the coldest 20 deg. nights here when I lounge in the tub for 15 minutes or so. Of course, the thermal mass of all that water does help holp the temp up, but it also slows down the heater's ability to heat.

Note also that with a liquid system, the water (or whatever) needs to flow over the temp sensor constantly, which means using a full-time circulation pump -- otherwise, if a pump is going off and on along with the heater, the temp fluctuations will be quite large since the sensor isn't giving an accurate measurement of the actual temp of the bath. My hot tub has a small 24/7 circulation pump.

In a small bath, say 20 gallons, putting the temp sensor directly in the bath, away from side walls, near the middle of the bath will provide a fair sample of the actual temp -- but if no pump is used and the heater is directly heating the bath by conduction, convection currents may be erratic around the sensor, again causing the controller to respond incorrectly to the system.

Some thought is needed for these systems as to the location of the sensor, the heater, and the control settings, and there is no substitute for trying things out.