pid autotune

[prolix]

thought I would put the question here as most pids are used on rims and herms and shinny things.

Anyway set my pid to autotune with these setting

SV - 80c
alarm temps- equal to turn it off
Autotune offset - 2c
control output - pid control
input type - pt10.0 (for 0.1c accurracy)


Thing is it got to 80 but now it creeps up to 81 to nearly 82 degrees, and fires the heating even when that high. I assumed that at 80 it would not heat up any more not gradually sneak higher and higher.

Am I missing something or is it just wierd? I will try the other pid and pt100 tomorrow and all four permiatations to ensure it is not a hard ware fault. All are from Auber so presumed functioning, and we know presumption is the king of all calamities.

Any advise would be good.

Cheers.

 

[unclepumble]

Not knowing your PID controller or having read the instructions, this is a bit of a stab in the dark.

Is Auto tune similar to hysterisis, cos if it is the bigger the setpoint value of hysterisis or autotune the larger the operation band either side of the required setpoint, a value of 2 would allow rise in temp to 82deg and a fall to 78 deg.

Therefore if you want to stick at 80 deg i would set the hysterisis to 0.5 deg or less, if your autotune allows you to, set it to 0.5 and try it

Theoretically your heater should cut out at 80.5 deg and come back on at 79.5 deg then.

this would be true for any setpoint so if you want to save time cover your element with cold water and set your set point to 20 deg it will still work the same as at 80deg

UP

 

[craigite]

HI

Just got home a PID and wired it up this weekend. Had a similar experience but found that the system seemed to learn. I take it that the autoset proceedure allows the system to establish the work required. The first time I ran the system the heating element kept going on and off, but now it only switches on and off a few minutes and then gets on with the task at hand. It does overshoot the temp slightly but I've altered the overshoot setting to suit my system.

 

[prolix]

yeah I rechecked the setting and ran it again and this time it behaves, I am happy, there are some things life is too short to ask why over. : :thumb:

 

[Vossy1]

Good to hear it's sorted p :thumb: