How long does Auto Tune take?

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How long does Auto Tune take?

Postby erinh » Fri Dec 10, 2010 2:02 pm

How long should the auto tune light continue to blink? mine has been going for an hour?!


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Re: How long does Auto Tune take?

Postby Tech_Marco » Fri Dec 10, 2010 7:19 pm

Sometime it takea an hour, but sometimes it may take 10, 12, 16... it all depends oon the location that you settle the controller. Let it runs there over night.

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Re: How long does Auto Tune take?

Postby glassguy213 » Mon Jan 03, 2011 6:41 am

There is no set amount of time for AT function but I can complete it in less than 5 minutes. You need to observe whether your system is able to respond to the settings. For example if you are heating and your PV (actual temperature) never reaches the SV (set value to turn off your heater) then AT function can never detect your system characteristics. Your SV is higher than your heater is capable of reaching (or lower if cooling) most likely.

AT will finish after sensing the response from your system but only if the SV parameter is reached. It works this way (in simple terms :D )

Assume a heating function

SV = 100 degrees F
PV = 75 degrees F (to begin the cycle)
Press > until AT blinks (starts AT function)
The "OUT" light should be in which will signal the SSR to be on completing the circuit for the heater (turns your heat element on)
The temp PV should start to increase as heater is on
The AT function is sensing the rate of temp increase (how fast)
When PV reaches the SV (100 degrees) the OUT light should go out (actually PV will be slightly higher)
AT is then sensing how quickly the temp drops so that it can calculate the rate of heat needed to maintain the SV (100)
Then the OUT light comes on when PV is below SV (your system is "calling" for heat) and the AT is again sensing the rate of temp increase
When PV reaches SV (again maybe a degree or two above) the OUT light goes off.
If your system is reasonably stable (you do not add any hot or cold material) then the temp rise and fall should be fairly consistent and the AT will be sensing the heat up and cool down cycle.
The AT light should then go out after a few cycles of this heat on/heat off cycle and you will then notice that the OUT light will "pulse" rather than stay on constantly. This means your controller is working and the AT function is turning the heat on and off gradually.

So the AT function is looking at the ramp up (for heating) time (how long it takes for your heater to bring up the temp) and then will cycle the heater on and off so that the temp does not overshoot the SV (or undershoot).

Hope that makes sense!

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Re: How long does Auto Tune take?

Postby Tech_Marco » Mon Jan 03, 2011 2:56 pm

Excellence post! Two tumbs up for glassguy213

Regarding to this matter, I talked to the manfuacturer last night and confirmed that glassguy213
is absolutely right. In order for the Auto Tune to work properly, the PID must connect to a heater (or cooler) and a SSR (I mean a complete system that other people called "Closed Loop System") in order to peform the self tuning. I wish I know it earlier and save customer a lot of trouble. Too bad that I'm not an expert on everything. I have to sample and tested about 300 items and keep finding new products to support the business. With you folks help like glassguy213, please accept my gratitude for your help.

Happy New Year to all and wish you all the BEST ***


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Re: How long does Auto Tune take?

Postby richiem » Mon Jan 03, 2011 11:14 pm

Situations can be really different, so caution is needed and expectations need to be realistic. For example, my new 612 is running the heater for a hot tub. This is a very slow response system, so it will take the AT function a loooong time to reach stable operation. The heater can increase the water temp about 2.5 degrees F per hour, and the heat loss is even slower, so depending on the number of iterations the AT function needs, it could be quite a while, with lots of errata, before the system settles.

It would be best to let it do it, but I don't have the patience -- so I twiddled the PID settings in ways that seemed reasonable and which have previously given good results. You can see my settings on my web page (scroll down to near the bottom of the page):

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Re: How long does Auto Tune take?

Postby glassguy213 » Wed Jan 05, 2011 6:02 am

Richiem you make a good point. But you know how your system behaves so you can understand that AT would require more time due to slow rate of change. My suggestion to you though is to turn your heaters on and get up to the desired temp. and then turn on your PID and run AT. The tuning would still take several hours based on your temp increase/decrease rates. AT does not really need to take a reading on cold start as that will be constant on for the output. AT only regulates to prevent under or over shooting of SV temp.

So the point on the length of time is this- it is a function of how quickly your system adds or loses heat. If you system is stable the AT seems to look at 2-3 cycles of up to temp, off, below temp, on, reach temp, off, below temp, on then the light will stop blinking and AT is complete. If the temp never actually changes the light will blink forever! I set up my PID in test mode with only the thermocouple and ambient air temp. So there was no change in the actual temp (PV) happening. I did AT and it will just blink forever because there is no actual change in the PV. If you want to play with the AT function and see how it works try my manual test method described in earlier post.

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