# PID keeps overshooting?



## cavem01 (Oct 3, 2015)

Hi guys my PID keeps overshooting..... any ideas why??


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## DaveP (Jul 14, 2017)

Possibly .... the 'heat sensor' is slow to respond to temperature changes, either due to poor physical contact with the boiler or it has a poor electrical response.

So that's what I'd check first.

Then 2nd maybe its forgotten its training / tuning ... but a tiny bit of overshoot maybe inevitable


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## timmyjj21 (May 10, 2015)

My Gaggia PID always overshoots on initial heat up. I assume it's down to training, but don't really care since it stabilises well once warm.


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## mcrmfc (Sep 17, 2016)

Check that the thermocouple or pt100 sensor hasn't moved or come out of place. If it has or if any other aspect of your machine could have changed its thermodynamic properties e.g. new dispersion plate then check everything is located securely and re run the auto tune.

Overshooting is fine in the early heating up stage but the autotune learns about the heating cycle and can set the algorithm params appropriately to minimise that swing.


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## ZappyAd (Jul 19, 2017)

I'm interested to find out more about the algorithm that makes a PID work. Is there a good resource or thread for finding out more about it?


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## mcrmfc (Sep 17, 2016)

ZappyAd said:


> I'm interested to find out more about the algorithm that makes a PID work. Is there a good resource or thread for finding out more about it?


https://en.m.wikipedia.org/wiki/PID_controller


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## cavem01 (Oct 3, 2015)

mcrmfc said:


> Check that the thermocouple or pt100 sensor hasn't moved or come out of place. If it has or if any other aspect of your machine could have changed its thermodynamic properties e.g. new dispersion plate then check everything is located securely and re run the auto tune.
> 
> Overshooting is fine in the early heating up stage but the autotune learns about the heating cycle and can set the algorithm params appropriately to minimise that swing.


Thanks for that. I've never ran the auto tune was always told not to! To do this do I get it up to temperature and run the auto tune? Aka let the machine warm up?

Mike


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## martinierius (Sep 28, 2014)

cavem01 said:


> Thanks for that. I've never ran the auto tune was always told not to! To do this do I get it up to temperature and run the auto tune? Aka let the machine warm up?
> 
> Mike


Indeed, also: some people advise to run the autotune with the desired temperature a few degrees lower to avoid overshooting to boiling temperature.

When boiling you get steam in your boiler which then affects the autotune parameters.

After tuning you set the desired temperature again to original setting.

Before 'autotuning' it's best tot purge the steam that might be in the boiler.


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