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Another PID question

PostPosted: Fri Apr 15, 2016 15:47
by Pakman
Having sorted out an air bleed valve at the top of the kettle coil I now need to understand why the PID continued applying power to the heating element after the target temperature had been reached.
Any-one out there got a typical set of settings that should be entered in the PID so I can compare please? :hat:
Graham

Re: Another PID question

PostPosted: Fri Apr 15, 2016 21:21
by Dave1970
My memory of doing mine is a bit fuzzy, but I think you have you run an autotune. Mine overshot the temp by a lot when I first ran it and the autotune sorted it. I would guess that they're set up for much bigger industrial volumes and don't expect the system to be as responsive as our relatively small volumes, the autotune 'teaches' it your system.

Re: Another PID question

PostPosted: Sat Apr 16, 2016 09:15
by mark1964
if you run the auto tune use water already heated up to around 50 degrees then recirc through the herms etc

Re: Another PID question

PostPosted: Mon Apr 18, 2016 14:17
by ockelford
Just an obvious thing, if you can work out how to start autotune, then there are couple of factors to bearing in mind:
1. The setup in terms of volumes of fluid and flow rates should match your real world scenario.
2. Due to the way a mash stops free mixing of the water in the tun, when setting the PID autotune, dump the water leaving the tun, don't recirculate into the tun, it will change the temperature of the water going into the HERMS coil faster than would recirculating wort.
3. Rrun the autotune near to typical temperatures you will mash at, say 65 deg C.
4. Don't autotune during a mash. It deliberately overshoots to see what happens in order to evaluate the characteristics of the system and works out the P.I.D values from this. You will ruin your brew, if you do it then!

Just a couple of things I learnt along the way, but you need to tune it to your system, there isn't really a 'right' setting.

R