PID and Thermocouple help

[hoppyscotty]

Hi. Need some help about thermocouples and PID controllers. I've been building a control panel for a 3 vessel system I got off eBay. All fired up fine and operated as intended but when testing was having an issue with it with the heating element not coming on despite having 240v supplied to them.

The thermocouples came with the setup. I decided not to use the method of control from the previous owner so embraced on building the PID control panel. Firstly I got the orAL message which I believe means the PID cant talk to the thermocouple or make sense of the signal. I assumed its a K-Type thermocouple but have tried different options in the setup to see if I get one that works.

I've measures the resistance of one of the thermocouples and it read 15k Ohms which sounds a bit high - I believe the resistance of a K-=Type should be in the low single figure of ohms e.g. 5 ohms? so maybe the Thermocouples are knackered and need replacing?

The wiring is a bit suspect too as the previous owner used Cat 5 cable so utilises pin 1 and 8 of a cat 5 plug for positive and negative, so again the problem might light with these connections?

I am just thinking about being new Thermocouples then I'll know there is no issue with them. If I do that I'll just ditch the cat 5 connections and wire directly into the PID's.

Any suggestion? Something in the setup up I need to do as I just used all the default settings.

Thanks.

 

[aamcle]

1'st get rid of the thermocouples they are too hard to calibrate. PT100 are much better and easy to calibrate.

There are diagrams either here or on Jim''s that will show you how to set it up.

 

[hoppyscotty]

The calibration seems to be done via the Inkbird PID so I assume I'd need to go through that process whatever thermocouple/sensor I'd use?

But yes, think I'll just replace the thermocouples/sensors. They're not that expensive.

 

[hoppyscotty]

Sussed it. Though I did find some minor wiring errors and I think I'll go ahead and replace the Thermocouples anyway it seems I've purchased the incorrect PID units for the job. I purchased ones with a relay output instead of an SSR output so though the unit is demanding heat its not energising the SSR.

 

[hoppyscotty]

Finally got all the parts together and its happily boiling some water while I'm doing a boil off test so thanks for the advice above. I've noticed that the boil kind of pulses, so it will boil reasonably vigorously for a few seconds then the PID will throttle back and the boil will settle down for a few seconds to a more gentle boil before the heating elements throttle up again. The measured temp never dips below 100 degrees so its maintaining the temperature. How would I fine tune this with the PID parameters? The instructions telly you how to change the various parameters but don't really explain what each of the parameters are so I'm not sure which parameters to change to fine tune and get a nice consistent boil.

Thanks.

 

[RoomWithABrew]

On my SmartPID and I believe on other setups the PID is not used for the boil.
The power supplied to the element is controlled, so once my target temp is reached ( boiling) then I dial the percentage back to about 30%. I'm sure I saw this on the American forum maybe electric brewing brucontrol thread.

 

[hoppyscotty]

I'd come across this too but after watching many videos about home built control systems PID's seem to be widely and commonly used as well as in commercial controllers. I did look for a suitable voltage regulator but cannot find one that can deliver the continuous rating for my heating element so not a viable option anyway it seems. Despite this the PID seemed to do a fine job in maintaining the boil in testing so far but just needs some fine tuning. I think I'll just try messing with the settings to get a feel for their impact.

 

[RoomWithABrew]

I don't know how the power is adjusted on the SmartPID but it's a very small box and a 40A SSR which can control the 3500 watt element. There are small relays inside the box for pump control only.

 

[hoppyscotty]

I actually have a SmartPID that came with the stuff I bought but have not used that and keeping aside for a Brewzilla mod project. With PID the power is regulated by very quickly turning on and off the supply to the element so that over time the average power is lower than the rated power. The downside to PID controlling the boil I've come across is that they produce quite a vigorous boil but that wasn't my experience in testing so far with water, a gentle rolling boil was maintained but it sort of pulsed...so boiled then settled down to a simmer, then after a few seconds builds back up to a full boil, so I think I need to change the PID control settings to maintain a more consistent boil just not sure how the settings in the PID will affect the boil.

There is a manual setting in the PID controllers...not sure how that works but maybe that can be utilised too.