Help! Anyone PID a Dalla Corte?

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Frosted
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Joined: 11 years ago

#1: Post by Frosted »

Does anybody here have any experience with putting a PID controller on a Dalla Corte? I am trying to figure out a good thermocouple solution and a way to by-pass the current temp adjustment pot. I want to be as prepared as I can for this project, to minimize the machine's downtime. The machine's current setup has a temp probe in the brew boiler. I am assuming it would be way to convenient for that to work with the PID. Life never seems to work that easily. So I am wondering whether a thermocouple attached to the boiler (either at a fitting or adhesive) would work well. And leave the current probe in place and just disconnect it. Or if I should try to figure out how to replace the probe with the appropriate thermocouple.

Thanks for any help you can be.
Rik

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Carneiro
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#2: Post by Carneiro »

That probe is a NTC. I'm not particularly fond of it's location, but if you want the probe inside the water, that's the one you already have!

You could use some tiny TC or PT100 touching the boiler, new the group. The inercia would be a little bigger, but it would reflect better the actual temp of the group. As far as I remember, DC temp on a Scace was around 2-3°C lower than the potentiometer reading, but we can't even know if the system they use is very well calibrated or if there is some offset.

Márcio.

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Frosted (original poster)
Posts: 6
Joined: 11 years ago

#3: Post by Frosted (original poster) »

Márcio,
Thanks for the response. I don't really care if the probe is in the water, so I'm leaning toward using a TC that attaches with an adhesive patch. I'll just leave the old probe in place. Still got to figure out the wiring work-around. Any other thoughts?
Thanks,
Rik

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Carneiro
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#4: Post by Carneiro »

Now you got me... I don't remember the electronic boxes and wiring.

Frosted (original poster)
Posts: 6
Joined: 11 years ago

#5: Post by Frosted (original poster) »

I have finally gotten to this project. I've wired the PID and used a surface mount "T" tc connected to a Fuji PXR3. The tc in attached to the lower portion of the boiler. Here is what is happening. The thick brass wall of the boiler is creating a big offset. When my extractions read around 202°F at the puck, the tc is reading around 180°F. Around 20°F+, which is beyond the max offset setting on the controller. It also, as expected, creates a pretty big lag in the temp readings. So I suspect it keeps the boiler on too long when it is responding to a shot being pulled. When auto tuned, the temp is very stable at idle, but when you pull a shot, it really over-shoots and then is quite slow to cool down. I tried adjusting the parameters one at a time and got the P function pretty good at around 4.5-5.0, but as soon as I added any amount to the I function, the boiler over shoots again. I had to set it in the mid 300s to get it to reduce at all and it was still overshooting, big time. Do I keep going up from there? As far as the D function goes I don't know that it can neutralize the overshoot. Or where to start.

Any suggestions would be greatly appreciated.

I am thinking I may need a different tc solution. Maybe a probe in the boiler. Anyone know the size of the current temp probe?

Thanks,
Rik

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Carneiro
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#6: Post by Carneiro »

4mm diameter, I think 25mm long. Just a cylinder inside a SS tube connected to the boiler. The probe they use is a NTC, but think you can make a TC or PT100 to fit there. You could even test with a wire TC and some thermal paste.

Frosted (original poster)
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#7: Post by Frosted (original poster) »

Márcio,
So I understand, is the NTC a tube (probe) in a SS tube? If so, can the probe be pulled out or is it attached to the SS sleeve and they must be removed together with a wrench?
Thanks,
Rik

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Carneiro
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#8: Post by Carneiro »

You can just remove the SS probe from the sleeve, there is nothing holding it.

Frosted (original poster)
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Joined: 11 years ago

#9: Post by Frosted (original poster) »

Márcio,
Thanks so much for your help with this. One clarification. The probe does not touch water? It is enclosed in the sleeve? My intention is to make a probe with the thermocouple wire I already have and 4mm brass tubing. If it does not have to be water tight, I can construct it differently than if it does. I am not finding anyplace that sells a probe style thermocouple to the appropriate specs. With the thermocouple in its current position reading the outside of the boiler, the overshoot is way too great and I have been having great difficulty tuning the PID to eliminate it.

Rik

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Carneiro
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#10: Post by Carneiro »

I let it way above the water, were the steam rules...

Try the Omega website, they have a extensive catalog.

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