PID offset theory

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hadriano

#1: Post by hadriano »

Hello all
I return after more year to ask something in this excellent and exceptional forum.
I don't have very clear the variable offset in PID settings ( my machine Izzo duetto 2) .
I know what is offset, but a simple question: if the environment is too low for 20C ( standard value) and I want the same 93C of water group, THE OFFSET WILL BE TO LITTLE RESPECT 10C , maybe 8C, 7C or too high? In any case the range of values in my pid is from 11 to 1, too high from ideal 10 is only one unit.
the theory is clear if environment is cold, the heat change between group and environment is high and I want boiler to be too hot to compensate the heat losing and maintain same 93C for group.
I realize after more time my machine not make water hot , the pid indication is ok,93C but coffee appears not good. I tried all, pressure, dose, ecc, I was sure about machine temperature indication, but I was wrong. Probe is free of scale but the water is 6,7 degree Celsius to cold respect what I see in PID display.I don't have Eric thermometer, I tried to measure with a simple kitchen thermometer accurate but not quickly but was sufficient to see a big difference between PID and reality. I put T1 to 102 and I make a good nice classic coffee after more time. I roast coffee from many years, I liked light rost and you believe the unpleasant accidity of light roasting and little brew temperature. I try to see where to buy the new probe. Is strange, I live in Italy,( I'm not Italian) , izzo is made in Naples, but the spare part is impossible to find in the specialized sites I ask why....is not a historical trademark....The "real good Italian trademarks" is all in North, Milano, Torino. oh my Good :)

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another_jim
Team HB

#2: Post by another_jim »

Here is a simple technique
Jim Schulman
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La Marzocco · Home: customized for espresso aficionados
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Jeff
Team HB

#3: Post by Jeff »

Before guessing about theory, here is a good way to set the PID offset for your conditions. If you aren't near sea level, use the boiling point for your altitude, not 100° C.

Edit: This is the same link Jim gave above

Getting accurate shot temperature displays on PIDed double boilers without a thermometer

With that, I don't think you need theory or expensive equipment.


Here are some guesses of mine about the theory. They may be completely wrong.

If the group surface is around 90° C and the room temperature is around 20° (68° F) then the difference is around 70°. I think the heat lost by the group is roughly proportional to that difference (unless you're in a windy room). I think that the heat flow between the boiler and the group head may be roughly proportional to the temperature difference between those two. That difference would be close to the PID offset. If it were 13° C in the room (55° F) then there would be somewhere around a 10% difference.

hadriano (original poster)

#4: Post by hadriano (original poster) »

I know more or less the all theory. Is very useful to know more about all this aspect. With my Duetto at home I not drink to often espresso at bar, but time to time happening. In Italy exist big density of bar, 80% not made good espresso. But a few ...made a good one. What I want to say is, personally, I know how will be a "good" espresso. ( here the big importance is to find a ideal miscela of 3,4 coffee variety). To conclude, I believe all persons after a few years of experience with espresso and a high level home machine FELL IMMEDIATELY THE DIFFERENCE OF FEW DEGREES, AND ADJUST PID WITHOUT SEE THE DISPLAY INDICATION. I'm upset with me to not feel and understand quickly why my coffee is not nice. My actual preoccupation is to understand and quickly interpreted the extraction and to proceed accordingly with the mind ideal coffee.
To return at the topic. I will do all experience with boiling point to see where is my PID indication related with reality. Is strange how the probe lose the accuracy, maybe is normal after 10 years but I believe is only a k probe, nothing complicate and sofisticate.

Espressoman007

#5: Post by Espressoman007 »

When you say that room temperature is 20° C, is it 20° C all year long? During winter, my room/kitchen temperature is 21/22° C, but in the summer it's 26-29° C.
If you set PID on those 20° C, if the situation is like mine, when room temperature rises you're going to set it again?
I have Bianca, and I've seen people are changing PID parameters. Even I am tempted to see if my Bianca is accurate, or close to accurate, I still didn't check that, because my espresso is great, even with that discrepancy in temperature during the year.
I can't install thermometer on Bianca, I'd like to if it was possible, and if you can do that, why don't you. You can order one from those people in Romania:
https://coffee-sensor.com/product/tempe ... ermometer/

It's not the cheapest thing in the world, but if you can invest in it then I'd suggest you do that, before anything else. I had one in my previous machine, Bezzera, and it helped a lot in timing, when to pull a shot.

Cheers!

P.S. How come there's no popular Italian coffee forum? I was searching for it, but never managed to find it.That's been bugging me for a long time... Since I loooooove Italian coffee.

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Jeff
Team HB

#6: Post by Jeff »

The probe and meter are probably good.

6-7 degree drop between in the basket and in a cup seems reasonable.

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cafeIKE
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#7: Post by cafeIKE »

An offset on a e61 PID is almost certainly wrong.
It's never linear.
Boiler temperature varies with the seasons for the same group temperature.

If you want precise temperature control, an e61 is the wrong machine - but I wouldn't trade.