# What does PID stand for?



## Dash (Feb 6, 2020)

Stupid question here - what does PID stand for? I've read a few posts about people wanting to "PID" Gaggia Classics... can someone explain what it is and what it does to the machine?

Thanks!


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## MediumRoastSteam (Jul 7, 2015)

Dash said:


> Stupid question here - what does PID stand for? I've read a few posts about people wanting to "PID" Gaggia Classics... can someone explain what it is and what it does to the machine?
> 
> Thanks!


Let me google that for you...

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

The short read is that, it can be used to keep the temperature of the water inside the boiler at a much more stable and optional for brewing or steaming, instead of simply having a thermostat with a wide dead band and therefore longer recovery times or unwanted temperatures.


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## MildredM (Feb 13, 2017)

Dash said:


> Stupid question here - what does PID stand for? I've read a few posts about people wanting to "PID" Gaggia Classics... can someone explain what it is and what it does to the machine?
> 
> Thanks!


 Not many would know what it stands for (we would be more likely to know what it does)

PID = *proportional-integral-derivative *


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## L&R (Mar 8, 2018)

In coffee world this is stable temperature while extracting espresso hence consistent taste in the cup.


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## Dash (Feb 6, 2020)

Thanks all! Very helpful.


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## Cooffe (Mar 7, 2019)

A PID is a device that maintains temperature (or any other variable) via means of signalling. Generally a PID is much more temperature stable due to there not being a switch constantly switching a thermostat. Below is a graph of a thermostat (blue line) Vs a PID (red line). You can see how a PID doesn't rely on a thermostat switching and hence no large fluctuations.

We use them a lot in electrical motors mainly for torque control as you don't have a massive overshoot at the beginning which can damage intrinsic components. In espresso machines they're being used maintain temperature stability within +/- 0.1ish degrees as opposed to having to temperature surf (generally a 10 degree deadband or so) the last version caravel is a good example, and a Gaggia classic.


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## Deidre (Aug 13, 2019)

@Cooffe I think your kind & generous approach here is just what the original poster was looking for, hoping to get a clearer understanding of a foreign concept! Well done you! ?☺


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## MrShades (Jul 29, 2009)

... and if you really want to know - then PID refers to the three main parameters that are set as part of the algorithm that calculates how much 'power' (or for what percentage of time full power is applied) in order to make the PV (process variable - ie the current temperature) closer to the SV (set point variable - ie what you have the temp set to).

P = proportional

I = integral

D = derivative

It's all scary complicated maths - but in essence the P controls the power based on how far away from the SV the PV is, the I helps to correct this further based on accumulated error (anyone who understands integrals in mathematics will have more of an idea) and the D can improve the ability to settle at the SV.

As others have said - it's the best way to control heating elements in an espresso machine, to give as stable a temperature as possible (given the physical constraints of the rest of the espresso machine design)

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## Cooffe (Mar 7, 2019)

MrShades said:


> ... and if you really want to know - then PID refers to the three main parameters that are set as part of the algorithm that calculates how much 'power' (or for what percentage of time full power is applied) in order to make the PV (process variable - ie the current temperature) closer to the SV (set point variable - ie what you have the temp set to).
> 
> P = proportional
> 
> ...


 Oh god you're bringing me back into mechatronics and industrial process control... Please don't make me relive simulink and MATLAB ?

When should we mention that you can get just PI and P controllers and that they're only really as good as the sensor used... Pt100 anyone?


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## ajohn (Sep 23, 2017)

D is effectively the rate of change. Differential in other words, slope of the current change in temperature etc

I is an integral - an area of the error over a period is one way of looking at it.

P is proportional also some times called part but not often. That is the difference between actual temperature and the set temperature.

Maintain the temperature exactly during an extraction - depends on several things.

Hit an "exact" temperature when a boiler is heating and keep it there - yes. The general idea is that the heating element is at the same temperature as the water when it gets to the one that has been set. That way further heating stops when the heating is turned fully off. That aspect is what can make maintaining a set temperature when a shot is pulled difficult.

John

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## Fairkid (Feb 9, 2020)

Thanks for good info as I was wondering this too.


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## MrShades (Jul 29, 2009)

Cooffe said:


> Oh god you're bringing me back into mechatronics and industrial process control... Please don't make me relive simulink and MATLAB
> When should we mention that you can get just PI and P controllers and that they're only really as good as the sensor used... Pt100 anyone?


In case anyone is wondering :

Pt - it's made of platinum
100 - which has a resistance of exactly 100ohms at 0c

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## ajohn (Sep 23, 2017)

The proportional parts is easiest to understand. It too can leave the heater temperature the same as the water when it's turned off.

Say some boiler turns out to be able to take some heating energy of 1000 units and a constant of 0.5 was used. This will get the water temperature to some point. The next step would be 500 units. That would lead to another temperature so 250 units would be used and so on, next one would be 125

The 1000 might be the power of the heating element. The temperature of the water is checked and a sum done to set the power to the heater. I used stupid numbers, no steps, it's done continuously but clearly temperature will take some time to get there. The P in PID used on it's own would usually overshoot as this gif shows . It then adds the integral, more overshoot and then the differential terms. Notice it isn't exact. At some level few things are.









There are variations on how it's done. The numbers just go into a sum that is used to set the power of the heater and the sum is done often enough to make things look like they are continuous. It has very probably been done with op amps in the past. Lots of control loops have.

John

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## PortaPaul (Nov 3, 2019)

Mr Shades Proportional Intigral Derivative kit is great!


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