PID

[kingseven]

OK - I like to think I know at least a little about espresso.

But I know very little about technical stuff. Would someone be very kind and explain to me what PID is all about?

I'd be terribly grateful.

[HughF]

In this context PID means an electronic feedback circuit (you need temp sensor, feedback circuit, relay to switch heater, display and control buttons) used to achieve precise and constant temperatures; it replaces a conventional thermostat/pressurestat. It's mainly used for controlling brew water temperatures in espresso machines. The Reneka Techno does something similar out of the box, almost all other machines need to be modified. You can choose a temp (to suit the specific beans and their degree of roast) within 0.1 degrees and the circuit will tell you when that is achieved, then you pull the shot. People with Rancilio Silvias have used the Fuji PXR3 box IIRC.

It costs maybe £150-£200 all in so you would probably buy a decent espresso machine (at least something with a 3-way, maybe an HX also) before adding a PID circuit. For example, a Silvia with a PID would make better espresso than a stock Silvia but you would still have to wait just as long to steam after brewing.

Randy G's site at :
http://www.quiknet.com/~frcn/Coffee/Coffee63.html
has much better information (PIDing Silvia) and several useful links. If you haven't seen his site, I strongly recommend it.

Cheers,

Hugh

[kingseven]

I assume this technology can be applied to a commercial machine?

*Cracks open the side of the Gaggia GD 2 group*

[HughF]

Sure. Try Searching for Barry Jarrett's posts on alt.coffee using Google Groups. He's PIDing an LM at home and there are pictures of some of the rebuild on his Web - site see the bottom of the page to find the bit about the PID :
http://www.mindspring.com/~coffe/lm2grp2.htm

Cheers,

Hugh

[kingseven]

Hmmm..... I wonder if I can convince the engineers at head office that they need to dig one of the machines from the graveyard and do this to it. Then give it me. For free.

May be a tall order.....

Thanks for the links Hugh, should help speed today up!

[simonp]

I'm in the process of doing an article on the PID fitting on my Silvia. I did mine for peanuts. I got a PID controller (not the Fuji PXR3, but works fine) on ebay for £7.50, I had to buy a transformer & thermoucouple but the total was around £20.
For the record, PID stands for Proportional Integral Differential, which describes the 3 calculation methods it uses to control the temperature.
PIDs are not really designed for use with the system with a thermal mass as low as a small espresso machine, but seem to cope quite well. I susspect in a commercial machine one would work even better.

[phil]

See my comments on Paul's thread.

I think Barry may be successful because LM's are dual boiler, no? So you've got thermostats rather than p-stats. Do I need to explain so people can tell me I'm talking blx?

[kingseven]

I would love to know more

[phil]

OK I'll try. This is off the top of my head so I may get something a bit wrong but as I say I'm sure lots of folk will jump in to correct me.

Right - basically we have two types of espresso machine: those that heat the brew water directly, and those that heat the brew water via a heat exchanger.

The "direct heating" machines seem to fall into two categories. In one category, we have relatively inexpensive but respectable machines like Silvia. In the other category we have "mutts nuts" dual boiler machines like the Techno which Robbie's just bought, the La Spaziale S1 and the big La Marzoccos. Here I must confess I don't know much about LM's but I do think I recall reading about them having dual boilers - maybe that's just some models? I dunno.

The "heat exchanger" machines comprise the vast majority of the espresso machine marketplace. Here hot water or steam from the boiler is used to heat a fresh water feed (i.e. not drawn from the boiler). This feed is used for brewing.

(At his point I feel like pointing out - for no better reason than mischief - that my own Gaggia TD commercial machine is a bit of a hybrid. It's basically a heat exchanger machine, but it also has an electrical heater embedded in the group head. Weird but effective in my experience).

OK - so to adjust the brew temperature in a "directly heated" machine like Silvia or a dual boiler jobby you adjust the thermostat. The circuit doing this can be made much more effective by using a PID (not wanting to steal Simon's thunder so that's all I'll say).

To adjust the temperature in an HX machine you adjust the boiler pressure, which is a very crude proxy for adjusting the temperature. So I'm simply going to say that setting up a tight and effective temperature control mechanism using control over the pressure stat is not really workable.

Makes you wonder why all machines aren't dual boiler though doesn't it? Now you can see why people are prepared to pay a premium for machines like the Techno and the S1.

Does this help?

[kingseven]

The pressure bit does indeed now make sense.

Both types of machines need temp surfing though. You have to be careful with the Gaggia if things are slow as heating at the brew head can build a bit of steam. Duals need to be temp surfed for the oppposite reason - to keep brew head temp high right?

I remember being talked through the inside of a Spaziale by the UK boss bloke - very interesting.

[pault]

so to clarify ...

it's not worth PIDing my Giotto or does anyone have positive experiences ...?

all the best,

Paul.

[phil]

I'd say not, Paul.

[Danny]

Phil, You explained it exactly the way I understand it. I think you are right on the money. Interesting about the Gaggia, maybe that's why Floz raves about his old one to me all the time.

Kingseven, You temp surf a singel boiler machine to get the water temp right *and* to make the steam last longer I think. You dont really temp surf a HX, rather draw water off it till the head cools down enough. The head in a HX gets hot beacuse most HX's have a thermosyphon system to circulate water from the boiler to the group head when idle. Eventually (after 15 minutes it's noticable) the grouphead temp approaches the temp of the boiler itself. So you draw off fresh water until the head is the right temp for a shot.

There is much experimentation here The higher the pressure in the boiler, the faster the HX will heat up at idle. The lower the pressure, the worse the recovery time, and the les steam pressure available.

Interestingly enough, there are other mods for HX's to try and mitigate the effects of the thermosyphon whilst still keeping it's advantages. Most of these are releated to insulating the boiler and the HX piping so that the HX piping does not heat up so fast.

Pault, if you have a dual boiler Giotto, then PIDding it will not do much for you as Phil said. Buying yourself an accurate temp sensor and fitting it to a filter basket to profile your heating will help you to make better tasting espresso, but may make you look strange to anyone around. (My wife thinks I am nuts). Fiddleing with the PStat may tune the machine to a point where it works best for you.

Finally,... HX's work best when the pressure is high AND they are running all day long. Leave a commercial (not a machine with a dedicated brew boiler) idle for a while and it too will overheat such that you must run some water off to cool it down. At least that is my understanding, I've never played with a real commercial machine. Still looking for a good-dead-one.

[kingseven]

Isn't temp surfing just drawing water through a group head to achieve a prefered temperature? Do please educate me on the language - I find this all fascinating.

[Danny]

I am going to talk about single boiler machines here.

Temp surfing can be a few things but basically it's a procedure that enables you to start pulling the shot, or start the steam at a given time in the power cycle of the boiler AND at a given temp for the system as a whole.

So the machine at normal temperature (warm) turns the heater on at a low temp, and off again at a high temp. This is the machine cycle. If you, for example, start to pull water through the machine immediatly after the light comes on, the new (colder) water comming into the boiler will probably cause the heater to stay on for a longer time. Adjusting when you start the shot (or indeed pulling a few blanks first) is what temp surfing is all about. Basically you are juggling the heat of the machine and the time that the power cycle starts to give you a great shot.


I have never tried this since, it's pretty useless on a HX. I just have to run off enough water to cool the head down before each shot. Some new owners of a HX find this annoying, as did I. Now I find it a challenge to get the best out of my machine. (Sarcasm on) Imagine how boring it would be if you just had to push a button for your coffee in the morning. Where's the fun in that?? (/Sarcasm off)....