peacecup wrote: You will still need to work out the boiler temp:brew temp relationship...
PC

I may have missed something but I believe the 2 channel controller Jim is describing considers both TC readings simultaneously in determining the amount of power to apply to the element. Jim is this the case? Or is the second TC channel just reading the temp at the group?

I have recently acquired a Sama Export and was considering adding a PID so i'll be following along with interest.

PM sent.

Jim

sorrentinacoffee wrote:Exactly Peacecup- actually I have found that the Sama (Elektra) and PV groups seem to cool themselves reasonably quickly.Having a direct LED readout from the neck of the group will make taking that flying f!@# just that bit easier... . Will be immediately possible to see exactly how the group warms up as the thermosyphon kicks in- during and after shots- flushing, and with changes to the boiler pressure/temp from the PID.

With regard to the group head temperature, don't you think measuring the neck temperature or the housing temperature is sort of off track - i.e. too far removed from where the actual extraction is taking place? What I'm more interested in is the actual temperature within the group head (when the water makes contact with the coffee itself).

Why not install the 2nd temperature sensor in the bottom of the basket (like what I'm considering on my machine), so the probe will measure exactly the temperature that the coffee is experiencing? Then just have a stand alone PID controller (or something) to monitor the temperature. It seems to me that having the 2nd sensor in the neck of the machine won't really give you a true reading on what is going on inside the group head (and thus the exact temperature the coffee is seeing). Even if the neck probe is making contact with the water just before it enters the group head, I still don't think you are going to be seeing the same temperature where the water mixes with the coffee in the basket.

Also, having the 2nd probe in the basket (instead of attached to the machine), will allows you to keep the overall installation cleaner as far as the machine itself is concerned.

Just a thought

Ray

Ray- I have thought about that- however having a probe mounted to the pf- or basket- would be very inelegant. The good thing about the neck of the group is that is the point where the thermosyphon connection warms the group- and there is already a hole for the probe in the perfect spot. It will be nice and clean_ the probe wire will emerge from the face of the machine just under the group and bolt in at the underside of the group... all things going to plan.

The probe would not read the temperature at the coffee- but I think it would be close when the machine is at full operating temp- likely a few degrees lower? I thought it may be possible to extrapolate the difference (possibly by doing some tests with another probe in the puck) and to then calibrate the group probe accordingly. It may be that the temp is all over the place- and won't tell me much of use- but it will still be fun to watch! As soon as water is drawn into the group the neck heats up rapidly. After a shot the temp declines and stabilises. Being able to accurately read the temp at the group when the machine is turned on but not being used- and being able to control the boiler pressure easily- may allow me to determine to optimum setting for the boiler pressure in relation to the operating temperature of the group head vis a vis the thermosyphon loop ...

Even better would be to drill a hole right into the back of the piston- with the tip just inside the cylinder. This would show the changing temp throughout the shot as the group draws heat from the water. I imagine the tip would have to be perfectly flush with the piston wall though (it may work if it was inset a little- but would probably cause leaks as the piston seals pass over the hole)- and I would never attempt such a difficult mod.

Unlike you: I don't see myself lowering the pressure of my boiler much- the difference between the Pavoni and the Sama is the heatsink abilities of the group. Even though the water in the boiler is near boiling- the group can consistently draw out and dissipate the excess heat before the water reaches the coffee. The Pavoni at normal operating pressure can only achieve this feat once- before the group overheats. You need to let the entire machine cool before you can go again.

I have never quite understood how the Sama and the PV thermosyphon group attachments do their trick: I understand how the thermosyphon operates to pre-warm the groups- the boiler water can circulate in the neck- but I am not so sure how (or if) the loop draws heat from the group after a shot. I would have guessed even after a shot the group would still be cooler than in the boiler... But it seems that it does? I am not sure if this is due to the loop- and/or the group designs (large amount of brass- bolted to a frame which is removed from the boiler= rapid heat sink and dissipation= group cool for second shot)...

Jim,

you set up looks perfect- much smaller than a standard boxed PID- thanks for posting those quality photos. It looks like I could mount most of it in the base under the boiler (which should be a cool and dry spot for the electronics)- with only the display mounted in the main cabinet beside the boiler...

With you LCD (?) display- does it have a faceplate- or would you drill separate holes for the four buttons? Would it be possible with your set up to use a different type of display? Like LED? I already have a hole in the face where the on/off rocker switch was- that hole is 35mm high by 20mm wide- I can safely enlarge it to 60mm in either direction.- it would be incredible if I could somehow squeeze two micro LED temp displays into the existing hole- stacked on top of each other- boiler in green and group in red... .

I thought about drilling down through the group head piston and rod and installing a TC or RTD sensor through there. The only issue is the cross pin, although I could probably drill a very small hole in order to allow the wires to come up, yet still allow the cross pin to function. This would allow me to mount the RTD sensor in the middle of the group head piston, such that it makes perfect contact with the water being pressed down into the puck.

As far as drilling into the basket, my idea was to have a 2nd basket and only use it to dial in the temperature. Then once I have a feel for where the group head temperature is relative to the boiler (i.e. PID set temperature), then I would go back to using the normal basket.

This approach wouldn't allow me to monitor the group head temperature on every single shot, but it would be a useful diagnostic tool I think.

I'm definitely interested in seeing how your project comes along.

Ray

EDIT:

Jim I re-read you post- and your PID is actually perfect. I had spent so many hours looking at regular off the shelf pids I had become transfixed. At first I skimmed it too fast. Having re-read it I think it is the best solution for this project and I would love it if you could customise one for me. Is the fact that I am in Australia and on 220 volts a problem?

some questions:

1) I assume this can be configured to 'read' from the group- and control the ssr/element/temp from the boiler probe only?

2) The Sama machines works with a standard P-stat system- turning the element on and off. Does your PID system allow the element to be 'dimmed' effectively- using less than full output after the set temperature has been achieved? Would that require some type of transformer or something? You display shows the element at 100%- so I am just wondering- or is the the element/heat source different in your machine?

3) The timer: I assume that resets when the espresso machine is turned off? It's a nice feature...

4) If I was to house the screen assembly only in a small case- mounted to the front of the machine (rather than set in a cut-out) how wide would it be? And can you read the screen if you are looking down from above at it- does it need to be at eye level? (to be honest I am down there anyway looking at the bottom of the naked portafilter basket...)

You screen looks so small in every parameter except length- I could possibly fit it into the the base of the machine- below the drip tray. That way I could install the rocker switch as original and not have to cut a hole in the face of the machine. If you panel mount just the screen how big does the hole need to be? It would also keep the screen away from the milk frother... but under the drip tray (I could drill a small hole at the other end so if the tray ever overflowed it wouldn't leak where the screen was.

thankyou very much for the images and detailed explanation.

sorrentinacoffee wrote:With you LCD (?) display- does it have a faceplate- or would you drill separate holes for the four buttons? Would it be possible with your set up to use a different type of display? Like LED? I already have a hole in the face where the on/off rocker switch was- that hole is 35mm high by 20mm wide- I can safely enlarge it to 60mm in either direction.- it would be incredible if I could somehow squeeze two micro LED temp displays into the existing hole- stacked on top of each other- boiler in green and group in red... .

The LCD is a standard 16x2 character display (the size of the black part is around 72mm x 24mm). They are available lots of places for $12US to $15US, but I'm not aware of any pre-made faceplates. I've made acrylic (Perspex) panels with suitable cutouts for the display and buttons for some other applications, but that might not suit this project.

An small LED display would be really nice here. It would "only" be a matter of rewriting some code and designing a hardware interface But I don't have anything like that available.

Jim

PS - have you looked at the Faustino system? It looks like there is a faceplate included.

sorrentinacoffee wrote:Is the fact that I am in Australia and on 220 volts a problem?

Shouldn't be. You would just have to be sure that the wall wart and SSR are OK at 220. Most of the one's I've seen would be fine. I can help you find suitable components.

sorrentinacoffee wrote:2) The Sama machines works with a standard P-stat system- turning the element on and off. Does your PID system allow the element to be 'dimmed' effectively- using less than full output after the set temperature has been achieved?

It uses pulse-width-modulation (PWM), which sends variable length pulses of "ON" time depending on how much power is called for by the PID calculation. Normally, it is set up so the element receives a pulse of somewhere between 0 and 1000 milliseconds duration. The pulses are spaced 1 second apart.

sorrentinacoffee wrote:3) The timer: I assume that resets when the espresso machine is turned off?

Correct.

sorrentinacoffee wrote:4) If I was to house the screen assembly only in a small case- mounted to the front of the machine (rather than set in a cut-out) how wide would it be? And can you read the screen if you are looking down from above at it- does it need to be at eye level? (to be honest I am down there anyway looking at the bottom of the naked portafilter basket...)

The circuit boards are a little less than 80mm wide, so the enclosure would need to be wider than that. I can give you a CAD template showing the layout of the display and buttons. I think this will be the most challenging part of the project, and the part that I can provide the least assistance.

If you are going to view it from above most of the time, then it might be a good idea to tilt the enclosure upwards.

Jim