Gaggia Classic, Schematic diagrams, PID-ing

[GeorgeW]

<Can you tell me how the thermocouple is attached to the side of the boiler? I might try soldering it but access is very tight down there. The other thing I was going to attempt was resusing the threaded hole that the existing thermostat is screwed into, but it is not in the same location as you suggest. I think there is some sort of tape that can be used, but I've no idea where to get it from. >


You can buy special high temp. tape from Maplins or some other electronic retailer and can use this to stick the thermo-couple on to the boiler wall. Better use some heat transfer paste as well. I would suggest sticking this half-way down the boiler as this seems to work ok with the Silvia. Good luck.

[ben_edwards]

OK... I'm sort of up and running with the PID. I have issues though First off the manual I have is here:

http://rchobby.282.hk/XMT7100.doc

I have used the auto-tune function and the fuzzy-logic mode. The value rd is set to heating (as opposed to cooling (??) specified in the manual example - this did not work).

The issue I have is that it seems to take ages to get to temperature, and the last couple of degrees it just wont go through or if it overshoots it will settle at 2deg F above the target!?. I can tweak some of the values but I have no idea what they do Any ideas??


This is the auto tune result (no water through group):
Proportional Band: 3.9% (default 5%)
Integration time: 101 sec (default 100)
Differentiation Time: 25s (default 20)
Integration Range: 3 deg F (default 40)
On/off control Range: 109 degF (default 40)
Control Perion: 2 sec (default 2)
Digital Filtering: off (default off)

Thanks!

[GeorgeW]

Ben...have a look at Simon's article on the home page re fitting a PID and also my thread on PIDing a Silvia where Simon made some suggestions re the tuning. You can also PM SimonP and I'm sure he'd be glad to help.
I've already modified my machine but the PID was u/s and I've been waiting since June the 12th for another from ebay.

[Captain_Crema]

Ben,

I'm using the standard mode, not the fuzzy logic mode, with auto tune settings. It's very good at keeping a constant setting (97 degrees C in my case), although I do find it a good idea to hurry it along a bit by turning the steam switch on until it reaches 90 when it is heating from cold. Mind you, that's just me being impatient - it always gets there in the end (and not much slower than 6 minutes which is supposed to be the warm up time anyway). It's probably best not to mess with the values unless you understand the algorithm and underlying theory (which I don't!). I think the fuzzy mode is not intended for applications like coffee machines where most of the variables are reasonably static.

So try the default mode with the auto tune. Oh, and remember that at default it displays degrees C and the default set point is 80- or 90 (not sure which). Also, calibrate your thermocouple (set the temperature adjustment) as I described previously.

Cheers

JonB

[ben_edwards]

I've tried the normal PID mode and there is no discernable difference. As the PID is only set to the nearest degree I figure that the farenheit scale offers more fine adjustment. Although the variation (e.g. during pull) seems to remove ths advantage.Good tip about the steam switch. I have left it for a wile and it is hitting a constant 199F against 200F setpoint. During pull the temp intially goes up by 3-4F then drops quickly (185 -190 min) when you end the pull. I think this is due to positioning the thermocouple at the bottom of the boiler (old thermostat position)... so the hotter water at the top of the boiler is pulled lower just as you start the pump.

I've read that people set the pid at 220F for a cup temp of 200F - does the water really loose 20F (~10C) from the boiler to the group? Bear in mind the pid is keeping a constant boiler presure so the water temp at least at the height of the tc will be constant and equal to that of the boiler.

I think I need to read up on the algorithms used in the pid.. I am really confued why it levels out at different teperatures and doesn't adjust to the target? Earlier on I was getting 197F... then at one point 193 and most of this evebing (longest up time) t was hitting 199. I'm happy eith the 199F but will have to test more re the variation. Maybe it is the fuzzy logic learning to cope with the temperature gain when switchng the brew on?

t seems at the moment that the longer leave it the more stable it is becoming which makes sense.

[ben_edwards]

I've wired my PID nto the classics supply by the way. I couldn't find any info on this so poked around with a properly setup multimeter and found that the bottom (nearest the drip tray) two wires on the on/off switch (the middle has two blue* wires the bottom has one black* wire going into the swich) provide 240Vac whe nthe switch s on. So connectng across these wires will power the PID. ( I have no few enough plugs in my kitchen as it is!). The SSRs load is just connected to the brew thermostats removed connections.

nb colours may vary!

[CakeBoy]

<Can you tell me how the thermocouple is attached to the side of the boiler? I might try soldering it but access is very tight down there. The other thing I was going to attempt was resusing the threaded hole that the existing thermostat is screwed into, but it is not in the same location as you suggest. I think there is some sort of tape that can be used, but I've no idea where to get it from. >


You can buy special high temp. tape from Maplins or some other electronic retailer and can use this to stick the thermo-couple on to the boiler wall. Better use some heat transfer paste as well. I would suggest sticking this half-way down the boiler as this seems to work ok with the Silvia. Good luck.

George, a couple of the largest size jubilee clips that the local Homebase/B&Q stock joined head to tail making one large one around the boiler did the trick (Simon's idea). It's worth putting some padding between the clip and t/c head to prevent damage and false readings. A bit of your excellent sticky padding with a covering of electricians' tape then the jubilee clip worked well. Shout if this is all waffle and I'll try again in clearer language

[GeorgeW]

<Can you tell me how the thermocouple is attached to the side of the boiler? I might try soldering it but access is very tight down there. The other thing I was going to attempt was resusing the threaded hole that the existing thermostat is screwed into, but it is not in the same location as you suggest. I think there is some sort of tape that can be used, but I've no idea where to get it from. >


You can buy special high temp. tape from Maplins or some other electronic retailer and can use this to stick the thermo-couple on to the boiler wall. Better use some heat transfer paste as well. I would suggest sticking this half-way down the boiler as this seems to work ok with the Silvia. Good luck.

George, a couple of the largest size jubilee clips that the local Homebase/B&Q stock joined head to tail making one large one around the boiler did the trick (Simon's idea). It's worth putting some padding between the clip and t/c head to prevent damage and false readings. A bit of your excellent sticky padding with a covering of electricians' tape then the jubilee clip worked well. Shout if this is all waffle and I'll try again in clearer language

I can't see anything wrong with the jubilee clip idea really..I would imagine it would be fine. Have you any info re the temp stability you have had from your mod yet Cakey?
I've emailed my supplier but no word as yet.

[ben_edwards]

The other thing I was going to attempt was resusing the threaded hole that the existing thermostat is screwed into

I have removed the end of the thermocouple as you suggested revealing the small metal sphere at the end. I then removed the boiler by removing the allen type screws around the grouphead. Then I removed the steam wand from the boiler. The boiler can then be lifted somewhat clear of the casing (the wires prevent too much movement). Now the brew thermostat can easily be accessed. I removed the thermostat and found a screw which would fit in its place. I soldered the ball bit on the end of the thermocouple into the cross of the screw and screwed it into the hole by hand.

In this position the pattern of temperature change during a pull is to increase during infusion+a few seconds from the initial 199F to 201F (hotter water forced down from top of boiler), then the temperature drops as the cold water from the tank enters the boiler and mixes. I think it may be beyond the capabilities of the PID to have an aggressive heating routine during the pull (but please correct if I'm mistaken) as it cannot differentaite between static boiler water (which auto tune is testing) and water flowing into the boiler.

Anyway, as noted by many the usual thermostat range is huge. FOr the majority of the pull the PID keeps the temp to +/-5F or +/-2C which is great. I have noticed that the usual layering (different tastes at different levels in the cup) of my espresso has vanished. I look forward to recreating all those seperate flavours in individual cups!

[GeorgeW]

Ben Said<I think it may be beyond the capabilities of the PID to have an aggressive heating routine during the pull (but please correct if I'm mistaken) as it cannot differentaite between static boiler water (which auto tune is testing) and water flowing into the boiler.>

From what I've heard this is correct Ben. The PID plays no part in this part of the cycle.

[ben_edwards]

So... now I just need to insulate me boiler and add a pre-heating element to the inflow!

[ben_edwards]

Just tried bumping it up to 208F (99C) from my previous 200F (93C) and the comparison is akin to wine and dishwater! The 208F brew is weak, thin and sour/bitter, crema is thin settling at a few mm. The 200F brew was thick, and well balanced with a thick crema. These settings will obviously be applicable to my thermocouple location only.

[CakeBoy]

I can't see anything wrong with the jubilee clip idea really..I would imagine it would be fine. Have you any info re the temp stability you have had from your mod yet Cakey?
I've emailed my supplier but no word as yet.

The jubilee clip thing is fine with the end screw of the proble removed as Ben describes. Plenty of padding keeps it safe and prevents erroneous readings.

It is stable but tends to overshoot. So far thoughts are:

1. It is great to be able to start a shot from a specific temperature point.
2. Recovery back to that point is relatively quick.
3. There is the temperature loss during the shot as the machine begins to cycle. There is nothing that can be done here due to the boiler size.
4. It is very hard to programme a PID to reduce overshoot.
5. I don't think this one has fuzzy logic which would have helped with point four.
6. There are better PIDs on the market.
7. SimonP would be able to get it working better.
8. I still don't like the taste of the espresso from Audrey compared with L'Anna.
9. A good value for money addition to avoid temperature surfing and allow specific start temps for various beans.

I'm waiting for you to find a decent enclosure George, and I will copy you as always

Don't forget to let me know how your delivery issues pan out and remember I have the correct manual here too.

[Captain_Crema]

Eh? Is your PID the one from palmelectronics then, CakeBoy? According to my manual, it has the fuzzy logic mode. And I haven't noticed any of the problems that ben is experiencing (although my thermocouple's on the top of the boiler, clamped there by the earth tag).

[ben_edwards]

Cakeboy I used this enclosure from maplin, nice brushed steel finish on them to take your eye off my awful attempt at cutting the bugger!

http://www.maplin.co.uk/Module.aspx?Mod ... e&doy=10m8

I've switched off the fuzzy mode now as, although it keeps a good temperature, if I adjust it by a couple of deg it is taking ages to creep up or down (from rebound temps hit the mark just not fine adjustment). The standard mode gets there (stable) in a few minutes. I'm having no problems as such I just wantto mke sure I'm getting the best out of the PID. The only problems I have are ones which cannot be rectified e.g. non-linear system when brewing etc. Otherwise I get nice stable temps (slightly lower than the target - which is due to the PID theory - and may not be noticable on the C scale). C_C what are your auto - tune settings? I wonder if my integral time is slightly long at 101s, maybe lower will help maintain temp when brewing? (its set->0036 to view the PID values).