# Geeky PID question



## chrisalmond (Jan 18, 2013)

Ok then my PID has arrived from China, SSR and thermocouple included, so now ready to get modding. Before I begin though I want to know a couple of things and thought one of you on here may help me?

Firstly the thermocouple itself, when I unscrew the old thermostat will I get water gushing out of the boiler, or does it only measure the temp of the boiler and not the actual water, and therefore not in contact with the water inside?

Secondly for the brew temperature is it measured at the group head or at the boiler, as I presume there will be a couple of degrees difference between the two, i.e. if certain coffees are recommended to be pulled at 94c, and my pid on the boiler is reading 94c will the water at the brew head actually be around 91-92c?

hope these questions made sense,

chris


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## Glenn (Jun 14, 2008)

A decent PID will give you boiler temperature. You will have to account for heat loss and the offset temperature at the grouphead.

There can easily be a few degrees difference.

You may need to use a Scace to determine the actual offset amounts.


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## RoloD (Oct 13, 2010)

chrisalmond said:


> Firstly the thermocouple itself, when I unscrew the old thermostat will I get water gushing out of the boiler, or does it only measure the temp of the boiler and not the actual water, and therefore not in contact with the water inside?
> 
> Secondly for the brew temperature is it measured at the group head or at the boiler, as I presume there will be a couple of degrees difference between the two, i.e. if certain coffees are recommended to be pulled at 94c, and my pid on the boiler is reading 94c will the water at the brew head actually be around 91-92c?


 The thermocouple screws into the wall of the boiler - water will not gush out.

But you have put your finger on one of the limitations of a PID system on a thermoblock machine - you are not measuring the temperature of the water passing through the coffee, you are not measuring the temperature of the water in the boiler, you are measuring the temperature of one part of the wall of the boiler. Now those temperatures may not be far apart, but I would argue that the offsets between them will vary as water is flushed in and out of the boiler and steam is pulled.

If you think you are going to control the brew temperature of the water to within a degree, you will be disappointed. A PID certainly does increase the temperature stability of the Classic and it is a great modification, but to think you can tweak the temperature by the degree is a fantasy.


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## chrisalmond (Jan 18, 2013)

Thanks for the quick responses.

this leads to another question out of curiosity, how could I measure the temperature at the grouphead, and what advantages are there of this?

This is not for the PID, but I have had another idea instead of using a PID and it should be able to give me multiple temp readings.


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## lookseehear (Jul 16, 2010)

I had a PID on my classic, and while it isn't a perfect solution it added so much consistency to my shots.

The way I measured the offset is to set the PID to something like 103, let it stabilise (if this is just after you have switched the machine on wait half an hour) then flush water through the group and watch and listen closely. If it flashes to steam or 'spits' then the water temp is above 100 so move it down one degree, leave it ten minutes and try again. If it didn't flash/spit at the group at all then move it up one degree then leave it ten minutes and try again.

What you want to do is establish the first setting where the water is slightly flashing at the group. This will be your 100 degree setting. If this happens at 105 then your offset will be 5 (I think some PIDs treat this as a +5 setting and some as a -5 setting - check your manual).

Once you have set the offset then move the temp back down to 93 if you use lighter roasts or 91 if you use darker roasts and go from there.


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## RoloD (Oct 13, 2010)

I should add, Chris (if Chris is your name), that my comments were a combination of speculation and my own experience of fitting a PID control to a Gaggia. I'm not a scientist.

I think the problem is not so much how to measure brew temperature (and the only relevant temperature is that of the water as it actually passes through the coffee) but how to maintain temperature stability from one shot to the next. All a PID is doing is flicking the power to the boiler on and off; heat is not going to flow instantly from the boiler to the water, the temperature of group itself is going to affect the temperature of the water passing through it and, unlike a commercial machine, there is nto enough mass of metal to maintain a stable temperature. PIDs do a good job in stabilising temperature in a themoblock machine, but they don't work miracles.

There are such things as (expensive) SCACE devices that measure the temperature in the brew head (no one here seems to be selling them at the moment). Reiss at Londinium was talking about bringing out a low-cost app controlled device to do the same.

Roland


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## chrisalmond (Jan 18, 2013)

I was also thinking of something a little more advanced than just a PID, even though I have just bought one. I have been looking into using a Raspberry Pi micro computer with a coffee machine. There is a gréât project called BrewPi for those into homebrew beer making. Looking at there project it would be simple-ish to adapt there work, and would meen that several seniors could be used on the same machine, and could also register all read outs in graphe form, and all connect by bluetooth to an iphone or a smart phone. This is just a pipe dream at the moment as like many of you I do not have the time to invest into a project like this at the moment.

Any of you know of any projects like this at the moment it would be great to hear from you.

Chris


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## tribs (Feb 21, 2012)

This guy made an advanced PID with an Arduino Controller

I can maybe give you some tips on your DIY PID, I am presuming you are doing this on a Gaggia Classic.

I found the original location of the thermostat to be less than ideal for the PID TC. I decided to use a wire type TC because it reacts more quickly. With this I realised that the thermostat housing was too close to the left side heating element and the temp measured was shooting up and down when the element had power applied. You probably wouldn't notice so much on a standard ThermoCouple, but you'd still have the temp influenced by the heating element. I have mine positioned at the back of the boiler, central (as far from the elements as possible) and just above the bottom of the boiler where there is the lip that is attached to the group. I found this to be the best balance of group and boiler temperature and even with the fast reacting TC is slow to rise and fall. You have to get creative with how you attach it though. I currently have it stuck on with a blob of blu-tack. I stuck some Alu foil tape over that, but a few days later opened the case and found the tape had curled into a tiny ball of aluminium







. The blu-tack is still there. I'm sure it's possible to get some heat resistant tape. Disclaimer: Be aware that if it falls off the PID may fire the heating elements constantly and overheat the boiler, blowing the one-time thermal fuse, or doing other permanent damage.

The next tip I have is to rig up a DIY Scace type PF temp measurement. If you have a new Classic with pressurised PF basket this is quite easy. You will need another wire type TC and a controller for measuring it. I have a TM-902C. These are a few quid on ebay from Hong Kong and China.

Take the PF and thread the TC through the spout. Thread it through the hole in the side of the black plastic thingy (Crema Perfetta) so the probe sits in the cup. I have a pic of this, I will try and dig it out. Place the black thing in the PF spout hole and the pressurised basket on top. Engage the PF and place a cup under the spout. Hit the brew switch. The temp reading will be the temp of the brew water (or very close to it). You see the whole point of the pressurised basket is to provide the resistance to slow the flow of water through the coffee. It leaves the basket through the hole in the bottom and straight into the cup of the black plastic thingy. It's still a little too fast for my liking. Maybe the single basket is a little slower. You can slow it down more by maybe putting coffee in it or a perforated rubber blanking disc or sweet wrapper. Use your imagination. Do some experimenting to determine your offset (PID), startup warming and recovery times. And of course enjoy your coffee


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## chrisalmond (Jan 18, 2013)

Hi Tribs,

I like the idea of putting the TC on the outside of the boiler, as then I do not have to mess about with 4m screws, may try blue tac or try to find some sort of tape that can take the heat. Just on question on your solution if I may, what temp readings are you getting, from both your PID and the the GH?

And thanks for the Info on the Arduino controller

Chris


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## tribs (Feb 21, 2012)

chrisalmond said:


> Hi Tribs,
> 
> I like the idea of putting the TC on the outside of the boiler, as then I do not have to mess about with 4m screws, may try blue tac or try to find some sort of tape that can take the heat. Just on question on your solution if I may, what temp readings are you getting, from both your PID and the the GH?
> 
> ...


If the group and PF is fully warmed up (20-30 mins), I actually find the offset is zero so that is what I have it set at. But I think my PID reading is 2 or 3 degrees Celsius lower than actual. My TM902C is ~2.2 degrees lower too (I am not sure if the controller or TC is responsible for the errors). You can check with a more reliable thermometer or you can calibrate with boiling water. Currently I have my PID at 95C, but I change it depending on the coffee. I generally like dark roasts at 90-93C, lighter roasts anything from 90-98C. If I am finding my shots too acidic and I can rule out channelling or the shot is not too quick then I up the PID setting a couple of degrees. If it lacks sweetness, I go the other way.


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## origmarm (Mar 7, 2012)

I have the Auber PID on my Classic and I second Rolo's comment that if you think you are going to control the brew temperature of the water you will be disappointed. That said the PID certainly adds stability and I was pretty impressed with the change in the steaming capability (primarily I think due to the fact that it kicks the boiler on much earlier). Worth noting that Auber deliver a document with their PID that features a study on PID setting vs brewhead temp and other variables. I've mainly used that and found their suggested starting point of 103 to be about right.


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## chrisalmond (Jan 18, 2013)

So then cheap 15euro pid fitted, and seems to be working well! Just got to find a case for it to fit it to the side of the machine. Was surprised how easy (and cheap) it was to fit a PID. Using bluetac at the moment but working on a better solution. 103 seems to be a bit hot, may try to cool it down a bit, though wish hasbean would put ideal brewing temps on their beans just to give me a starting point. Has anybody had experience of the temperature guns, they seem to be quite cheap now on amazon, maybe a solution for measuring brew temp???

cheers chris


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## tribs (Feb 21, 2012)

I'd say 103 is too hot if you are using the position I recommended. Try about 95-96C. Are you using a wire-type Thermocouple?


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## bronc (Dec 10, 2012)

I found adhesive tape which is rated for temperatures up to 105*C. How hot does the outisde of the boiler get especially when steaming?


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## lookseehear (Jul 16, 2010)

Too hot - more like 125 degrees when steaming.


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## bronc (Dec 10, 2012)

Ahh.. Well, if I don't find something which is rated for higher temperatures I'll go with the Blue Tac probably.


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## Glenn (Jun 14, 2008)

The higher temps are read at the boiler usually. There is usually an offset of 5+ degrees to the group in home machines. This a 103c reading at the boiler could translate to 95c (or less) at the group


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## osrix (Feb 15, 2013)

Just reading through the thread, I would recommend a product called Sugru http://sugru.com/questions/can-sugru-stay-solid-at-137c to semi permanently place the thermocouple.

Its a silicone putty the sets like mastic and is fully removable - but is apparently quite heatproof too! Ive used a lot for a few things but it seems like a great and less messy alternative to bluetack.

I was reading through to get an idea of PID mod to my Classic and whether its worth the expense. I love the the thought of an Auber set-up with pre infusion but for $200 I must make more sense to buy a better machine...

Hope the link is helpful to all in any case!!


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## tribs (Feb 21, 2012)

That Sugru looks good. It might be useful for other apps too.

Blutack actually does a reasonable job. It's heatproof, and it seems to set fairly hard after heating, it's just it's stickyness comes into question. If it's stuck on a vertical surface, it's liable to fall off. Fortunately, I have mine placed on the lip at the bottom of the boiler.


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## osrix (Feb 15, 2013)

tribs said:


> That Sugru looks good. It might be useful for other apps too.
> 
> Blutack actually does a reasonable job. It's heatproof, and it seems to set fairly hard after heating, it's just it's stickyness comes into question. If it's stuck on a vertical surface, it's liable to fall off. Fortunately, I have mine placed on the lip at the bottom of the boiler.


The stuff is pretty amazing, Ive used it for all sorts of fixing and sticking, the great thing is it sticks but can be scraped off if needed.


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## bronc (Dec 10, 2012)

I installed my PID over the weekend putting the thermocouple where tribs suggested it. I find my PID having issues adjusting the temperature though. It overshoots a couple of degrees and I wonder if this isn't due to the distance of the TC to the heating element. Can any of you guys with a Sestos post his settings for M50, P and t?


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## painty (Jul 25, 2011)

Have you run the autotune/self-tune sequence (assuming it has one)? That should correct the overshoot.


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## Kyle548 (Jan 24, 2013)

I decided I'm just going to tap the thermowell in the boiler and put a 6mm TC into it.


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## bronc (Dec 10, 2012)

painty said:


> Have you run the autotune/self-tune sequence (assuming it has one)? That should correct the overshoot.


Yes, I did but it didn't help.

Kyle, what TC are you going to use? The one that comes with the Sestos kit? I'm thinking of sticking in the wire one in the hole of the thermostat and sealing it off with some Sugru.


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## Kyle548 (Jan 24, 2013)

bronc said:


> Yes, I did but it didn't help.
> 
> Kyle, what TC are you going to use? The one that comes with the Sestos kit? I'm thinking of sticking in the wire one in the hole of the thermostat and sealing it off with some Sugru.


If you did that, be sure to add a lot of thermal compound before you add the sugru.

Something like Arctic Silver, which is unconductive.

My PID wont have a TC with it, I don't think....

I just bought a cheap amazon one with a 6mm thread.

don't know how hard it will be to tap the thermowell though.


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## El carajillo (Mar 16, 2013)

As long as you use the correct size drill and tap I would have thought it would be a straight forward job,especially as the metal is soft.


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## Kyle548 (Jan 24, 2013)

El carajillo said:


> As long as you use the correct size drill and tap I would have thought it would be a straight forward job,especially as the metal is soft.


If I use a 6mm bit then an m6 tap, will it work?

I'm concerned about tap vs drill bit size.


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## painty (Jul 25, 2011)

Looks like it's a 5 mm drill for an M6 (coarse) thread. Google 'thread tapping drill size' for the tables.


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## Kyle548 (Jan 24, 2013)

painty said:


> Looks like it's a 5 mm drill for an M6 (coarse) thread. Google 'thread tapping drill size' for the tables.


That saved me a potentially troubling situation.

Thank you.


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## painty (Jul 25, 2011)

Is this something people have done before by the way? Are there guides out there? Just thinking it's going to need to be well sealed as it'll see the full brew pressure.


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## Kyle548 (Jan 24, 2013)

painty said:


> Is this something people have done before by the way? Are there guides out there? Just thinking it's going to need to be well sealed as it'll see the full brew pressure.


The thermowell doesn't go into the boiler, its just a thicker part of the boiler wall with a shallow hole for measuring boiler, not brew water temp.

I'm not planning to drill the boiler either, I'm just planning to put the TC where the tstat was, but the hole is a little too small.


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## painty (Jul 25, 2011)

Ah okay, I was thinking you meant drill through


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## Kyle548 (Jan 24, 2013)

painty said:


> Ah okay, I was thinking you meant drill through


I was thinking of doing that, but cost out weighs gain.


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## El carajillo (Mar 16, 2013)

For a blind bottom hole you will need a "PLUG" tap. These are square on the end not tapered. Taps are termed "TAPER" "SECOND" and "PLUG" used in sequence

Confirmation for hole/tap size from tables 5mm drill for6mm tap


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## Kyle548 (Jan 24, 2013)

El carajillo said:


> For a blind bottom hole you will need a "PLUG" tap. These are square on the end not tapered. Taps are termed "TAPER" "SECOND" and "PLUG" used in sequence
> 
> Confirmation for hole/tap size from tables 5mm drill for6mm tap


So, how do I tap a blind hole?

Drill with 5mm then tap with a 6mm plug tap?

What will using a second or taper tap do instead of a plug?


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## El carajillo (Mar 16, 2013)

The taps are used in sequence, as there description the taper used first to get a start as it fits into the hole.(it has almost no thread on the end) Then the second is used which is guided and forced in deeper by the partial thread formed by the taper tap. For your purpose you may be able to skip the second tap but without the plug tap you will not have a thread down to the bottom of the hole. Use some tallow or grease to lubricate and ease tapping, it also collects the swarf produced and brings it out as you back the tap out.


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