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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Wed Aug 7, 2013, 8:45am
Subject: Re: Computer controlled boiler temp - better than PID?
 

> You have automated the steam switch flip at the beginning of the brew

Just to be clear, it allows far more flexibility than that.  Think two switch flips every 1/2 second from 10 seconds before the brew and all throughout the brew.  All 160 timed accurate to .01 msec.

It would cost $6 to add a 2 line LCD display and more buttons.  This would allow adjustability without using a laptop.  There are some interesting things that could be done by adding a flow sensor.  I'm considering adding another SSR to add timing to my grinder (I'd like to avoid using a scale).

I put in the "next morning auto turn on" feature last night.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,981
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Wed Aug 7, 2013, 9:52am
Subject: Re: Computer controlled boiler temp - better than PID?
 

jonr Said:

> You have automated the steam switch flip at the beginning of the brew

Just to be clear, it allows far more flexibility than that.  Think two switch flips every 1/2 second from 10 seconds before the brew and all throughout the brew.  All 160 timed accurate to .01 msec.

It would cost $6 to add a 2 line LCD display and more buttons.  This would allow adjustability without using a laptop.  There are some interesting things that could be done by adding a flow sensor.  I'm considering adding another SSR to add timing to my grinder (I'd like to avoid using a scale).

I put in the "next morning auto turn on" feature last night.

Posted August 7, 2013 link

PID also adds heat during brew, the equivalent of steam switch flipping on and off.  It is through a second alarm function and trying to reach a second temperature but non the less switches heat on and off via the SSR. The interval approach seems more precise, but the on and off of the heaters from hysteresis around the set temperature seems to work, intrashot is fairly stable.  Of course you have to estimate and calculate the amount of heat added and with PID the alarm set point and hysteresis determine the amount of duty cycle or on time, the switch fip equivalent.  With PID approach it takes a bit of trial and error to get that proper temperature and changes with significant shot volume change, as potentially your system will.

Great to here that LCD and control can be added.

I am sure that you will add more function as you use the system, already looks like you are :)

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Wed Aug 7, 2013, 5:41pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

For anyone interested in just pretty accurate and flat intra shot temperatures from a Gaggia Classic, I would simply add a thermometer and use the techniques that AndyPanda shows here:

http://youtu.be/GFVTp4Jgo5k

I think it's when you want 1 degree or better accuracy, non-flat profiles or convenience features that you need something more.

It's not clear to me how much effect ambient temp has on the temp that a boiler wall sensor reports.  That's something that I may adjust for.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,981
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Wed Aug 7, 2013, 9:18pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

AndyPanda did a lot of work on temperature surfing and stability, and gave explanation and more videos here

http://coffeegeek.com/forums/espresso/machinemods/571792

Page 8 - 11 and a couple of other videos

http://www.youtube.com/watch?v=qDXjjjoYRsU

http://www.youtube.com/watch?v=Wo97AGMLqb0

He also talked about the Polder thermometer and how to use it.  He did about as well as the PID and other devices.  Makes me wonder how precise it all has to be.  OTOH, you need a lot of practice and skill to control as well as he did.

WRT ambient temperature, a probe inside the case of the Classic showed essentially no changes once the boiler and machine heated up for about 20 minutes.  I was asked about temperature inside and the wiring.  Pretty stable temperature when I used a second thermocouple and let it just monitor ambient.

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Thu Aug 8, 2013, 10:41am
Subject: Re: Computer controlled boiler temp - better than PID?
 

I suspect that ambient temp is why people let machines warm up for so long.  The Gaggia Classic has enough heater power to bring the boiler from room temperature to desired temp in < 2 min.   So why 20 min warm ups?  At 2 min, the air around the boiler is still pretty cool and significantly effects the boiler wall temperature reading.  Ie, there is a different temp offset between the boiler wall and the water - and a few degree error in water temp impacts coffee taste.  If it could be made to work well, a 2-5 min warmup would be of some convenience value to me.

> a probe inside the case of the Classic showed essentially no changes once the boiler and machine heated up for about 20 minutes.

The question is not only if it's eventually stable over time, but is it fixed at different room temps?  Ie, what happens to inside the case temperatures when room temp varies from say 77F to 70F (typical summer to winter values for me)?  If inside the case temp does vary with room temp, how much effect does it have on the boiler wall temp to basket water temp offset (30F?)?  Does steam then brew vs brew then steam effect inside the case temps enough to matter?

Another ambient temp issue is reservoir water temp.  I'm sure its temperature effects temp during brew.
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Thu Aug 8, 2013, 2:03pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

Here is a speculative feature.  Say I put a semi permanent probe in the basket and had the computer always measure basket temp vs time.   I'm sure that trying to adjust this temperature in the fly won't work (far too much lag).  But how about for the next shot?   Say that during seconds 10-15 of the brew period, there is a little temp sag.  Maybe the heat vs time table could be automatically bumped up a little to fix this.  Ie, self tuning for future shots based on the results of previous shots.

Another way to look at this is that while I have a flexible heat vs time table for the brew period, I don't know exactly how it translates into temp vs time (what really matters).  I can run a number of test shots and manually adjust the table, but I like it when computers do the work for me.
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ddubick
Senior Member


Joined: 1 May 2012
Posts: 142
Location: Calgary, Alberta, Canada
Expertise: I live coffee

Espresso: Nuova Simonelli Appia 1Gr
Grinder: OE Pharos, Macap M5, Nuova...
Roaster: Behmor 1600
Posted Fri Aug 9, 2013, 7:55am
Subject: Re: Computer controlled boiler temp - better than PID
 

Interesting read, I don't know if I agree with your methods but thanks for bringing those Freescale Freedom boards to my attention.  I had been basing my project around Arduino boards but this looks like these might be better suited.  I like how you can get very small Arduino boards (nano and pro mini) but there are some definite drawbacks to the onboard ADC when doing temperature sensing.  Ordered 2 FRDM-KL25Z boards from Newark on Wednesday and got them yesterday (great turnaround for $8 shipping).  Played around with it last night before bed.  What are you programming them with?  I decided to try mbed first as I read a good review on it.  Haven't tried the Coocox IDE that came with it yet.
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Fri Aug 9, 2013, 8:11am
Subject: Re: Computer controlled boiler temp - better than PID
 

I've been using mbed - let me know if you have any questions about it.  I'd only go back to Arduino if size was an issue or there was some particular library I needed.
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Fri Aug 9, 2013, 8:33am
Subject: Re: Computer controlled boiler temp - better than PID
 

I looked at the ambient effect on in-case temperature.  I didn't try different room temps yet, but I did measure a ~6F degree drop when there was a low speed fan blowing from across the kitchen.   As a percentage of the delta, that comes out to a ~2F change in the offset between boiler wall temp and boiler/basket water temp (but that's pretty speculative and needs verification).  2F isn't big but it would effect espresso taste.

If room temps are warmer/cooler than normal, bumping down/up the temp a degree or two from your usual value makes sense.

Today I added some code to the open loop brew section to account for steady-state power needed to maintain boiler temp (a proxy for ambient temp) and adjust for water tank temp (which I take from the boiler temp when first turned on - with sanity checks).  Minor tweaks, but important if 1F accuracy over various conditions is the goal.

Edit: the initial temperature of the ground coffee also has  as significant effect on the temperature seen by the coffee further down in the puck.  So yet another ambient temp effect that needs offsetting.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,981
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Fri Aug 9, 2013, 9:44am
Subject: Re: Computer controlled boiler temp - better than PID?
 

You could fix that if you determine that it matters with something like this Silvia wrap.

http://www.pidsilvia.com/insulation.htm

Why would the PID or your board not just add the appropriate amount of heat to keep the boiler at set?  My PID seems to hold its set temperature summer and winter, with house temperature changes, and I do not measure different thermofilter temperatures.  I have seen other threads about changing PID set to accommodate insulation and IIRC it was not needed.

 
D4F also at
http://www.gaggiausersgroup.com/
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