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Computer controlled temp and flow profiling
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andys
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andys
Joined: 10 May 2003
Posts: 857
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Sun Aug 11, 2013, 11:21am
Subject: Re: Computer controlled boiler temp - better than PID?
 

jonr Said:

My experience with HX was that while it did naturally have a drop during brew, the starting brew temp was so effected by flush, incoming water temp, flow rate and ambient temp that I had no interest in keeping it.  For me, a low cost Gaggia Classic plus $30 worth of controls is producing much better results.

Posted August 11, 2013 link

When you say "better results," do you mean "better" temperature measurements or better tasting coffee?


jonr Said:

A small boiler machine also has a natural temp drop.  In the case of the Classic, it's excessive unless you reduce it by bumping up boiler wall temp just before or during brew.

Posted August 11, 2013 link

My experience with the small boiler Silvia was pretty much the opposite: although the measured boiler temperature dropped radically during a shot, the delivered brew water temperature (which is what you are ultimately trying to control) was pretty stable. I believe others found the same thing:
https://groups.google.com/forum/?h l=en#!topic/alt.coffee/zitTYJZpe8c

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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jonr
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Joined: 25 Jun 2013
Posts: 298
Location: Americas
Expertise: I like coffee
Posted Sun Aug 11, 2013, 12:14pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

> When you say "better results," do you mean "better" temperature measurements or better tasting coffee?

I'm pretty consistently getting shots that taste as good or better than my very best HX shots - without all the not so good shots that the inconsistent HX was producing .   While there is some rough consensus on a range of ideal temperatures, once into that range, I don't know what "better" is yet.

My sensor is on the top of the boiler vs down low.  The idea was that this more accurately reads the temp of the water just before it exits (although it still has to drop through the tube).  I don't know about other boilers - if the sensor were near the cool water intake, I would expect big drops in what the sensor sees even as output temp stays fairly constant.  

A drawback to many machines with larger single or double boilers is that you can't get a temperature drop if you want it.
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jonr
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Posted Sat Aug 17, 2013, 1:22pm
Subject: Re: Computer controlled boiler temp - better than PID
 

I added a fast warmup function (< 3 min although the ~8 second flush is still manual), control of steam temp and the ability to log values from a second temp sensor (ie, basket temp).  I'm considering adding a DC SSR to allow control of pump power (and thereby pressure and flow).  

A far out concept is to add a computer connected scale under the cup to allow real-time closed loop control of flow.   Ie, one might be able to always get 30 ml in 25 seconds even if the dose and tamp are off a little bit - just adjust pressure as the shot progresses to make sure you end up there.

In general, I think that consistency is an important goal for espresso machine improvement.
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jonr
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Expertise: I like coffee
Posted Tue Aug 20, 2013, 8:36am
Subject: Re: Computer controlled boiler temp - better than PID
 

I put a lightweight PT1000 basket temp sensor in today and am getting approximately the 94C dropping to 91C profile that I wanted to start with.
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jonr
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Posted Thu Aug 22, 2013, 11:33am
Subject: There is no such thing as "boiler temperature"
 

Today I noticed that the stainless steel case acts as a cooling fin until it gets fully warmed up.  Temperature at the top of the boiler may be perfect, but the case can cool the group head and the bottom of the boiler.  The result is increased stratification in the boiler and brew temperature that is low by > 3 degrees (I definitely did not like the taste).

A longer warmup reduces the effect, but I suspect that changes in room temp will always effect the delta between a boiler wall sensor and the actual brew temps.  OK, confirmed.  A fan blowing from across the room dropped brew temp by 3C, even while the computer was holding the temp it saw perfectly constant.

More confirmation:  http://www.espressotec.com/commercial/index.php/resources/?p=503
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D4F
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Joined: 15 Mar 2012
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Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Thu Aug 22, 2013, 7:32pm
Subject: Re: There is no such thing as "boiler temperature"
 

Yep, that is why 15+ minutes of warmup needed.  The group fastens to the case, vs well insulated from the case, so heatsink.  AndyP noted that in the PID thread and said that he liked the cheaper plastic cases if he wanted fast warm up.  Temperature at the sensor, and sensor only, is maintained by the PID or computer, as I am sure you know, thus the false sense of stability at the readout in only several minutes.  The sensor and boiler on Gaggia are close to the same, but the sensor is really what is read.  You have given a good reminder of why a machine needs to warm up in spite of the apparent temperature reading.  Again, I know that you know this but emphasize for those reading.

The fan moving air across the group may be more effective cooling than a few degrees of room temperature change in stationary air.

The only reason I know for trying for a "stable" brew temperature is to gain and demonstrate control.  Once you realize that you can stabilize, then the trick is to control the hump/drop.  That comes back to taste and the cup, not precise computer or PID control on a graph.

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
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Joined: 25 Jun 2013
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Location: Americas
Expertise: I like coffee
Posted Fri Aug 23, 2013, 10:48am
Subject: Re: There is no such thing as "boiler temperature"
 

I would say that 15 minutes of idle (no flush or shots, no steaming, no changes) seems to be enough to get a reasonably consistent temperature throughout the boiler.  Less than that (say back to back shots) may need some compensation even if the machine is thoroughly warmed up.  Ie, it's probably important to think in terms of both case warmup and boiler stabilization.

I'm going to implement open loop pump power control.  Programmable pre-infusion, ramp up, pressure profiling (probably not very accurate with no flow or pressure feedback) and auto turn off are interesting.  Plus, variable pump power makes it easy to get exactly the right flow rate for testing temperature profiles without having to use some type of puck simulator or restricting valve.  Software design will be similar to temp - a table of % power vs time.
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jonr
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Location: Americas
Expertise: I like coffee
Posted Sun Aug 25, 2013, 2:42pm
Subject: Re: Vibe pump control
 

I looked into flow control with a vibe pump.  While some (thanks Andy) have reported good results with dimmers or resistors, I'm not convinced that chopping off the beginning of each waveform or reducing the voltage level is ideal.   I'd prefer to use a full wave bridge rectifier(4 diodes) and a capacitor to get DC and then use a DC SSR to produce any frequency and duty cycle.  

Simpler (ie, fewer parts) would be just a SSR to skip entire cycles.  Ie, for 75% power, skip every fourth 50/60 hz cycle.  With this option there is also the issue of synchronization with the wave-forms.   Normally the computer isn't synchronized with AC power and you have to consider that you might turn on part way into a pulse.  Plus you get more pressure fluctuations.

I'm producing nice graphs of temp profiles and continuing to try variations.
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billc
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Joined: 15 Jan 2009
Posts: 131
Location: Seattle, Washington
Expertise: Professional

Espresso: CC1 - GS - GS3 - GB5
Grinder: Baratza - Mazzer-Marzocco
Drip: My own Creation
Posted Mon Aug 26, 2013, 6:44am
Subject: Re: Vibe pump control
 

jonr,
you are correct about using computer (software timing as the clock) control possibly skipping, or missing, a zero cross.   You will need a real time system or some other hardware timed system to do this (>200hz).  Be careful after you rectify the AC because you end up with about 160VDC.  You probably already know this but thought I would put it out there.

Skipping cycles has not worked for me.  It did not perform well enough to consider this method for brewing ( I do use it to push water through the steam boiler in pulses however).

Rectifying the AC should be interesting.  It would be a bit expensive to implement with lower cost machines but would offer you the most control.  I have components to do this if you need some.


BillC
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jonr
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Joined: 25 Jun 2013
Posts: 298
Location: Americas
Expertise: I like coffee
Posted Mon Aug 26, 2013, 9:21am
Subject: Re: Vibe pump control
 

Bill, what happens with cycle skipping?  Does it cause pressure to become too unsteady?  

With further research (like Bill's nice vibe pump video), I think peak voltage is what determines how far the spring in the pump gets compressed and thus how far it moves with each stroke.  So perhaps lower voltage would be best to control pump output (flow).  High speed PWM would do this, no need for flat DC.  It looks like SSRs aren't fast enough, so would have to use a MOSFET or IGBT.

If only these pumps had a slightly different design where the volume per stroke was fixed.   That might eliminate the need for a flow meter.
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