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pressure profiling with vibe pump
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jonr
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Joined: 25 Jun 2013
Posts: 295
Location: Americas
Expertise: I like coffee
Posted Thu Aug 15, 2013, 10:07am
Subject: Re: pressure profiling with vibe pump
 

> This problem is very specific to the vibe pump since it is very flow dependent.

My guess is that one would want to use a table driven approach.  Ie, pre generate tables of %power vs pressure for a range of pucks (ie, a 3 dimensional table) and put these into the program.  As the shot progresses and you learn what %power it actually takes to maintain different pressures, you can determine a best value for the puck characteristic dimension.  Ie, use a mixture of open loop (tables) and closed loop; feedback is used to adjust behavior by 1) selecting which table is most accurate and 2) to bump up/down power levels under steady state conditions to meet the target (classic feedback control).  And of course the system should learn from each brew cycle and use the results to improve the tables for future brews (ie, inter brew auto tuning).
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jonr
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Joined: 25 Jun 2013
Posts: 295
Location: Americas
Expertise: I like coffee
Posted Sun Aug 18, 2013, 1:31pm
Subject: Re: pressure profiling with vibe pump
 

AndyPanda Said:

I started the shot letting it build to full pressure long enough to fully saturate the puck (droplets just starting to appear at bottom of basket) and then dropped the pressure and as the shot began to pour, continued adjusting the pressure (keeping it pretty low) throughout the shot to keep the trickle extremely slow.

Posted May 12, 2012 link

Based on this description, it sounds like you are doing flow profiling.  Ie, you are interested in the flow rate over time and the pump power and pressure needed to achieve the desired flow rate are secondary.
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nuwuforever
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Joined: 16 Jul 2010
Posts: 96
Location: Keizer, OR
Expertise: I love coffee

Espresso: Rio Junior HX
Grinder: Nemox lux w/stepless...
Posted Fri Sep 20, 2013, 12:39pm
Subject: Re: pressure profiling with vibe pump
 

I know the original topic is over a year old, but I'm trying to do the dimmer mod to my Oscar.  I have the exact same dimmer switch the OP installed, yet my results are really frustrating.  Two things: I'm only getting control from about the last 30% of the dimmer's range, and it's extremely sensitive.  If I go below this, the pump stalls out.  2nd, as I was calibrating my pressure, I had finally dialed in to 9 bar, but then the heating element kicked on and suddenly my pressure dropped to 5.5 bar.  That's a lot!  I'm wondering if this mod is even worth it on an Oscar, with these results.

Any Ideas?
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calblacksmith
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calblacksmith
Joined: 25 Nov 2007
Posts: 7,745
Location: Riverside, Ca, U.S.A.
Expertise: I live coffee

Espresso: ECM Vene. A1, La Cimbali M32
Grinder: Azkoyen Capriccio, Major
Vac Pot: 40s era Silex
Drip: Msl. Com. brewers
Roaster: gave it a try, decided no
Posted Fri Sep 20, 2013, 1:05pm
Subject: Re: pressure profiling with vibe pump
 

I would not do it but there is nothing wrong with playing with it I guess.
My personal opinion, a vibe pump should not be on a dimmer. I have seen a way to slow it down by changing the frequency of the AC to it VS lowering the voltage. I think full voltage and slower frequency is the way to go. However, that takes a bit of electrical know how and circuit design so it is not for everyone, or even a fraction of the reading audience.

 
In real life, my name is
Wayne P.
Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!

Feed the newbs, starve the trolls and above all enjoy what you drink!
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billc
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Joined: 15 Jan 2009
Posts: 130
Location: Seattle, Washington
Expertise: Professional

Espresso: CC1 - GS - GS3 - GB5
Grinder: Baratza - Mazzer-Marzocco
Drip: My own Creation
Posted Fri Sep 20, 2013, 8:48pm
Subject: Re: pressure profiling with vibe pump
 

A Dimmer Switch works perfectly.  However you need to purchase a decent one.  The very low cost versions will not do a very good job.  The decent dimmers work by chopping the AC signal via a random fire triac.  Essentially it senses the zero crossing of the voltage and applies a delay based upon the knob position.

You will not be able to control over 100% range.  The characteristics of the coil on the pump are non linear and the dimmers are linear.  You will only be able to control about 30-40% but it should be enough to make it look like 0-100 at the pump.    Look for the higher rated (watts) switches.  They tend to have better switching components installed.


BillC
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DeanOK
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DeanOK
Joined: 24 Sep 2012
Posts: 676
Location: OK
Expertise: I like coffee

Espresso: QM Vetrano 2B
Grinder: Vario W
Posted Fri Sep 20, 2013, 9:53pm
Subject: Re: pressure profiling with vibe pump
 

Here is a graphic image of how the triac clips the waveform if a visual helps you.

DeanOK: 92-wave[1].jpg
(Click for larger image)
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jonr
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Joined: 25 Jun 2013
Posts: 295
Location: Americas
Expertise: I like coffee
Posted Sat Sep 21, 2013, 6:19am
Subject: Re: pressure profiling with vibe pump
 

> heating element kicked on and suddenly my pressure dropped to 5.5 bar.  That's a lot!  I'm wondering if this mod is even worth it

Last week I ran without any pressure profiling and now I've gone back to a slow pressure ramp up.   Not a well controlled test, but the latter clearly tastes better to me.

The heater further dropping the voltage can be an issue; ideally a controller would measure and adjust for this.

FWIW, I am using fast PWM to lower the voltage but leave the overall waveform shape and frequency unaltered.

In general, I would encourage people to add a dimmer and try some pressure profiling.
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nuwuforever
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Joined: 16 Jul 2010
Posts: 96
Location: Keizer, OR
Expertise: I love coffee

Espresso: Rio Junior HX
Grinder: Nemox lux w/stepless...
Posted Sat Sep 21, 2013, 9:44am
Subject: Re: pressure profiling with vibe pump
 

Yesterday I had one of the best shots I've ever tasted by starting with a low flow for 2 seconds, turning off the pump via the dimmer switch for pre-infusion, then turning the pump back on at the mark I made for 9bar (though it may have been less if the heating element was on, I didn't notice).  Visually I had deep color and great tiger striping during the whole shot.  I was pretty amazed.  I have a lot to learn, but so far even with the issues I'm having, I'm already pulling better shots using the dimmer switch.

billc Said:

Look for the higher rated (watts) switches.  They tend to have better switching components installed.


BillC

Posted September 20, 2013 link

Can you recommend one?  The one I am using is a Levitron 600watt.  It's the exact same one the OP was using and it sounded like he had control over the entire range of the knob.  

I would love to find something stepped, so I can mark out the steps for easy reference.
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