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Question about volumetric dosing?
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germantownrob
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Posted Tue Feb 21, 2012, 10:46am
Subject: Question about volumetric dosing?
 

I am playing more with weighing shots instead of just going for volume. How do machines that have volumetric dosing know how much volume to put out? Is it just a time you set to get 2oz or whatever volume you want? Or do some machines measure the actual volume? If so does it measure after the OPV?
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germantownrob
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germantownrob
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Espresso: Duetto 3, A Dead Oscar
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Posted Wed Feb 22, 2012, 8:41am
Subject: Re: Question about volumetric dosing?
 

Jwoodyu (John) responded to this question via email after asking Bill Crossland this question. I did not ask Bill if I could repost his answer so I will put what I learned from his response in my words.

There are 3 main ways for a machine to do volumetric dosing.

  1. Dosed by time
  2. Low pressure meter before the OPV
  3. High pressure meter which is after the OPV

Thank you John and Bill, this is exactly the info I was after!

Seems like the high pressure meter would be the only one that would give dosing close to weighing the shot manually. Any input from people that have a machine with a high pressure meter and have weighed the shot would be greatly appreciated.
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MARIOBARBA
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MARIOBARBA
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Posted Wed Feb 22, 2012, 8:54am
Subject: Re: Question about volumetric dosing?
 

Not sure which category my machine falls into but probably the one with the meter before the OPV since my doses aren't always the same.  If the grind or dose is off even a little when pulling a ristretto the shot is often cut short (and I measure a single dose to .01g).  I guess this is because some of the water is being diverted by the OPV after the meter measures the water throughput.  The volumetric dosing works much better when making a normal or lung.  In the end I only use the automatic feature when making a milk drink so I can focus on the steam.  When I am making an espresso I always go by eye.
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germantownrob
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germantownrob
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Posted Wed Feb 22, 2012, 9:23am
Subject: Re: Question about volumetric dosing?
 

MARIOBARBA Said:

Not sure which category my machine falls into but probably the one with the meter before the OPV since my doses aren't always the same.  If the grind or dose is off even a little when pulling a ristretto the shot is often cut short (and I measure a single dose to .01g).  I guess this is because some of the water is being diverted by the OPV after the meter measures the water throughput.  The volumetric dosing works much better when making a normal or lung.  In the end I only use the automatic feature when making a milk drink so I can focus on the steam.  When I am making an espresso I always go by eye.

Posted February 22, 2012 link

I am realizing that paying attention to bean weight and not paying attention to extraction weight allows a big variable in the actually volume. If I pull a triple into a 3.5 oz shot glass with 3/4 of the pull being crema it settles to less then 2oz by volume, so weight is the only way I can get the desired amount. In the last three years I have been fine with eyeballing the volume but I am looking to refine this. Weighing every shot is becoming a PIA, maybe a second scale would make it less so I will have to pick one up to see.

I have been wanting to upgrade for some time now but have held off trying to gather info for which machine will fit my needs and style. A high pressure meter for volumetric dosing seems to fit my style, I do want a machine that will deliver close to the amount so I don't have to weigh except for dialing in, if this is even posiable.
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MARIOBARBA
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Posted Wed Feb 22, 2012, 10:14am
Subject: Re: Question about volumetric dosing?
 

A small scale that fits under the pf may help but you would need one with very little lag or have to cut he shot before you get to the desired weight to compensate for the lag assuming a constant flow rate.
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Stuart
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Posted Wed Feb 22, 2012, 10:39am
Subject: Re: Question about volumetric dosing?
 

In response to a question about a specific machine, Phil McKnight noted (on coffee snobs .au) that the setting for a 30ml or a 60 ml dose had to be set based on a shot that was running at nearly the same speed as a regular shot:

"Not only do you have to set the volumes while you are extracting espresso, but the espresso needs to be flowing at the same or similar rate to that of your normal extractions. Faster or slower will yield differing volumes...."

At first I thought that meant it was strictly a timed dose (that's labelled as "30ml" or "60ml" by the software), but then he posted this, indicating the machine uses flow meters to determine shot volume:

"Yes it does have 2 flow meters, but neither is connected to the steam boiler. One is connected to the inlet of the OPV & the other is connected to the low pressure outlet of the OPV. Software calculates the difference between inlet & outlet and the balance is shot volume."

I'm having a bit of trouble reconciling those two statements, but assume the problem is with my understanding.
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PJK
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Posted Wed Feb 22, 2012, 10:54am
Subject: Re: Question about volumetric dosing?
 

Hi Rob,

I believe most machines with that capability have a flow-meter.  I used to have access to nice Rio HX machine at work.  It would dispense the same volume if the shot time was 10 seconds or 1 minute.  I don't know how the flow meter in it worked but it did (I suppose still does) work.

My son has a POC Starbucks Athena (which by the way they don't support anymore) which has volumetric dosing.  This machine has a little paddlewheel thing through which the brew water flows.  There is an electrical connection from the flowmeter wheel to the controller board.  I assume that the conntroler board counts pulses from the flowmeteer and terminates the shot when the count reaches some stored value.  I am sure the concept is sound and it is probably what the Rio does but I found that the Starbucs POC couldn't dispense the same volume two times in a row.

Phil



germantownrob Said:

I am playing more with weighing shots instead of just going for volume. How do machines that have volumetric dosing know how much volume to put out? Is it just a time you set to get 2oz or whatever volume you want? Or do some machines measure the actual volume? If so does it measure after the OPV?

Posted February 21, 2012 link


 
Philip J. Keleshian
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germantownrob
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germantownrob
Joined: 2 Dec 2007
Posts: 2,153
Location: Philadelphia
Expertise: I love coffee

Espresso: Duetto 3, A Dead Oscar
Grinder: Vario-W, Preciso w/Esatto,...
Drip: Brazen
Roaster: Diedrich IR-1, HT B
Posted Wed Feb 22, 2012, 1:04pm
Subject: Re: Question about volumetric dosing?
 

PJK Said:

Hi Rob,

I believe most machines with that capability have a flow-meter.  I used to have access to nice Rio HX machine at work.  It would dispense the same volume if the shot time was 10 seconds or 1 minute.  I don't know how the flow meter in it worked but it did (I suppose still does) work.

My son has a POC Starbucks Athena (which by the way they don't support anymore) which has volumetric dosing.  This machine has a little paddlewheel thing through which the brew water flows.  There is an electrical connection from the flowmeter wheel to the controller board.  I assume that the conntroler board counts pulses from the flowmeteer and terminates the shot when the count reaches some stored value.  I am sure the concept is sound and it is probably what the Rio does but I found that the Starbucs POC couldn't dispense the same volume two times in a row.

Phil

Posted February 22, 2012 link

The concept sounds sound, lol. The description I was given is the flow meter has a couple of magnets that  pass a sensor that then sends a message to the CPU which counts the pulses to determine the volume.

It makes sense to me that for this to be repeatable if it is after the OPV or else it can't account for what is being sent to the reservoir. This is not something I am finding defined in any sales description of any machine I have looked at.

As far as weighing the shot and lag time yes the scale is about 3g behind, not a big deal for me though, but the pia factor is very high. It would be very nice to have volumetric dosing that can be repeatable.
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calblacksmith
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Posted Wed Feb 22, 2012, 1:28pm
Subject: Re: Question about volumetric dosing?
 

Well, I don't know which system I have but my shots are very consistent in volume. I have no problem with that at all, regardless of how long it take to pull a shot, I get the same volume at 1 min as I do at 25 seconds.

It makes everything so much easier, if you know your volume is going to be the same each and every time then you adjust the grinder to get the shot you want. The same grind and grind volume gives me the same shot 2,3,4 or more times in a row. It makes adjusting your grinder a snap too as all you need to account for is grind and volume in the coffee, the shot will be the same so you can easily adjust one or the other (volume or grind of coffee) to get any time pulling the shot you want.

Life on the automatic side is nice indeed!

 
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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jwoodyu
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Posted Wed Feb 22, 2012, 5:02pm
Subject: Re: Question about volumetric dosing?
 

calblacksmith Said:

Well, I don't know which system I have but my shots are very consistent in volume.

Posted February 22, 2012 link

Agree 100%. If you get few factors consistent then you can adjust from that anchor. I was telling Bill a dose by weight grinder paired with a dose by weight machine would be an interesting notion. The thought being you could grind 19G and pour 38G and bang a 50% regular or there a bouts.  He politely busted my bubble and said that LM had machine at SCC that dose weight last year,  rats foiled again.

Here is link to a scale from the Christmas gift list. I ordered one in hopes of just leaving it on the drip tray.

Clicky

 
Yes i have a reason for leaving SCG off my list, yes it is my opinion, yes it is subjective as opinions are by definition, no don't start a flame war because you disagree.
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