Gicar flowmeter accuracy - Page 2

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Peppersass
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#11: Post by Peppersass »

AssafL wrote:Also, looking at the Nozzle specs, it would seem to me LM chose a nozzle size of (probably) 3.7 mm which would be strange since Gicar recommends to a value centered around the expected flow. At 500ml/min one would assume Gicar would recommend and 0.7 to 1mm nozzle.
Where is this nozzle supposed to be located? Doesn't the 0.6mm gicleur ahead of the flowmeter effectively act as a nozzle to slow the flow rate?

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AssafL (original poster)
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#12: Post by AssafL (original poster) replying to Peppersass »

The nozzle is inside the flowmeter (probably part of the casting). It isn't an external part. I think it increases the water flow velocity so it will turn the propellor.
Scraping away (slowly) at the tyranny of biases and dogma.

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Peppersass
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#13: Post by Peppersass replying to AssafL »

It's on the inlet side, then. Maybe LM didn't want a small diameter nozzle to affect the overall flow rate, though I guess if the nozzle were the same size as the gicleur it wouldn't.

I recall Bill Crossland saying that the flowmeter in the GS/3 isn't accurate enough for profiling. I also recall HB member Jacob built an Arduino-based profiling system using the flowmeter. His early tests seemed to indicate that it would work, but I don't know how it's behaved in the long run. Haven't seen a post from him in a while. You might try a PM to see if he's still around.

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Jacob
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#14: Post by Jacob »

Peppersass wrote:... His early tests seemed to indicate that it would work, but I don't know how it's behaved in the long run.
Perfectly - Try it out :wink:

(my system is an automated system based on readings of my build in GS/3 flowmeter)

But I found the flowmeter useless for estimating the brew weight - I couldn't find an algorithm that would cover even a small verity of shots!

Billc
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#15: Post by Billc »

The Gicar Flow meter is fairly consistent if you are talking about the complete dose of water. This type of Flow meter is good for a constant flow rate and the data sheet describes this.

For flow profiling to be consistent you need a higher resolution "tick" count. This can be accomplished by replacing the 2 magnet turbine with a 4 or 6 magnet turbine in the existing design or use something that have a higher resolution. The current design has a bit of bypass and it varies depending upon the flow rate of the water.

BillC

jonr
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#16: Post by jonr »

I would guess that software techniques such as accurate time stamps on rising and falling edges, interpolation, table lookup linearization (tick period vs flow rate), etc would also help.

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Jacob
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#17: Post by Jacob »

What kind of accuracy is actually needed?
With what kind of accuracy does the rest of the system respond?

Bill & Co knows what they are talking about, no doubt about that, but IMHO the Gicar is accurate enough to play around with.
With everything hooked up as a pressure profiling setup or similar, it's only a matter of a few hours of programming :wink:

BTW I'm using time stamps on both rising and falling edges. This gives me a total of 200-240 ticks for the complete shot and 3-20 ticks a second during the shot.

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AssafL (original poster)
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#18: Post by AssafL (original poster) replying to Jacob »

My intention was to use a scale to measure the weight of the shot, and to use the Gicar to measure the amount of water that went to the puck. The difference should be the amount of water absorbed by the puck, which I assume should allow me to deduce the weight of the dry coffee puck.

Why do this? Well, a scale with an RS232 output, and the Gicar flowmeter, (if it was accurate) one could theoretically program the button NOT FOR VOLUME but for a specific BREW FORMULA. So one could have a button for Ristretto, that would always pour a specific EBF whatever the dose happened to be.

Unfortunately, the GICAR flowmeter did not seem accurate enough, albeit I still have to test it with a controlled pressure at the input to see if regulated pressure compensates for different flow rates. Doesn't seem like it meets the specs at all....
Scraping away (slowly) at the tyranny of biases and dogma.

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AssafL (original poster)
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#19: Post by AssafL (original poster) »

Billc wrote:The Gicar Flow meter is fairly consistent if you are talking about the complete dose of water. This type of Flow meter is good for a constant flow rate and the data sheet describes this.

For flow profiling to be consistent you need a higher resolution "tick" count. This can be accomplished by replacing the 2 magnet turbine with a 4 or 6 magnet turbine in the existing design or use something that have a higher resolution. The current design has a bit of bypass and it varies depending upon the flow rate of the water.

BillC
Actually, they have a very wide range over which it should be within 2% (according to the limited datasheet I found - it is very difficult to find Gicar stuff online - they are an obtuse outfit for anyone outside their business).

My findings were almost a 50% disparity between readings:

Test Flow rate (ml/min) Weight measured Flowmeter Pulses ml/pulse
Low flow rate 205 ml/min 106.0 grams 57 1.85ml/pulse
High flow rate 472 ml/min 102.4 grams 31 3.3ml/pulse
Scraping away (slowly) at the tyranny of biases and dogma.

jonr
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#20: Post by jonr »

It would make more sense to test at something like 30 ml/min and 70 ml/min.

With ~10 ticks/sec and flow rate re-calculated at each tick (based on time stamps), it sounds like there is good resolution for flow control - it doesn't change that fast. For example, I use a scale and only adjust pump power once per second.