What is the proper formula to use to calculate water meter efficiency on a test bench ?

[kdiehl]

Hi,
The title pretty much says it. I am using a Ford Akron test bench for the first time. I got my readings but not sure what formula to use to calculate the meter efficiency ? I'm not looking for the answer but want to learn how to calculate the answer myself. I even called Ford Customer service and they could not answer.
My test was as follows:
1/4 gpm 1 cubic foot
Meter Start-42.21 ft3
Meter Finish-43.18 ft3

2gpm 1 cubic foot
Meter start-43.24 ft3
Meter Finish-44.25 ft3

15gpm
Meter Start-44.45 ft3
Meter Finish-54.47 ft3


I realize looking at these numbers this meter is probably within spec. It was pulled from a low usage account that I found to have a bypass so I need to be able to give an accurate report with percentage numbers.
Thank You

 

[kdiehl]

Also just to add I came up with .97821553 for the first 1/4 gpm test but I am not sure I calculated it correctly and if I did then which digits would be significant in this test ? In other words would I round to 98% or 97.8% ?
Thank you

 

[bimr]

The percentage accuracy of the meter can then be read directly from the water level in the gauge glass of the calibrated tank as shown in the drawing.

http://www.fordmeterbox.com/documents/flyers/Test-Bench-Manual.pdf

 

[kdiehl]

ok, I think I was doing it wrong. It seems the formula is (tank reading/actual meter reading)x100 to get percentage ?
I need the formula so I can do more than one in the future plus it's hard to use the percentage chart on the sight glass on low flow tests. It takes forever so we use the auto stop which stops it at 1 ft3 on both low and med flow.
So if I did this correctly..
Test 1: 1/4 gpm=97%
Test 2: 2 gpm=101%
Test 3: 15 gpm=100.2%

Is this correct ?

 

[IRstuff]

Do you mean accuracy? Efficiency cannot be greater than 100%, nor is efficiency a typical figure of merit for a measuring instrument. I assume that your last measurement was based on 10 ft^3 volume.

Moreover, accuracy is typically defined as (measurement-truth)/truth and expressed as a percentage, but obviously, your test bench has other ideas.
So, your numbers should be -3%, +1, +0.2% in a normal universe

The manufacturer does not claim any accuracy specifications for the work bench, but not is perfect, but it may be that the instrument's accuracy is good enough to be negligible for these measurements.

TTFN
faq731-376

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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
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[dicksewerrat]

Run longer time frame tests.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[danw2]

I just gotta post the pic of a municipal flow meter test stand, so those of us who use error or uncertainty can see what the test is.