# Need assistance verifying calibration on a flow meter.

#### SMF

Hi everyone,
I need to verify the calibration of a Foxboro IDP-10. It's measuring low pressure header air at 7 psi and the range of the meter is 0-1200 CFM. The meter is using the square root extractor which is preventing me from checking the cal. I would like to check at 25% (375 cfm) 50% (750) 75% (1125) and 100% (1200). Is this linear check acceptable, I tried it with a Fluke calibrator and at the low end the numbers were way off but at 100% I was spot on (is this the sr rt at work?). I'm pretty sure the square root is doing what it's supposed to do but I don't completely understand how to run a verification/cal with the sq rt.
What's more the Fluke calibrator is measuring in PSI. It's my understanding that flow and pressure are proportional so I feel I'm on the right track using PSI to verify CFM.
What is the proper way to verify calibration on this instrument?
Thank you kindly.

#### David_2

I presume the IDP-10 uses pressure units for its LRV and URV pressure settings. What are the LRV and URV for this application (including eng units)?

Does the transmitter have a local indicator or are you reading the CFM on a remote display/PLC-HMI ? If it has a local indicator, how the indicator scaled?

#### SMF

HI David,
The LRV=0, URV=1200 eng units programmed in the IDP-10 are cubic feet per minute. There must be an internal conversion taking place from the pressure against the diaphragm converting the signal to cubic feet per minute because there are no pressure eng units available only volumetric. The transmitter has a local digital display displaying the flow rate in cubic feet per minute. I don't have the option to scale the display.
Thanks again.

#### David_2

Assume the transmitter is configured properly, so 4-20mA = 0-1200CFM in square root mode.

The Sq rt of the normalized percent of max DP = percent of max flow

375 CFM, 25% of max flow rate of 1200 CFM, is generated at 6.25% of max DP
[Sq rt of 0.0625 = 0.25 = 25.0% max flow]
6.25% of 4-20mA = 5.00mA

750 CFM, 50% of max flow of 1200 CFM is generated at 25% of max DP
[Sq rt of 0.25 = 0.50 = 50.0% of max flow]
25% of 4-20mA = 8.00mA

1125 CFM, 75% of max flow rate of 1200CFM is generated at 56.25% of max DP
[Sq rt of 0.5625 = 0.75 = 75.0% of max flow] (this line has been corrected from first posting)
56.25% of 4-20mA = 13.00mA

#### SMF

Dave, I trying to follow the math and as printed it looks good but I can't figure out how you are finding the generated percentage ( ie 6.25%, 25%, 56.25%). Please explain.

#### BobM

Dave, I trying to follow the math and as printed it looks good but I can't figure out how you are finding the generated percentage ( ie 6.25%, 25%, 56.25%). Please explain.
25% Input differential pressure - 50% MA Output..
50% input differential pressure - 70.70% MA Output..

Sqrt 25= 5, 5x10 = 50%
Sqrt 50= 7.071, 7.071x10 - 70.71

There is also a Setup for a Foxboro Flow Meter on You tube for a IDP-10..
I get it for you and maybe it will Help..
Watch that Video and see if it Helps
Take care, Bob

#### SMF

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