Mu-T

08-26-2009, 04:43 PM

In the field, sometimes all the correct tools are not available, and we have to use what is at hand. This is the formula I use when the input gas pressure on a flow meter is not what it was calibrated for.

Variables:

AFR = Actual flow rate (CFH)

IFR = Indicated flow rate (CFH)

AP = Actual pressure (PSI) + psia constant at 1atm (14.7)

CP = Calibrated pressure (PSI) + psia constant at 1atm (14.7)

sqrt(x) = Square root of x

AFR = IFR x sqrt(AP/CP)

For example, a flow meter with a calibrated pressure value of 30, but with an actual pressure of 50, and an indicated flow rate of 35cfh, has an actual CFH of 42.108.

42.108 = 35 x sqrt((50+14.7)/(30+14.7))

I hope at some point in time this information will help someone.

Variables:

AFR = Actual flow rate (CFH)

IFR = Indicated flow rate (CFH)

AP = Actual pressure (PSI) + psia constant at 1atm (14.7)

CP = Calibrated pressure (PSI) + psia constant at 1atm (14.7)

sqrt(x) = Square root of x

AFR = IFR x sqrt(AP/CP)

For example, a flow meter with a calibrated pressure value of 30, but with an actual pressure of 50, and an indicated flow rate of 35cfh, has an actual CFH of 42.108.

42.108 = 35 x sqrt((50+14.7)/(30+14.7))

I hope at some point in time this information will help someone.