Re: [foxboro] Natural Gas Temp & Pressure compensation

The following is based on ideal gas approximation and flows measured by
differential pressure.  It will work well for natural gas, nitrogen, air,
etc.  Do not use it for steam.

First, as is always the case for flows measured via differential pressure,
make sure you are performing exactly one square root extraction on the D/P
signal to read volumetric (uncompensated) flow.  This square root
extraction can be configured in the transmitter, or via use of SCI = 5 in
your AIN block, but not both at the same time.

Next, Compensation factor = sqrt ( (P/Pd) * (Td/T) ), where:

P = measured pressure (absolute units)
Pd = design pressure (absolute units)
Td = design temperature (absolute units)
T = measured temperature (absolute units)

To determine design temperature/pressure, look at the spec sheet and/or
flow calculation for the flow element.

To convert units to absolute:
      deg R = deg F + 459.6
      psia = psig + 14.7

Your final compensated flow is the uncompensated flow times the
compensation factor.

Greg Hurwitt
BASF Corp.
Freeport, TX




                                                                           
                         David                                             
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Hello all,

I was wondering if someone had the formula in their back pocket for
taking a DP on a natural gas line and converting it to a compensated flow.

I have a DP orifice plate that is scaled from 0-235 " water.
This, I
am told corresponds to  0-2000 CFM.
I have a PT scaled from 0-130 PSI
I have a TT scaled from 0-300 deg F.

So a DP of 100" H2O at 80 Deg F and 100 PSI is ??????SCFM.

So can one of you Chemical Engineers lend a hand?

Thanks,
David






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