Re: [foxboro] Natural Gas Temp & Pressure compensation

Dave,

You need to know the temperature and pressure at which the orifice plate =
was designed to give you 235 inched d/p at 2000 CFM.  The compensation =
is to correct your gas flow d/p as you deviate from design pressure and =
temperature.

So when your pressure is at design pressure and your temperature is at =
design temperature,  100% from your d/p transmitter =3D 100%flow=20
or 2000 CFM.

Likely you are dealing in Standard CFM and the definition of standard =
conditions is 60 =B0F and 14.73 psia for American Gas Association based =
calculations.  This is the only place where T-ref and P-ref are =
important.

The equation below should replace T-ref with T-design and P-ref is =
replaced with P-design.

Terry


*******************


At the temps & pressures you're talking about, the scaling is linear.
Temperature is direct, pressure is inverse. Just be sure to use absolute
temperature (deg F + 460) and PSIA.

compensated flow =3D3D flow * (T-act/T-ref) * (P-ref/P-act)

T-ref is usually 60 F & P-ref is usually 0 psig (14.7 psia)

Brad Wilson
brad.wilson@xxxxxxxxxxxxxxxx
Invensys Process Systems, Inc
1090 King Georges Post Rd, Suite 204
Edison, NJ  08837
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of David Johnson
Sent: Thursday, February 28, 2008 2:04 PM
To: Foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Natural Gas Temp & Pressure compensation

Hello all,

I was wondering if someone had the formula in their back pocket for =3D

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 =
=3D

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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