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Series 820 Instruction Manual Appendix A
IM-82-C A-1
Appendix A Conversion Formulas and Gas Tables
Conversion of Flow Rate to Other T and P Conditions
The flow rate of your transducer is referenced to certain ÒstandardÓ
conditions of temperature and pressure. Unless otherwise specified in
your order, these standard conditions are 21°C (70°F) and 760 mm of
mercury (1 atmosphere). If you wish to convert to other ÒstandardÓ
conditions or to find the ÒactualÓ conditions in the pipe where your in-
strument is installed, use the following relationship:
P
1
T
2
Q
2
= Q
1
(1)
P
2
T
1
( )
1
= The standard conditions under which your instrument
was calibrated,
( )
2
= The new standard conditions or the actual temperature
and pressure conditions in the pipe,
Q
1
= The gas mass flow rate referenced to the calibrated standard
conditions (sccm or slm),
Q
2
= The gas mass flow rate referenced to the new standard or
actual conditions (sccm or slmÑÒSÓ means Òstandard,Ó
accm or almÑÒAÓ means ÒactualÓ),
P = Absolute pressure (kg/cm
2
or psia), and
T = Absolute temperature (°K or °R) (°K = °C + 273, °R = °F + 460).
Example 1: Changing ÒStandardÓ Conditions
If your transducer has a flow rate reading of 10.00 slm and was calibrated
at standard conditions of 70°F (21°C) and 1 atmosphere (14.7 psia), and if
you wish to convert this reading to standard conditions of 32°F (0°C) and
1 atmosphere, then you would use Equation (1) as follows:
14.7 460 + 32
Q
2
= (10.0) = 9.28 slm
14.7 460 + 70
The flow rate referenced to 0°C will be approximately 7% lower than
when referenced to standard conditions of 21°C.
Example 2: Finding the ÒActualÓ Flow Rate
If the flow rate and calibrated standard conditions are as given in
Example 1 and you wish to find the actual flow rate at 100°F and 30
psig, then you would use Equation (1) as follows:
14.7 460 + 100
Q
2
= (10.00) = 3.47 slm
14.7 + 30 460 + 70