Thermo Scientific Sarasota SG901, User Manual

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Calibration
Adjustment
5-2
Sarasota SG901 User Guide Thermo Fisher Scientific
From line density, we calculate density at the chosen reference conditions.
Where density at reference conditions is calculated as:
where Z and Zref are the compressibility (divergence from ideal gas
equations) at measurement and reference conditions. Z and Zref are
calculated using the Redlich Kwong equation of state which uses two
constants: Az and Bz (Sarasota HC900 and Sarasota CM200) or critical
temperature and critical pressure (Sarasota CM515). These constants can
be calculated from tables based on gas mixture, or in cases where the
mixture is hydrocarbon, from a built-in fit (Az and Bz from MW).
SG is then calculated by dividing the sample reference density by the
density of air at the same conditions.
A full set of equations is included in
Appendix E .
System adjustments should only be made after a number of samples have
been taken to establish an average error. Failure to do this or attempts to
adjust the system based on one reading or sample may actually increase the
error. To make an adjustment:
1. Ensure the pressure and temperature readings are an acceptable
accuracy.
2. Set the density correction factor (DCF) to 1 and the density offset
(Doff) to 0.
3. Take a series of samples and synchronous readings of SG. Have the
samples analyzed and calculate the average error.
Assuming the thermometry, pressure measurement, supercompressibility
calculations, and isentropic exponent are operating correctly, the
adjustment can be made using the DCF or the Doff. Either option is
acceptable, but the Doff should give better results as long as the span of the
system is relatively small.
To calculate the Doff, you will need to know the following synchronous
data: average SG error and average line density during the test.
Adjustment
Correction
Calculation
,
Zref Tref P
Z T ef Pr
m
c
× ×
× × × ρ
= ρ