DH Instruments COMPASS FOR MOLBOX, User Manual

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COMPASS

for molbox™ User’s Manual
© 1998-2003 DH Instruments, Inc .
Page 194
VARIABLE DESCRIPTION
DUT
U
Calculated DUT measurement uncertainty expressed as a value in
DUT flow units, using a coverage factor of 2. The value is reported
as %DUTFS by dividing by the DUT’s span and multiplying by 100.
EstErr
S
Standard estimate of error for a first order linear regression. This
value combines linearity, hysteresis and repeatability. The value is
the standard deviation of the error from a linear fit.
E
resolution
Specified DUT resolution. This value is determined by the resolution
selection in the DUT Definition.
U
std
Uncertainty of the reference as specified in the reference hardware
definition. The value is converted to the DUT’s flow unit of measure
for the calculation.
19.12 FLOW UNIT CONVERSIONS
COMPASS performs all internal flow conversion to and from kg/s. There are three types of unit
conversion: mass to mass, mass to volume, and mass to perfect. Each type of conversion may require a
scaling factor to convert time, volume and mass dimensions as required by the unit. In other cases, gas
specific properties are required for the conversion. A mass to mass conversion requires a simple scaling
factor. Mass to volume conversions always convert to sccm (or ccm) at the required pressure and
temperature, then a scaling factor is used to convert to the final unit. For example, sccm to slm
conversions require multiplication by 0.001. Mass to perfect unit conversions first convert to mol/s then to
pccm. A scaling factor is applied as need to convert from pccm to other perfect units. Use
[Tools] , [Unit
Converter] to determine flow unit conversions in various gases.
Table 64 describes the basic equations to perform each conversion.