User guide

4 - 2
PN 074-566-P1B
Composer Elite Operating Manual
The correct (user set) Reference Zero is retained until a new Reference Zero is
established, the Setpoint Temperature is changed or new carrier gas
parameters are entered.
NOTE: STEADY and AT TEMP must be visible when completing the Calibration
process. This indicates the measurement conditions are stable and a
relative equilibrium has been reached. It sometimes takes many minutes
for the light (low molecular weight) carrier gas to clean the Resonant
Chamber of any residual Precursor or other heavy gases. Remember that
some gases may also absorb on the Resonant Chamber’s walls and are
slowly released, further extending the time to reach pure carrier gas as
indicated by stable frequency.
CAUTION
Setting Zero Reference before the Resonant Chamber is
completely purged of precursor gas will result in an
offset and scaling error in the measured concentration.
See section 4.1.10 on page 4-8.
4.1.3 How is Performance Affected if I Use the
Factory (Reference) Zero Value?
While it is most accurate to reset Reference Zero daily, excellent results can be
obtained for many processes by using the Factory Zero value for Reference Zero.
While the exact loss of reproducibility is hard to predict, it is reasonable that it will
be about two to four times worse than the specified value when monitored over
extended periods of time. This may be acceptable, and convenient, for the process.
Alternating between the Factory Zero and carefully setting the Reference Zero
occasionally will not be productive. It would be better to extend the interval between
reestablishing the Reference Zero than to alternate. An example of long term
stability is shown in section 4.1.9 on page 4-7.