Michell Instruments QMA401, Руководство пользователя

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QMA401 User’s Manual
Michell Instruments 45
OPERATION
At the close of this 30 second sampling period, V1 is de-energized, and V2 is energized; so
that the reference gas from the moisture generator is now routed to the sensor cell. This is
the beginning of phase 2, see Figure 28.
The calibration reference gas is measured for a further 30 seconds, until V2 is de-energized
and the cycle begins again.
The inactive sample paths are continually purged during each phase (see green flow paths
on Figures 25 and 26).
SAMPLE
IN
SAMPLE
OUT
DD
HE1 HE2
FC1 FC2 FC3
V1 V2 V3
MFC
QCH
PS
MG
Key
DD
Desiccant column
MG
Moisture generator
MFC
Mass flow controller
V1, V2, V3
Solenoid valves
QCH
Sensor cell
HE1, HE2
Heat exchanger
PS
Pressure sensor
FC1, FC2, FC3
Flow control
Figure 41 Calibration Cycle (Phase 2) - Sample Flow
The analyzer will run though a number of 'settling cycles' to ensure the internal sample
system is fully equilibrated with the calibration gas before beginning to collect calibration
data.
After the system has carried out the selected number of settling cycles, it begins the
calibration cycles. During these cycles, the difference between the calibration reference gas
and the dried gas is measured. As the moisture content of the calibration gas is known, the
difference between this and the measured value is equal to the error in the system.
The QMA401 stores this measured calibration value and automatically compensates
subsequent sample readings for any offset that may have occurred to the factory calibration
curve.