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Solenoid Valves
The sensor assembly is connected to both legs of the analyzer, and immedi-
ately downstream of the connection points, there are two (2) solenoid valves
(SV1 and SV2). These two solenoid valves switch the flow of the Sample and
dry Reference gases through the QCM sensor. By opening SV1 while SV2 re-
mains closed, the flow of the dry Reference gas is diverted through the sensor
allowing the flow of sample gas to continue to flow through SV1 (Figure 1-2).
By opening SV2 while SV1 is closed, the sample gas flow is diverted through
the sensor and out SV2 and the dry Reference gas continues to flow through
SV2 (Figure 1-3).
As the sensor is alternately switched between the Sample and Reference gas
streams, the 5920 microcontroller monitors the frequency changes in the QCM
sensor. The difference in frequency measured between the two gas streams is
then used to calculate the water vapor concentration of the sample gas enter-
ing the analyzer.
Sample Gas IN
DV1
DV2
DV3
Purifier
OPEN
CLOSED.
D V
= Diaphragm Valve
S V
= Solenoid Valve
MFM = Mass Flow Meter
Figure 1-3.
Flow during Sample cycle.
Zeroing the Analyzer
The zero process is used to correct any offsets in the sample system. By com-
paring the two zero readings (Reference and sample) with the internally gener-
ated "zero" gas, any offset can be zeroed out. This is done by measuring the
zero offset frequency and storing it in memory. This offset is then subtracted
from ∆ ƒ before the sample moisture concentration is calculated.
PN 592047901 Rev YC
Gas A
Pressure
Sample Gas
Regulator
SPLIT
Gas B
MFM
Sample Gas Flow/Path
Reference Gas Flow/Path
SV3
DV4
Purifier
SV1
Sensor
SV2
|
Overview
1-7
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