PN 305892901, Rev S
Path 2 goes directly through a capillary tube, and on to a three-way sole-
noid valve (SV2).
Paths 3 and 4 branch after the sample gas is passed through a Dryer. The
fourth ow path contains a small moisture permeation tube. Thus,
- a portion of the ow through the analyzer is a bypass,
- a portion of the ow is passed directly to the QCM Sensor assembly
(the sample leg),
- the third portion is dried before passing to the QCM Sensor (the Dry-
Reference leg), and
- the fourth ow path dries the gas and adds a controlled amount of
water vapor to the stream (the “Moisture Generator” leg).
Solenoid Valves
The three-way solenoid valves (SV2, SV3, SV4) are used to select the gas
stream that is passed through the sensor; the remaining two (2) streams are
passed to the vent. During normal operation of the 3050-RM, the analyzer
continuously cycles between the Sample- and Dry-Reference gas streams. This
switching action modulates the water vapor concentration to which the sensor
is exposed. As such, the resonant frequency of the sensor crystal is modulated,
decreasing as the sensor is exposed to the water vapor in the sample stream,
and increasing as the sensor is exposed to the Dry-Reference gas. The role of
the permeation device (Moisture Generator) is to provide an onboard means
of checking the performance of the QCM Sensor. In the “Generator Mode”, the
QCM Sensor is alternately exposed to the gas stream from the Moisture Gen-
erator and the Dry-Reference stream.
Overview | 1-7
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