Ametek 3050-RM, User Manual

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Overview
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1-5
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Path 2 goes directly through a capillary tube, and on to a three-way
solenoid valve (SV2).

Paths 3 and 4 branch after the sample gas is passed through a dryer.
The fourth flowpath contains a small moisture permeation tube. Thus,
- a portion of the flow through the analyzer is a bypass,
- a portion of the flow is passed directly to the QCM sensor assem-
bly (the sample leg),
- the third portion is dried before passing to the QCM sensor (the
dry reference leg), and
- the fourth flow 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 streams are
passed to the vent. In 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 crys-
tal 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 on-board 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 generator and the dry reference stream.