Solenoid Valves - Ametek 5800 User Manual

you reduce the time required to equilibrate all portions of the sample
system that exist upstream of the bypass valve. A capillary tube,
located immediately downstream of SV1 (the coil shape in Figure 1-2),
limits the flow rate to approximately 1 standard liter per minute (the
exact value of the bypass flow is a function of the inlet pressure to the
analyzer).
The remaining three flow paths are supplied with sample gas by a pro-
portional solenoid valve (PSV), which is used to regulate the flow of gas
through the analyzer. Downstream of the PSV, the remaining three flow
paths separate.
Path 2 goes directly through a capillary tube, and on to a three-way
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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. The two-way solenoid valve (SV5) is used to isolate
the dryer from moisture when power is removed from the analyzer. In
normal operation of the 5830, the analyzer continuously cycles between
the sample- and dry-reference gas streams. This switching action modu-
lates the water vapor concentration to which the sensor is exposed. As
such, the resonant frequency of the sensor crystal is modulated, decreas-
ing 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.
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