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Moisture Sensor
Quartz Crystal Microbalance (QCM)
The 3050-AMS Analyzer uses a QCM Sensor to measure water vapor concentra-
tion. This is a piezoelectric device that is capable of extremely sensitive mass
measurement. To make the QCM sensitive to water vapor the surface is coated
with a thin film of hygroscopic material. When gas flows through the Sensor,
the coating absorbs or desorbs moisture, changing the natural resonance
frequency of the crystal.
Gas Measurement Cycle
The gas measurement cycle is divided into two periods.
1-4 | 3050-AMS Moisture Analyzer
During the first period of the cycle, dry Reference gas flows through the
Sensor assembly and the frequency is recorded.
During the second period of the cycle, Sample gas flows through the Sen-
sor and a second measurement of the Sensor frequency is recorded.
The difference between these two frequency measurements is known as
the delta frequency (∆ƒ). The ∆ƒ value is a function of the moisture con-
centration in the Sample gas.
PN 305804902, Rev A
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