PN 305892901, Rev S
Moisture Sensor
Quartz Crystal Microbalance (QCM)
The 3050-RM Analyzer uses a quartz crystal microbalance sensor to measure
water vapor concentration. 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 lm of hygroscopic material. When gas
ows 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 (2) periods.
During the rst period of the cycle, dry Reference gas ows through the
Sensor assembly and the frequency is recorded.
During the second period of the cycle, Sample gas ows through the Sen-
sor and a second measurement of the Sensor frequency is recorded.
The dierence between these two (2) frequency measurements is known
as the delta frequency (∆ƒ). The ∆ƒ value is a function of the moisture con-
centration in the Sample gas.
1-4 | 3050-RM Moisture Analyzer
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