Michell Instruments Promet I.S., User Manual

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Promet I.S. User’s Manual
Michell Instruments 3
INTRODUCTION
1.3 Theory of Operation
The reliable and robust sensor design is fundamental to achieving accurate measurement
of moisture in process over a long period of time. Proprietary thick- and thin- fi lm
techniques are applied in the Michell Ceramic Moisture Sensor. The inert materials of
the sensor have a high resistance to aggressive media while the inherent strength of
the sensor and the thermal bonded connections to the active device ensures reliable
operation.
Permeable Gold film
Hygroscopic Mono-layer
Base Electrode
Ceramic Substrate
g
g
g
g
Figure 2 Structure of the Michell Ceramic Moisture Sensor
The ceramic sensor responds to the partial pressure of water vapor in the gas being
measured, which is directly related to the dew-point temperature.
Calibration is certi fi ed traceable to NPL (UK) and NIST (USA) through the use of dew-
point transfer standards.
The fi rmware of the Promet I.S. incorporates dew point/pressure to moisture content
conversion data for ideal gas and natural gas. The calculation for natural gas uses either
the long established IGT research Bulletin No.8 or the more recently published ISO
18453, depending on the customer’s preference.