Panametrics DewPro MMR30, Installation & Operation Manual

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DewPro® MMR30 Installation & Operation Manual 3
Chapter 1. General System Information
1.3 Theory of Operation
1.3.1 4 to 20 mA Loop
The DewPro MMR30 microprocessor controlled electronics operate with a DC voltage supply from 12 to 28 VDC. At the
nominal 24 VDC supply, the maximum loop resistance is 600 Ohm. The signal is represented by the 4 to 20 mA loop
current and is directly proportional to the dewpoint range in °C or °F. In the standard range, 4 mA corresponds to
-15°C (+ 5°F) and 20 mA to +85°C (+185°F) dew point temperature.
1.3.2 Bypass
In dryer applications, the moisture sensor performs best when mounted in a bypass. The built-in bypass of the
DewPro eliminates costly hardware associated with traditional sampling methods. The DewPro installs easily into the
process with its G ½ or ½” NPT-M threaded connection.
1.3.3 Polymer Sensor
The sensing element in the MMR30 is a silicon-based polymer that uses the capacitance principle for the moisture
measurement. The IC chip includes the moisture sensor and appropriate integrated circuitry. A platinum RTD
temperature sensor is built in to provide temperature compensation for maximum accuracy. The sensor element is
protected from condensation using a hydrophobic sintered filter.
1.3.4 Calibration
Each DewPro is factory calibrated against precise NIST certified moisture references and has an accuracy of ±1°C
dew point for dew points above 0°C. Field calibration is possible with the use of a moisture generator. Consult the
factory for details.