4 System Components
4.1 AcuDew
The AcuDew Dewpoint Transmitter is a 2 wire, 4 to 20mA loop powered device,
used for continuous measurement of moisture in process gases, including the
most common application, compressed air. The AcuDew transmitter is configured
to output a 4 to 20mA linear signal for the following moisture units:
• Dewpoint temperature, °C
• Dewpoint temperature, °F
• Parts water vapour per million in a gas (PPMV)
• Parts water vapour per billion in a gas (PPBV)
In normal operation, the transmitter will produce a 4 to 20mA signal, which is
proportional to the level of moisture in the gas being monitored. The moisture
reading is sampled and updated once per second. The AcuDew has 3020 distinct
steps over the 4 to 20mA range corresponding to a resolution of 0.005mA.
The sensing element is a robust sensor designed for process applications with high
sensitivity and excellent speed of response. Each sensor/transmitter is calibrated
against standards that are traceable to the NPL.
The “state-of-the-art” microprocessor circuitry of the AcuDew transmitter drives
its high resolution and provides advanced self-diagnostics. The transmitter stores
the calibration data onboard and provides a linear 4 to 20mA signal over the
moisture range, making the AcuDew truly “plug-and-play”.
The transmitter also incorporates the unique AutoCal function, only applicable
due to the highly sophisticated sensor design. Because the sensor is so linear in
its response to moisture and due to a “capped 4 to 20mA” sensor output, the
transmitter can be accurately recalibrated by exposing its sensing element to
typical ambient air. The AutoCal feature of the AcuDew allows users to easily
verify/correct changes in the sensor response in between normal NPL traceable
recalibrations, providing improved performance over other moisture sensors and
technologies. If a calibration gas of known moisture content is available, this can
be used instead of ambient air when performing an AutoCal.
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