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Chapter 3 _______________________________________________________ Functional Description
VAISALA_________________________________________________________________________ 5
CHAPTER 3
FUNCTIONAL DESCRIPTION
This chapter describes the advanced functionality of Dewpoint
Transmitter DMT142, including the auto-calibration, sensor purge and
sensor warming functions.
Advanced DRYCAP
®
Technology
Dewpoint Transmitter DMT142 utilizes an advanced, patented
measurement technology to ensure accurate measurement with
excellent long term stability. This results in very low maintenance
requirements for the transmitter. The lasting performance is achieved
with microprocessor technology and software that automatically
performs self-diagnostic functions in addition to the normal dewpoint
measurement. The self-diagnostic procedures that are conducted are
called auto-calibration, sensor purge and sensor warming.
Auto-Calibration
The auto-calibration feature of the DMT142 transmitter is an
automatic procedure which greatly reduces the possible drift in the dry
end of the dewpoint measurement. It is performed at one hour
intervals, and when the power is switched on. During auto-calibration
the sensor is warmed for a short period (< 1 min) and the sensor
capacitance values are evaluated at the elevated temperature. The
possible dry end drift is then corrected to correspond to the calibrated
values. During the auto-calibration the transmitter outputs the T
d
value
prior to the procedure.