COSA Xentaur Xentaur XDT - Manual (Page 32)

Section 3: Instrument
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indicating that Self Cal Stabilization is being checked and currently the instrument is measur-
ing -41.5°C. When the measured dewpoint is stable within 0.5°C for 3 minutes the instrument
will record the new single point self calibration values. Note that the program will spend at
least 3 minutes on this stage of the calibration.
• The electrically actuated switchover valve will be deactivated thus introducing the sample gas
to the sensor, and the dewpoint will be monitored for stability. The display will show S.C./
FIN/-42 indicating that self calibration has finished and it is measuring a dewpoint of -42°C.
When the measured dewpoint is stable within 0.5°C for 3 minutes the instrument will
“unfreeze” the analog output and relays and go to the display dewpoint mode.
• The instrument will display the measurement using the newly acquired calibration values.
The instrument computes the dewpoint from the measured capacitance of the sensor. The
sequence of computations is as follows:
•
The capacitance is converted to percent of full scale (-100°C to +20°C dp), using the low dB,
low dew, and saturated dB when performing SpanCheck values.
• Cal Adj is applied to correct the mid point of the curve.
• If enabled, the multi-point calibration table is applied to further correct the transfer function.
• If enabled, the single point calibration is applied to fine tune the transfer function.
• The corrected percent of full scale is converted to dewpoint.
3.4.4.4 Viewing Serial Number Mode
In this mode the user can view the instrument serial number. The display shows the serial number
by alternately displaying XSN and the number. If the number is larger than 1999 then it is dis-
played in 2 parts, first part is the thousands signified by the x10
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legend in the upper right corner
of the display and the second part is the units. For example serial number 12345 will be shown as:
Pressing the UP and DOWN buttons simultaneously resets the instrument, this is useful in instal-
lations where power can not be turned on and off easily. Pressing the Pressure Correct button will
cause the instrument to enter the setup state.
Pressing the MODE button, returns the unit to the Viewing Dewpoint Mode.
3.4.5 SetUp State
To enter the Setup State power-up the unit (or reset it from the serial number Mode), and hold the
MODE key pressed while the unit is initializing. Refer to Appendix B for a flow diagram of the
SetUp State.
The setup state provides eleven capabilities, each one controlled from its own mode. Depressing
the MODE button navigates through the modes in the following order: nSelect Alternate Display
Units oSelect Sensor Type pSet Measured Attenuation of Sensor at a Low Dewpoint qSet the
Low Dewpoint at which the Attenuation was measured rSet the Calibration Mid-range Adjust
sAnalog Output select 4/20mA or 0/24mA tPerform a Test and Verification of the Analog Out-
put uSet dewpoint corresponding to low end of Analog Output vSet dewpoint corresponding to
x10 3
12 345 XSN