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XDT User’s Manual
26
CAUTION:
2), 3), 4) and 5) are set at the factory and need only be modified when a sensor is changed.
2. Selecting the sensor type: In this mode the user can select the software matching the type of
sensor installed in the instrument: XT1 : XTR-100 (-100°C to +20°C);
XT6 : XTR-65 (-65°C to +20°C);
DB : show impedance of any sensor, disable
Open and Short error massages.
3&4Adjusting low end sensor attenuation and dewpoint: These modes are used to enter a data
pair representing a low dewpoint and the sensor attenuation measured at this low dewpoint.
(see Sensor Theory of Operation appendix F). This data pair should not be modified unless the
sensor is replaced (refer to procedures for replacing a sensor in appendix L). The sensor ship-
ping container is labeled with the proper values.
5. Calibration Adjustment: In this mode the user can enter a sensor specific Adjustment Value
to improve the instruments’ accuracy in the range of -50°C to -10°C, this adjustment has very
little or no effect outside this range. The Calibration Adjustment Value is printed on the ship-
ping container supplied with the sensor, or may be derived if the sensor can be exposed to a
known reference.
Deriving an Adjustment Value: If the adjustment value for your sensor is not known, contact
your representative and follow the instructions below for entering known values. If the value
is not available, then it may be derived using a manual method, provided that a moisture cali-
bration facility is available.
The calibration must be done in the range of -25°C to -20°C (attempting to calibrate outside
this range may cause inaccuracies), the dewpoint must be kept stable during calibration and it
must be measured accurately by a reference instrument such as a chilled mirror. One must also
note the state of pressure compensation and turn it on or off as applicable to the reference.
The necessary steps are described below (also refer to the Set-Up State flow diagram in
Appendix B):
a. Make sure that the low attenuation and low dewpoint are correctly entered for this sensor.
b. SpanCheck™ the sensor.
c. Dry-down the sensor for at least 12 hrs.
d. Expose the sensor to the known dewpoint (-25°C to -20°C), for a sufficient time (at least 30
min.)
e. Go to the CAL/ADJ mode and press the UP button, the display will show the current value,
in the range of -1.99 to +1.99 followed by blinking horizontal lines.
f. Observe the display, if the buttons are not being pressed; the display will every few seconds
show for a short duration the dewpoint as being computed at the moment (utilizing the current
cal-adjust value in the computation).
g. Use the UP or DOWN buttons to modify the cal-adjust value and observe the alternately
displayed dewpoint. Perform this adjustment until the dewpoint matches the value shown by
the reference instrument.
h. Press the MODE button to go to the next mode, this will save the new cal-adjust value, and
it will be retained even if power is turned off.
Entering a known Adjustment Value: If the sensor is being replaced an adjustment value
should be supplied with the sensor, to enter it into the instrument: