COSA Xentaur Xentaur XDT - Manual (Page 29)

XDT User’s Manual
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displaying the calculations and then will display END for a few seconds, after which the instru-
ment will automatically go into measuring mode. The sensor calibration is completed. (The
display may flash SAT, indicating that the sensor has super-saturated. As soon as the sensor is
exposed to an atmosphere with a dewpoint lower than the saturation dewpoint, the display will
indicate the dewpoint measured by the sensor.) The display may show alternating SEN and 2LO
as an indication that the measured capacitance is too low to be from a saturated sensor, in this
case make sure that the sensor is properly plugged in, and repeat the calibration procedure.
7. Install the sensor in the sample cell or adapter fitting or put it back into the packaging con-
tainer for later use.
The instrument will retain the calibration even if the power is turned off.
Under certain conditions, an over (super) saturated sensor may need to be completely dried out
before a calibration is performed. Symptoms of these conditions are a sensor that will not go
through the SpanCheck™ function to the END display, or a sensor that will not dry down after cal-
ibration. To dry, install sensor in either a known dry gas stream i.e. instrument quality air or dry
nitrogen, or place sensor in a dry can or bottle of desiccant and seal the container from outside air
(the shipping container is designed for this purpose). After a minimum dry out period of 24 hours,
proceed with the calibration procedure of your choice.
SpanCheck™ calibrates sensors by using micro climates. Please contact your representative if
you have any questions about how to create such micro climates.
A perfectly acceptable and accurate for calibration micro-climate may be created for the XTR100
and XTR65 sensors by cupping the sensor in the palm of one’s hand during the SpanCheck™ pro-
cedure. Remember that the micro-climate does not have to be accurate, it just has to be higher
than the designed saturation level. The dewpoint of the micro-climate within the fingers is usually
higher than the dewpoint of the room air and probably well above the +20°C upper range of the
sensor. On a dry day, one may need to exhale in the hand before cupping the sensor to guarantee a
high dewpoint. The sensor should be warmed up close to body temperature before performing this
procedure. Care must be taken that the sensor temperature is not below the temperature of the
hand, as in such case condensation could occur and super saturate the sensor. For the same reason,
avoid exhaling directly onto the sensor.
3.4.4.3.2 Single Point Self Calibration, manual or scheduled
The instrument is calibrated at the factory with the sensor it is shipped with and does not need to
be re-calibrated prior to installation.
Single point calibrations should be performed whenever the measurement is in question, or on a
scheduled basis depending on the application. Consult with your representative to establish crite-
ria for specific applications.
The single point calibration is performed on the premise that the sensor is exposed to a gas with a
known dewpoint for a time sufficient to equilibrate. Then the sensor output is measured, and the
calibration curve is adjusted to provide measurement computations which correspond to the
known dewpoint. Measurements over the full sensor range are linearly adjusted to this known
point.
The single point calibration provided by this instrument may be performed manually, or (when a
sample system is ordered equipped with an electrically actuated switchover valve) unattended on