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11.3 Zero/Fresh Air Calibration
This operation sets the zero point of the sensor calibration curve for clean air. It should be performed
before other calibrations.
IMPORTANT!
Even though most toxic gas sensors can be zeroed in fresh air, sensors such as the CO
2
and the parts-per-
billion PID sensor for volatile organic compounds (VOCs) should not be zeroed in fresh air. Both CO
2
gas and
VOCs are normally present in ambient air, so zeroing these sensors in ambient air will not allow for a true zero
to be set for such sensors. The CO
2
sensor should be zeroed in 99.9% nitrogen and the parts-per-billion PID
sensor should be zeroed with ambient air using a charcoal filter or a VOC zeroing tube.
Note:
If you use a zero air or other gas cylinder, you must use the MultiRAE Calibration Adapter. A
calibration adapter is not necessary for calibration in fresh air.
11.3.1 Zero Calibration For A CO2 Sensor
IMPORTANT!
If your MultiRAE is equipped with a CO
2
sensor, it must be zero calibrated using 100%
Nitrogen (N
2
), which is inert, instead of fresh air or zero air.
11.3.2 Zero Calibration For Parts-Per-Billion (ppb) Sensor
IMPORTANT!
The parts-per-billion PID sensor for volatile organic compounds (VOCs) should not be
zeroed in fresh air. VOCs are normally present in ambient air, so zeroing the sensor in ambient air will
not allow for a true zero to be set. The parts-per-billion PID sensor should be zeroed with ambient air
using a charcoal filter or a VOC zeroing tube.
11.3.3 Fresh Air Calibration
This procedure determines zero points of most sensors. The MultiRAE should be zero-calibrated in clean
air with 20.9% oxygen or with a cylinder of clean zero air.
At the Calibration menu, select “Fresh Air” by pressing [Y/+] once to enter fresh air calibration.
After a timer countdown, the zero calibration is done. The LCD displays the sensor names and tells you
whether each calibration passed or failed, followed by the sensor readings.
Note:
You can abort the calibration at any time during the countdown by pressing [N/-].
