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boxes for you to “check” with an “X,” and these allow for multiple items in a list to be selected.
In all cases of editing, you can save or undo your choice.
9.3.2 Calibration
Use this menu to perform a bump test or zero or span calibration for one or more sensors, and change the gas
concentration value used in bump tests and span calibration, as well as choose which sensors will be calibrated at the
same time.
9.3.3 Bias & Equilibration For Liquid O
2
And Other Biased Sensors
Some electrochemical sensors (NO, NH
3
, Liquid O
2
) require a bias voltage to detect the gas,
while most do not. Unbiased sensors may be shipped with a shorting pin across the electrodes to
avoid an accidental bias. The pin should be removed before installation. Biased sensors require
an equilibration time (also known as warm-up time) of at least 6 hours, and sometimes more,
after installation for the baseline to become stable enough to calibrate the sensor. Unbiased
sensors require at least 10 minutes to stabilize. Once installed, any sensor bias stays on, even
when the meter is off. Therefore, even biased sensors are ready for immediate use when the
instrument is turned on again, and the equilibration time is needed only when first installed or if
the battery becomes completely drained. The SensorRAE 4R+ can be used to maintain bias on
NO and other biased sensors, so long equilibration times can be avoided when installing such
sensors into a multi-gas instrument.
CAUTION
If an instrument is calibrated directly after sensor installation (no equilibration time, no use of
SensorRAE 4R+), readings will be seen to decrease until the sensor’s bias is is stable. Also, this
may may trigger a low alarm, even if calibration passes.
Refer to RAE Systems Technical Note TN-114 for a list of biased sensors.
9.3.3.1
Fresh Air
This procedure determines the zero point of the sensor calibration curve for all the sensors that require a
zero calibration. For the oxygen sensor, Fresh Air calibration sets the point equal to the concentration of
oxygen in ambient air (approximately 20.9% volume).
Note:
Fresh air calibration is performed on all enabled gas sensors at the same time.
To perform Fresh Air calibration on multiple sensors:
1.
If using dry air, install the calibration adapter and connect it to a source of dry air. Otherwise do not
use calibration adapter to perform fresh air calibration.
2.
At the Calibration Menu, select “Fresh Air.” Press [Y/+] once to enter the fresh air calibration sub-
menu.
3.
Start the flow of dry air, if used.
4.
Press [Y/+] to start fresh air calibration.
