Rae AutoRAE 2, User Manual

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calibrate the most cross-sensitive sensor first, followed by the least cross-sensitive. Wait
for both sensors to recover to zero, and then expose both to gas again with most cross
sensitive first and least cross sensitive second.
For example, 50 ppm of NH
3
produces 0 ppm response on a Cl
2
(less cross-sensitive)
sensor and 1 ppm of Cl
2
produces about -0.5 ppm of response on a NH
3
(more cross-
sensitive) sensor. So calibrate the NH
3
sensor first with 50 ppm of NH
3
. This should have
no effect on the Cl
2
sensor. Then calibrate the Cl
2
sensor with 10 ppm Cl
2
. This will send
the NH
3
sensor negative for some period of time.
After calibrating the Cl
2
sensor, return the instrument to clean air and wait until the most
cross-sensitive sensor (NH
3
) fully recovers and/or stabilizes (if it stabilizes to a number
other than zero, then re-zero the instrument).
After both sensors return to zero, expose both to calibration gas in the same order (NH
3
first, and then Cl
2
.) Note the sensor response. If both sensors are within 10% of the value
shown on the gas cylinder, then the calibration of the cross-sensitive sensors was
successful.
This same logic applies to the order of performing a bump test on an instrument that has
cross-sensitive sensors. For more information on cross-sensitivities for select sensors,
consult RAE Systems Technical Note TN-114.