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CALIBRATION
The transmitter features a simple snap-mount sensor pcb that is pre-calibrated. This means that the entire
sensor pcb can simply be replaced with a new calibrated pcb if desired without having to remove the
enclosure. This sensor swap requires no tools and can be completed in seconds. Simply disconnect the
device wiring, remove the old sensor pcb, snap in the new pcb and reconnect the device power. There is
no need to make any adjustments or apply gas to the transmitter using the sensor swap method.
The device may also be calibrated or verified with CO gas if required. This requires a field calibration kit
consisting of a bottle of gas (250 ppm CO in air for example), a tank pressure regulator with flow restrictor
and the necessary tubing with a calibration cap to cover to the sensor. Calibration can be done at 20-27 C.
Verification with gas can be done without removing the device cover. Simply apply gas using the calibration
cap attached directly to the port on the cover as shown in Figure 6 and monitor the output signal.
The device cover must be removed to perform an actual calibration. In this case, the gas calibration cap
attaches to the sensor fixture inside the enclosure as shown in Figure 7. The sensor must be continuously
powered for at least 1/2 hour prior to calibration. Calibrate the sensor first in clean air with no CO gas
present. Simply adjust the ZERO pot on the sensor board until a 0 Vdc output is obtained. For this case,
adjust the output slightly above 0 Vdc and then slowly reduce the output signal to 0 Vdc. The output signal
may be monitored with a voltmeter connected to the OUTPUT and COMMON terminals.
Then attach the gas supply. Turn the regulator on/off knob fully off and attach it to the 250 ppm gas bottle
and firmly tighten it by hand. Moisten the sponge and squeeze out any excess water. Place the sponge
in the cap so that it will not touch the sensor but does not plug the hole in the side of the cap. Attach the
cap to the fixture over the sensor. Slowly turn the valve knob on the regulator to let the gas begin flowing.
The regulator will restrict the flow rate to the specified 200 ml/min and the sponge will ensure the gas is
in the right humidity range. Wait for 5 minutes and then adjust the SPAN pot on the sensor board until the
output reads 250 ppm. For the 0-300 ppm device span, 250 ppm would equal 8.33 Vdc. Close the valve on
the tank and take the cap off from the sensor. Calibration is complete.
If the gas cap is too loose on the fixtures, simply place a wrap of electrical tape around the cap to tighten it.
Figure 6
Figure 7
IN-GE-CMD5B1000XXX-002
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