About this task
The CO sensor features a simple snap-mount sensor pre-calibrated PCB. You can replace the entire sensor PCB with a new calibrated PCB without the removal of the enclosure. This sensor swap requires no tools and you can complete it in seconds. 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 device when you use the sensor swap method.
If necessary, calibrate the device or verify with CO gas. This requires a field calibration kit that consists of a bottle of gas, for example, 250 ppm CO in air, a tank pressure regulator with flow restrictor, and the necessary tubing with a calibration cap to cover the sensor. You can calibrate at 68°F to 81°F (20°C to 27°C).
Verify with gas without removing the device cover. Use the calibration cap attached directly to the port on the cover to apply gas and monitor the output value. See Figure 1. Remove the device cover to perform an actual calibration. In this case, the gas calibration cap attaches to the sensor fixture inside the enclosure. See Figure 2.
Continuously power the sensor for at least 30 min prior to calibration. Calibrate the sensor first in clean air with no CO gas present. To calibrate the sensor, complete the following steps:
- Adjust the ZERO pot on the sensor board until you obtain a 0 ppm output.
- 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 flow. 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 min and adjust the SPAN pot on the sensor board until the output value reads 250 ppm.
- Close the valve on the tank and take the cap off from the sensor. This completes calibration.
- If the gas cap is too loose on the fixtures, wrap electrical tape around the cap to tighten it.