About this task
The NO2 transmitter features a simple snap-mount pre-calibrated sensor 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 transmitter using the sensor swap method.
If necessary, calibrate the device or verify with NO2 gas. This requires a field calibration kit that consists of a bottle of gas, for example, 10 ppm NO2 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).
You can verify with gas without the removal of 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.
For local display, place an ammeter in series of the output. Disconnect the signal wire from the OUT terminal of the NO2 sensor. Connect the positive lead of the ammeter to the OUT terminal of the NO2 sensor and connect the COM lead of the ammeter to the removed signal wire. Set ammeter to read a 20 mA signal.
Continuously power the sensor for at least 30 min prior to calibration. To calibrate the sensor, complete the following steps:
- Calibrate the sensor first in clean air with no NO2 gas present. Adjust the ZERO pot on the sensor board until you obtain a 4 mA output.
- Attach the gas supply.
- Turn the regulator on/off knob fully off and attach it to the 10 ppm NO2 gas bottle and firmly tighten it by hand.
- Attach the cap to the fixture over the sensor.
- Slowly turn the valve knob on the regulator to let the gas flow.
Calibrate the sensor either by applying SPAN gas with a flow rate of 0.5 L to 1
L per min or wait 2 min and adjust the SPAN pot on the sensor board until you
obtain a 20 mA output.
Note: The SPAN gas does not have to be the full scale concentration, but could be a fraction of this. A half-scaled concentration of 5 ppm provides a 12 mA signal.
- 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.