ENMET EX-5000 - Manual (Page 12)

ENMET Corporation Catalytic &MOS S/T
10
Addendum: Ammonia Calibration Addendum: Ammonia Calibration
Calibration Procedure for EX-5000 MOS Ammonia
The EX-5000 MOS Ammonia sensor requires special calibration techniques that are not common with other gases.
All MOS sensors require at least 15% RH for proper operation. RH of 50% or greater is ideal for MOS sensor
calibration. The common technique for humidifying dry gas from a cylinder is to bubble it through a humidifier
assembly. However, ammonia is readily absorbed in water.
ENMET Corporation has supplied a special calibration adapter for ammonia that allows the humidifier bowl to be 1/3
full of water, but not bubble the gas sample. Instead the gas sample is passed over the water. It is still able to pick up
enough humidity to properly calibrate the sensor, but not enough to lose all of the ammonia calibration gas.
For up to 0-500 ppm range Ammonia transmitters, the proper calibration gas cylinder is approximate 300 ppm NH3 in
air. While flowing the 300 ppm ammonia through the calibration adapter humidifier assembly, approximately 200
ppm is the actual concentration going to the sensor, the difference being absorbed by the water surface. See the
cylinder for the humidified output.
Open the valve on the calibration adapter regulator, and attach the calibration cup to the sensor. Verify that the gas
sample is passing over the water by looking for gentle ripples on the water surface and not bubbling. Flow rate is
preset by the regulator and needs no adjustment. Apply the calibration gas for four minutes. At the end of four
minutes, use the magnet to adjust the – or + buttons and make the display read the humidified output +/- 20 ppm.