ENMET EX-5150-MOS - Manual (Page 17)

EX-5150-MOS ENMET Corporation
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Addendum: Ammonia Calibration
Calibration Procedure for EX-5150-MOS Ammonia
The EX-5150-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 and
TAP the
S ELECT switch to make the display read the humidified output +/- 20 ppm.
Fresh clean water must be used for each calibration.
Notes: