ENMET EX-5155 - Manual (Page 17)

EX-5155-MOS ENMET Corporation
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Addendum: Ammonia Calibration
Calibration Procedure for EX-5155-MOS Ammonia
The EX-5155-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 developed 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 0 – 500 ppm range Ammonia transmitters, the proper calibration gas cylinder is 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.
Place the EX-5155-MOS unit into calibration mode reference Section 5.0. Following the Zero Calibration
the EX-5155-MOS will be at SPAN.
Do Not start the Span sequence.
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 enter the Span operation.
The display will alternate between calibration gas and concentration.
Tap the S ELECT switch again to exit Span operation.
The display will read CAL OK if the calibration was successful.
Fresh clean water must be used for each calibration.
Notes: