EX-5155
ENMET
Addendum: Ammonia Calibration
Calibration Procedure for EX-5155-MOSAmmonia
Manual Release Date –
November 26,
2018
Manual Part No. –
80003-098
P a g e
|
20
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 and therefore the standard regulator assembly cannot be used.
ENMET
has developed a special calibration adapter for ammonia that allows the calibration gas to be humidified without passing
through water. The part number of this adapter is 03700-005. Instead of the calibration gas being flown through the water the
calibration gas is passed over the water. The calibration gas picks up enough humidity to properly calibrate the sensor, but not enough
to absorb all the ammonia calibration gas
For 0 – 500 ppm range ammonia transmitters, the proper calibration point is 200 ppm. The calibration gas cylinder is 300 ppm NH3 in
air. While flowing the 300 ppm ammonia through the calibration adapter humidifier assembly 100 ppm of the ammonia is absorbed in
the water with the remaining 200 ppm reaching the sensor.
Unscrew the bowl from the humidifier and place enough water into the bowl to reach the bottom edge of the tube.
DO NOT let the water cover the tube. The tube should not penetrate the water. Connect the calibration adaptor to the cylinder
of ammonia. Place the unit into calibration mode (reference Section 5.0) and perform a ZERO calibration. DO NOT enter the
span sequence.
•
Open the valve on the calibration adapter regulator.
•
Verify that the gas sample is passing over the water by looking for gentle ripples on the water surface. There should
not be bubbling. Flow rate is preset by the regulator and needs no adjustment.
•
Connect the calibration cup to the sensor and allow the gas to flow for 3 minutes.
•
At the end of the 3 minutes tap the SELECT switch on the
EX-5155-MOS
to start the span operation. The display will
alternate between PV and a number.
•
Continue to let the calibration gas flow for an additional 1 minute then tap the SELECT switch again. This will end the
span operation and the display should read CAL OK.
•
Tap the MENU switch until EXIT appears and then tap the SELECT switch to exit the calibration menu and return the
unit to its operation mode.
The
EX-5155-MOS
Ammonia sensor requires special calibration techniques that are not common with other gases.
Notes:
