8
Sensitivity to Refrigerants
The system is sensitive in varying amounts
to all of the halogen-based refrigerants,
those containing molecules of fluorine,
chlorine or both. As part of the initial setup,
the specific refrigerant to be monitored is
entered into the system. The control
electronics compensates for the differing
sensitivities, resulting in a true ppm reading
for the refrigerant specified.
Factory Calibration
The IR-SNIF-MCD is calibrated at the
factory prior to shipment. The system
maintains accuracy through automatic
rezeroing.
Periodically,
the
system
switches to the fresh air inlet, and
reestablishes a reference signal to which it
compares sample air. This process
eliminates the potential variations caused
by changes that develop in electronics as
components age. If a change in infrared
energy or detection of the infrared energy
develops, that change will be first measured
in the reference signal, then also in the
sample. The ppm level is based on the
ratio of the sample to the reference. This
ratio eliminates the effect of any variations,
and eliminates the need to periodically
calibrate a monitor in the field.
PPM vs. Leak Rate
The relationship between the actual amount
of product lost and the resulting ppm level
refrigerant in the air is complex. There is
no direct relationship between the amount
of refrigerant leaking and the concentration
being measured. The size of the room, the
location of the pick up point, the location of
the leak and airflow in the room will all
affect the actual concentration at the inlet.
However, by judicious location of the inlets
(see installation section) and maintaining
the alarm set points at a level not too far
above ambient, leaks should be detected
substantially before they otherwise would
be noticed. See Appendix B for a detailed
discussion of room volume considerations.
This appendix will help to provide a
correlation between pounds of refrigerant
lost over a given period to the ppm level
measured. This correlation can be
developed for a specific application.
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