ENMET ISA-44-RAL-OD - Manual (Page 16)

ENMET Corporation ISA-44RAL-OD / ISA-44RAH-OD
12
5.3.2 Air Quality and Pressure Adjustments
For the O XYGEN D ETECTION C HANNEL : Atmospheric conditions and conditions inside your air compressor are
constantly changing. In order to maintain a clean oxygen reading of 20.9% oxygen the oxygen Gain Potentiometer must
be adjusted periodically. Check the oxygen meter daily. If it continually shows a percentage other than 20.9% for 15
minutes in the presence of compressor air, double check that the compressor air is really clean by exposing the cell to
bottled clean air from a pressurized cylinder. During exposure to bottled air, if the meter still does not read 20.9%
(especially if it is higher), adjust the oxygen Gain to reference clean air.
The electrochemical oxygen cell current output is directly proportional to the partial pressure of the oxygen in the
atmosphere surrounding the cell. The partial pressure of oxygen is a function of the percent by volume of oxygen in the
air and the air pressure.
Air pressure varies as natural weather systems move through the area, causing changes in barometric pressure as well as
oxygen content. The barometric pressure changes cause a relatively small change in oxygen content indication; for
example, if the gain is set to give an oxygen content meter indication of 20.9% oxygen when the barometric pressure is
29.9 inches of mercury, normal variations of barometric pressure cause variations in meter readings of + 0.25%, from
20.75% to 21.15%.
If the gain is set during a normal high pressure weather cycle, the variation is 0.50% downscale; conversely, if the gain is
set during a normal low, the variation is upscale.
This response to atmospheric pressure is not distressing when understood. The variation of the alarm point by + 0.25% is
not significant when the liberal safety factor between the alarm point, usually 19.5%, and the point at which oxygen
deficiency first emphatically affects human performance, approximately 16%, is taken into consideration.
P RECAUTIONS
D O N OT : expose the oxygen cell to temperatures below 32 F (0 C) or above 130 F (55 C).
N EVER : adjust the oxygen cell when the air passing over it may be oxygen deficient. Always adjust the cell in the
presence of CLEAN AIR.
A VOID : gross exposure to toxic gases. Pure gases, liquid hydrocarbons (butane, propane, gasoline etc.), lacquer fumes,
and cigarette smoke should be kept away from the oxygen cell.
If you wish to recalibrate to a different alarm point, consult an authorized ENMET service center or ENMET personnel
directly.
5.4 Humidifier
Periodically check the humidifier water level, and add water when required to maintain proper water level. Operating
the equipment with a dry air sample and no water in the humidifier bowl renders the carbon monoxide sensor
ineffectual.