ENMET PGD2Manual.pdf - Manual (Page 24)

ENMET Corporation PGD3-IR
21
10.3 Oxygen Sensors
WARNING: The instrument is not designed for use in oxygen enriched atmospheres i.e. greater than 21% oxygen.
The PGD3-IR instrument may be fitted with the oxygen sensor detailed in the following section 10.3.5 to allow measurement of oxygen
deficiency.
The oxygen sensor is contained within a blue coloured plastic moulding normally located behind the instruments’ right hand side gas
inlet as viewed from the front.
10.3.1 Cross Sensitivity
In general, toxic gases at the levels of concentration experienced in normal use have no cross sensitivity effect on the oxygen sensor.
However, acid gases such as CO
2
and SO
2
give a small enhancement (e.g. about 0.3% of signal per 1% CO
2
) to the oxygen reading.
For further information on this subject contact ENMET customer service.
10.3.2 Temperature
The oxygen sensors themselves have a characteristic that varies with temperature. However, this is compensated in the PGD3-IR
instrument software and is therefore insignificant to the user.
10.3.3 Pressure Transients
Oxygen sensors are sensitive to sudden changes in pressure as may be experienced when travelling in a lift shaft or through doors
underground where there is a significant ventilation pressure differential between the two sides of the door(s). Under such
circumstances the instrument may react to the pressure transient, possibly resulting in a temporary alarm condition being given. This
transient will normally fade away after approximately 10 seconds, whereupon the alarm can be reset.
10.3.4 Humidity
Because the humidity in the air affects the volume % concentration of oxygen this will be reflected in the oxygen sensor reading. This
also significantly varies according to temperature as shown by the following tables of approximate figures: -
At 0 degrees C
Relative Humidity % Volume of Oxygen in Air
0% 20.94
50% 20.9
100% 20.84
At 20 degrees C
Relative Humidity % Volume of Oxygen in Air
0% 20.94
50% 20.7
100% 20.45
At 40 degrees C
Relative Humidity % Volume of Oxygen in Air
0% 20.94
50% 20.15
100% 19.42
Therefore if an instrument is calibrated in a laboratory at 20
O
C with ‘dry’ compressed air, the reading will fall when the instrument is
placed into use in an atmosphere having humidity. This can be ‘compensated’ by use of the Sensor Zero function (where enabled) as
described in section 6.15 to give a 20.9% reading if required.
10.3.5 Oxygen Sensor Type and Characteristics
Type No’s 4OX-2
Nominal Range 0-25% Oxygen
Expected Operating Life Two Years in Air
Response Time <15 secs
Temperature Range -20 to +50 degrees C
Pressure Range Atmospheric ± 10%
Operating Humidity 0 to 99% non condensing
Storage Life 6 months in container provided
Storage Temperature 0-20 degrees C
(The above figures are based on conditions at 20 degrees C, 50% RH and 1013 mBar).