ENMET PGD2 - Manual (Page 27)

ENMET Corporation PGD2
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12.2 Toxic Sensors
The PGD2 instrument can be fitted with either one or two toxic gas sensors as detailed in the following sections. However, it should be
noted that where an instrument is fitted with two sets of pellistors to provide monitoring of flammable gases up to 100% volume then
only one toxic sensor (3-series type) can be accommodated.
The toxic gas sensors are of the three-electrode electrochemical type and are designated as either the ‘3-series’ or ‘4-series’
(miniature) toxic sensors. The type/s fitted within a particular instrument will depend upon the gas sensing application and also the
physical arrangement of the instrument internally in order to achieve the requirements of the particular intended application.
12.2.1 Cross Sensitivity
The user should be aware that although the toxic sensors are designed to respond to the presence of specific gases they may also
exhibit response to other gases. This is known as their cross-sensitivity.
Some toxic sensors can be supplied fitted with chemical inboard filters to reduce the cross-sensitivities to other gases.
It is not within the scope of this instruction manual to detail the cross-sensitivity of each toxic sensor to each interfering gas. For further
information on this subject contact ENMET customer service.
12.2.2 Temperature Dependence
Toxic sensors exhibit changes in output signal with changes in temperature.
When exposed to sharp changes in temperature the toxic sensor/s will exhibit a transient response which should die away within
approximately 20 seconds.
12.2.3 Stabilization
New toxic sensors when supplied as spares are fitted with a shorting link across the Sensing and Reference terminals which maintain
the sensor in a ‘ready to work’ condition. This shorting link must be removed before the sensor is fitted into the PGD2.
Once a sensor is fitted into the instrument it relies upon the main battery power to maintain its ‘ready to work’ status. If the battery pack
is removed or the battery life is exhausted, the instrument may alarm or display erroneous readings following battery pack
replacement. This is normal when the sensors have not been powered for a prolonged period. Normal readings will continue when the
sensors have been allowed to stabilise (within 2-3 hours following battery pack replacement dependant upon sensor type). This
condition only occurs after a prolonged period without batteries fitted and should not occur during normal battery changing when the
sensors should stabilise within 5 minutes.
Common characteristics
The following characteristics are common to all of the toxic sensor types:-
Common Characteristics of the Toxic Gas Sensors
Expected operating life
- 2 years
Storage life
- 6 months in container provided
Recommended storage temp.
- 0 - 20 degrees C
Operational temp. range
- -20 to +50 degrees C
Relative humidity
- 15 to 90% non-condensing
Pressure range
- Atmospheric ± 10%
Poison sensitivity
- None