Det-Tronics MOS H2S Gas Sensor - Manual (Page 20)

95-8532 1.4 18
CALIBRATION
fREQUENCY Of CaLIbRaTION
The MOS H
2
S sensor is typically utilized to protect human
life. For this reason, a frequent calibration inspection
is recommended. The specific frequency required in
different applications can vary depending upon the
amount of background gas, concentration of exposed
H
2
S, and ambient environmental conditions.
Calibration must be performed:
When a new system is initially put into service. –
When the sensor is replaced. –
Periodically to verify proper performance. –
To ensure optimum performance, the recommended
frequency of calibration for MOS H
2
S sensors is:
After a one hour warm-up period. •
After 24 hours. •
After one week. •
Every 90 days. •
IMPORTANT
To ensure adequate protection, the H
2
S detection
system must be calibrated on a regularly
scheduled basis.
CaLIbRaTION GaS
The U9500B/MOS H
2
S sensor must be calibrated using
only Det-Tronics 40 ppm H
2
S ampoules. All ampoule
calibrations must be performed using Det-Tronics
calibration bottle with thumb screw ampoule breaker and
internal mixing fan. Do not use bottled 40 ppm H
2
S in
nitrogen.
aUTO CaLIbRaTION pROCEDURE
The Infiniti with MOS H
2
S sensor is calibrated using the
Automatic Calibration sequence. All adjustments are
made automatically by the transmitter once calibration
has been initiated. Refer to Table 7 for the Automatic
Calibration Procedure.
IMpORTaNT CaLIbRaTION NOTES
Ensure that only clean air is present at the sensor prior •
to entering the calibration mode. If the possibility
of background gases exists, purge the sensor with
clean air to ensure accurate calibration.
If the calibration procedure is not completed or
•
if the sensitivity of the sensor has deteriorated to
the extent that calibration cannot be successfully
completed, a fault will be generated and the system
will automatically revert back to the former calibration
settings (after 10 minutes or when the gas level drops
below the lowest setpoint). If a successful calibration
cannot be accomplished, replace the sensor and re-
calibrate.
Inspect the sensor. Loss of sensitivity can be
•
caused by various factors. One common cause is
by clogging of the hydrophobic or sintered filter by
dirt, oil, paint, etc. Problems of this nature will not
be detected by the transmitter’s diagnostic circuitry.
If the filter or the sensor are dirty or plugged, they
should be replaced.