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SMC sierra monitor corporation Sentry Instruction Manual - Version 6
SERVICE
Page: 72
7.6 OXYGEN MODULE (5100-03)
7.6.1 DESCRIPTION
The Oxygen Module includes the electronic
assembly installed in an explosion proof housing
and the electrochemical sensor connected to one
hub of the enclosure. Cabling from the controller
connects to a three pin spring loaded terminal
strip.
7.6.2 TROUBLE ANALYSIS
Electrical adjustment, or replacement of the sensor
will be necessary under the following conditions:
• Controller displays the following error
messages:
CHANGE SENSOR
SENSOR FAILURE
REPLACE SENSOR
• False readings or alarms are received due to
sensor inaccuracy.
Warning: During sensor adjustments the
concentration reading on the controller will be
inaccurate and alarm level concentrations may be
displayed. If false activation of the alarm relays
will cause a problem disconnect the relay wiring
prior to adjustment or turn the module off using
the "Change Module" mode.
NOTE
Although all the necessary data can be collected with a
voltmeter at the sensor module, some helpful
information can be displayed on the controller or
printed. See diagnostic codes 0004 and 0008 in
Appendix C.
7.6.3 ADJUSTMENT PROCEDURE
Prior to reading voltages and making adjustments perform
a visual inspection to confirm that there are no physical
problems such as water in the electronics enclosure,
wiring damage or corrosion.
Use Figure 7-7 to locate test points during the following
procedures.
7.6.3.1 SIGNAL ADJUSTMENT
It is unlikely that any electrical adjustment will be
required except when a new sensor is installed.
To make the electrical adjustment connect a voltmeter to
SIGNAL OUT (pos) and GND (ground) and use
SENSITIVITY ADJ potentiometer to set the voltage equal to
1/10 of the actual oxygen concentration. In clean air the
concentration is 20.9% so the voltage should be set at
2.09 VDC.
7.6.4 SENSOR REPLACEMENT
The oxygen sensor should be replaced when it can no
longer be calibrated correctly or when the signal output
drops to zero. Generally this is every twelve to eighteen
months. The Sentry clock keeps track of the age of the
sensor if it is correctly initialized in the "change module"
mode.
When a new sensor is installed use the CHANGE MODULE
menu selection to answer yes to the "new sensor?"
question. After nine months the CHANGE SENSOR
message will be displayed to warn that a new sensor
should be installed.
The SENSOR FAILURE message for Oxygen sensors does
not indicate a specific failure of the sensor but indicates
that the sensor is not correctly connected to the
electronics. If this message appears check that the sensor
harness is correctly installed to the connector on the
bottom electronics board.
When sensor replacement is required, open the cover of
the sensor module, remove the transmitter and disconnect
the sensor wiring harness from the back of the transmitter.
Figure 7-7
Cover Plate - Oxygen Module