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November 2020
3.3
Sensor end of life diagnostic
The sensor performs an automatic test daily to ensure its integrity. It performs this test
one hour after initial power-up and then every 24 hours after that.
Note that sensor end of life indication is not available on the oxygen (Net Safety ST340 or
ST341) sensors.
During the test cycle, a period of 10 seconds, the sensor response time should increase to
less than 60 seconds.
If a sensor end of life indication fault is generated, the analog output of the associated
transmitter will be 2.5 mA (fault condition) for a period of 10 seconds. The analog output
will then return to its operational state (4 mA with no gas present) for a period of 50
seconds. This cycle will continue until the sensor has been replaced. When using the Net
Safety M21 or M22 transmitter, the display will read "Sensor Reached Life End" on the
respective channel, and the gas concentration will not be shown.
If used with a Net Safety Millennium II transmitter with relay capabilities, the sensor end of
life diagnostic will be indicated through the fault relay. The fault relay will change states
(de-energize, indicating a fault condition,) upon the detection of the end of life condition.
The fault relay will stay de-energized as long as the fault condition is present. When the
sensor has detected an end of life condition, the alarm relay will not provide an alarm
condition if gas is present; therefore, Emerson recommends replacing the sensor as soon
as possible. For further information on the operation of the relays, please refer to the
associated transmitter manual
Reference Manual
Note
Net Safety recommends monitoring the fault signal (2.5 mA) and fault relay (if available)
to indicate sensor faults if using a fire and gas system or other control system.
Due to the electrochemical sensor technology used in the Net Safety ST3 sensors, the
sensor end of life diagnostic may indicate a sensor with decaying response or a non-
responding sensor.
Contact Net Safety for replacement sensor modules.
3.4
Sensor communication
The Net Safety ST3 sensor uses a proprietary protocol to communicate with the Net Safety
Millennium II series of transmitters.
Never connect this sensor to any device other than the Net Safety Millennium II series of
transmitters. Selected DIP switches and menu options allow communication between the
transmitter and sensor. The sensor's memory stores confituration settings. Incorrect
settings will cause the sensor to not communicate properly with the transmitter. If any
problems develop, please refer to Troubleshooting.
20
(Net Safety Millennium II Multi-Channel Transmitter
or
Net Safety Millennium II Basic Transmitter Reference
Reference Manual
00809-0100-4303
Manual).
Emerson.com/FlameGasDetection
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