Industrial Scientific Oldham MX52, Commissioning, Operating And Maintenance Manual

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3.3. Operating modes
3.3.1. Audio warning device (buzzer)
In normal operation, the audio warning device is triggered whenever a fault or an alarm appears.
The audio warning device can be stopped by pressing the ACKNOWLEDGEMENT key or by
remote acknowledgement. The buzzer makes a continuous or discontinuous sound (according to the
programming of the unit) if an alarm threshold is exceeded.
3.3.2. Light-emitting diodes (LED) (Fig. 26)
Each channel is equipped with five LEDs (visible and identified on the FRONT panel).
LED Extinguished Illuminated
in steady mo de
Flashing
GREEN Channel not in
service
Channel in service Threshold AL1 exceeded
(manual clearing) and not
acknowledged
1st red AL1 not triggered Threshold AL1 exceeded
(automatic clearing)
Threshold AL2 exceeded
(manual clearing) and not
acknowledged
2nd red AL2 not triggered Threshold AL2 exceeded
(automatic clearing)
3rd red AL3 not triggered Threshold AL3 exceeded by mean
or time (automatic clearing)
Yellow No fault Fault on channel -Channel being calibrated or
programmed
- Detector being calibrated
3.3.3. Alarm thresholds
Each of the three alarm thresholds can be programmed independently for each channel. (See the
“Channel programming” menu).
In normal operation, a gas alarm is only triggered after a preprogrammed time delay in order to
avoid spur ious alarms.
Alarm thresholds can be processed in the following manners:
- in normal cycle with manual clearing: block diagram 1,
- in normal cycle with automatic clearing: block diagram 2,
- in parking cycle: block diagram 3.
The alarm thresholds are to be selected according to the gases detected and the corresponding
standards in force.
Special case: A channel connected to a fire detector
- It is MANDATORY to select the scale with 100 divisions.
- It is MANDATORY to select the alarm threshold with 60 divisions.
(Owing to the end-of-loop resistor of 2.7 k
Ω
, the fire detector outputs 4 mA when no fire is detected
and 20 mA if a fire is detected).