GasSens Gas Detection System Section 2 - A14 Receiver Module
O & M Manual
A14-RK, 8/06 2 - 9
Trouble Alarm and Relay
Receivers contain a TROUBLE indicator and an associated SPDT relay. The trouble alarm
will be activated if the transmitter cable is broken or shorted, or if electronic component failure in
either the transmitter or receiver causes a loss of digital input. If these conditions occur, the
TROUBLE indicator will light, the horn will sound intermittently, and the trouble relay will change
state. Note that the trouble relay is a fail-safe relay. Under normal conditions, the coil of this relay
is energized, and it de-energizes when a trouble alarm occurs. The trouble relay will also change
state if power fails.
For systems supplied with the Auto-Test option, the TROUBLE lamp will also indicate the
failure of a sensor to respond to the gas test that occurs automatically every 24 hours. Should
this type of failure occur, the TROUBLE indicator will flash, the trouble relay will change state, and
the audible horn will activate. Pressing the A/R switch will silence the horn, but the lamp and relay
cannot be reset for at least 10 minutes. The flashing TROUBLE light indicates that the sensor
and gas generator should be tested for proper operation using the manual Auto-Test. If the
sensor does not respond, the system should be tested using calibration or test gas as described
in the sensor/transmitter instructions. Pressing the A/R button resets the trouble relay and
indicator.
Auto-Test Function (Optional)
ATI's optional Auto-Test feature is a valuable tool for verifying the proper operation of a gas
detection system while saving manpower normally required for routine testing. Auto-Test is an
electrochemical gas generator fixed to the gas sensor and controlled from the receiver. Every 24
hours, the receiver automatically activates the gas generator and monitors the output of the gas
sensor. When the sensor responds normally, the generator is shut off and the system returns to
normal operation. With this feature in place, operation of every gas sensor is verified daily.
Manual testing is reduced to periodic calibration every 3-12 months, or when the receiver
indicates that a sensor has not passed its normal test.
While an Auto-Test is in progress, the alarm relays are inhibited. This is indicated by the
alternating flash pattern on the WARNING and ALARM indicators used during the 5 minute power
on delay. Typically, an Auto-Test will progress only a few minutes before the sensor begins to
respond. The actual time varies depending on the gas. A chlorine test normally takes less than
30 seconds while a sulfur dioxide test can take as long as four minutes. Alarm relays will remain
inhibited for 10 minutes after completion of the test to allow the sensor to recover. The alternating
flash pattern will continue during this time.
During the first two minutes of the 10 minute inhibit period, alarms are completely inhibited.
The warning and alarm relays will not activate during this period. During the second 8 minute
period, the alarms are only partially inhibited. The inhibit flash pattern will continue during the 8
minute period, but the inhibit will be superseded by an alarm should the measured gas
concentration exceed 50% of range. This means that alarm protection is partially restored to
protect against any major leak during this period. At the end of the 10 minute inhibit period, the
alternating flash will end and the unit will return to normal operation.
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