GAS LEAK DETECTORS
5
Normal operation
Malfunction
Alarm
After the warm-up time, the gas leak detector enters normal operating condition. Under this condition, the leak
detector performs self-diagnostics of the electronic circuit. A green LED light indicates “power on” and normal
operating condition of the unit.
If a malfunction occurs (e.g. breakage of the sensor element) the leak detector indicates the fault by showing a
yellow LED light. A flashing yellow LED indicates reaching the expected working life of the instrument (10 years).
After such indication, the leak detector operates normally but its replacement is recommended (the internal sensor
element is subject to natural aging).
The “Gas Sentinel” gas leak detector is provided with an alarm delay timer to avoid faulty indications due to
momentary increases in concentration of the gas. When the alarm threshold is exceeded, the intermittent optical
(red LED) and audible (internal buzzer) alarms are given. If the gas concentration exceeds the first alarm threshold
10% LEL, just the first red LED lights up, while if the concentration exceeds the second threshold 15% LEL, both
red LEDs light up. If the alarm persists for a time exceeding 30 seconds, the gas leak detector enters the alarm
status: the alarm light becomes steady and the buzzer is activated, while the relay causes closing of the solenoid
valve. The alarm and closing of the solenoid valve are activated at the first or second gas concentration depending
on the gas leak detector. When the concentration of the gas goes below the threshold alarm the gas leak detector
stops the alarm automatically and resets the normal functioning conditions. By pushing the “Prog” button it’s
possible to stop the alarm for 1 minute.
To check for correct performance of the “Gas Sentinel” gas leak detectors, using a gas bottle test, discharge a
small quantity of gas at the opening and wait. If necessary, repeat the operation. The instrument will indicate the
presence of gas with a beep and lighting up of one or two intermittent red LEDs. If the gas is detected for more
than 30 seconds (internal delay provided in order to avoid spontaneous signalling), the alarm configuration (red
LED lit up and buzzer on) is activated. After the set delay time, the pilot relay of the solenoid valve will also be
energized. Test functioning by a common lighter is not recommeded, as it makes the gas concentration peak too
high, resulting in the sensor giving an incorrect reading for a week.
Performance tests
The “Gas Sentinel” gas leak detectors have provision for simultaneous monitoring, through a serial
communication link, of up to 11 zones. This is done by a programming procedure whereby one detector is set as
the main one (Master) and the other 10 detectors as secondary (Slave units).
When the solenoid valve is present, it must be connected to the Master leak detector.
When installing two or more leak detectors in network, the alarm condition produced in a slave detector will also
cause the alarm in the master and closing of the solenoid valve to which it is connected. The flashing green LED
on the master indicates that the alarm has been transmitted by a slave unit.
On the other hand, the alarm produced in a master will not cause activation of the slaves.
Networking
The “Gas Sentinel” gas leak detectors, with sensors of semi-conductor type, are calibrated individually in cells with
the specific gas after an extended stabilizing warm-up of the sensor.
This guarantees maximum security of the gas leak detector for the user because :
- the sensors are calibrated under conditions identical to actual operating conditions;
- the warm-up ensures maximum stability in the level of calibration of the sensor.
The semi-conductor type of sensors used in the gas leak detectors combine the advantage of increased
sensitivity over a period of time with good selectivity characteristics and long working life.
RELIABILITY OF THE SENTINEL GAS LEAK DETECTORS
