Coster RFG 749 Manual

GAS LEAK DETECTOR WITH INTERNAL SENSOR
AND RELAY OUTPUT
RFG 749
• Power supply 220/240 Volts ac
• Internal sensor with alarm level set at 0.3% of gas in air
• Voltage-free SPDT output relay
• Suitable for control of valves N.O. or N.C. or of aeration fans

APPLICATION

RFG 749 gas leak detector is designed to ensure the safe use in
domestic and other non-industrial premises of domestic appli-
ances running on gas, such as: cookers, boilers and calorifiers.
It is able to monitor the concentration in the air of the usual types
of combustible gases such as: town gas, natural gas, LPG and
propane. The output relay can control a safety shut-off valve, an
aeration fan or a remote alarm.

OPERATION

The LED on the facia, when lit, indicates that RFG 749 is receiv-
ing power (fig. 2.3). When the power comes on, the detector
does not activate the alarms for 1.5 - 2 minutes which is the
period necessary for the sensor to become stabilized. After this
period the detector is ready to sound the alarm.
The internal sensor monitors the concentration level of gas in the
surrounding air and the detector, in the event that this concentra-
tion exceeds the level of alarm, sets off an audible warning and
activates the output relay which can control a gas safety shut-off
valve or a fan for changing air.
The alarm level is equivalent to a concentration of 0.3 % of gas in
the air, that is, about 1/20 of the concentration necessary to
render the gas-air mixture explosive. This allows action to be
taken under conditions of maximum safety in the event of an
alarm.
The alarm state, once acquired, will continue even if the concen-
tration of gas should return below the level of alarm. In order to
reset the detector to its normal state it is necessary to press the
button located on the facia below the LED (fig. 2.4).

CONSTRUCTION

RFG 749 is constructed in two parts:
• Base (fig. 2.2) suitable for wall mounting, in self-extinguishing
plastic, comprising:
– Terminal block for electrical connections (fig.3.1) protected
against accidental contacts.
– Cable entry for passage of leads from rear (fig.3.3)
– Cable entries for passage of leads from below (fig.3.4)
– Screw holes for attaching to wall (fig. 3.5)
• Detector (fig. 2.1), enclosed in a casing made from self-extin-
guishing plastic, which includes the electronic circuit (con-
structed according to standards of Italian Electrotechnical Com-
mittee - CEI), the sensor, the output relay and the alarm buzzer.
On the facia are located the power supply indicator LED (fig.
2.3) and the reset button (fig. 2.4).
The output relay is airtight and is filled with inert gas which, by
preventing the formation of sparks, ensures the maximum safety
of operation.
The casing is secured to the base by four retaining clips and the
electrical connections between the electronic circuit and the
terminal block are by means of pins which are pressed directly
into the terminal sockets.

INSTALLATION

The correct location of RFG 749 is essential for its correct opera-
tion and depends on the type of gas to be monitored and its
density in respect of air.
DISCONTINUED PRODUCT
TO SEE A SUITABLE REPLACEMENT PRODUCT

TYPICAL INSTALLATION

Type of gas
Natural gas (light)
LPG (heavy)
G 120
Eng. 03.91
fig. 1
NATURAL GAS
LPG
Position
20 to 60 cm. from the ceiling
20 to 60 cm. from the floor
1