Detcon FP-424C - Manual (Page 4)

1.4 Explosion Proof Enclosure
The transmitter electronics are packaged in a cast aluminum explosion proof enclosure and given a baked
epoxy paint finish. The explosion proof enclosure has 3/4” NPT female entry ports. The enclosure is fitted
with a threaded cover. Electrical classification is Class I, Div. 1; Groups B, C, D.
1.5 Rain Shield
The machine fitted rain shield is designed to help prevent obstruction of the sintered stainless steel flame
arrestor as a result of liquid or solid contact. Material of construction is Dupont Delrin.
2.0 P RINCIPLE OF O PERATION
In operation, FP-424C series sensor assemblies are installed in industrial areas where early detection of gas
leaks is most likely. The sensor is powered by 12-28 VDC. Air and gas diffuses through the porous sintered
flame arrestor and contacts the active and compensating detector elements. Electronically, the detector ele-
ments form part of a bridge circuit as shown below. The balance potentiometer is used to set the output of
the bridge circuit referenced to zero gas. As the active detector element reacts to the presence of com-
bustible gas and the compensating element does not react, the bridge voltage output changes. This voltage
change is conditioned by the transmitter circuit to provide for a linear 4-20 mA DC signal output. As com-
bustible gas dissipates and the sensor is returned to a zero gas environment the bridge circuit returns to a
balanced condition. In application, sensor operation is a continuous reading detection/monitoring method.
Detcon Model FP-424C Combustible Gas Sensor PG.4
BLUE
YELLOW MA
24VDC
To Controller
Terminals
BLACK
WHITE
Sensor
–
+
4-20MA