Detcon FP-424C - Manual (Page 3)

1.0 D ESCRIPTION
Detcon Model FP-424C combustible gas detection sensors are designed to monitor ambient air for com-
bustible hydrocarbons in the lower explosive limit range (0-100% LEL). The sensor assembly consists of a
plug in replaceable matched pair of catalytic beads mounted in a stainless steel housing, a 12-28 VDC 4-20
mA DC control transmitter, an explosion proof junction box, and a machine fitted rain shield.
1.1 Catalytic Detector
The catalytic detector is supplied as a matched pair of elements mounted in a plug-in replaceable housing.
One element is an active catalytic detector and the other is a non-active compensating element. Each ele-
ment consists of a fine platinum wire embedded in a bead of alumina. A catalytic mixture is applied to the
detecting element while the compensating element is treated so that catalytic oxidation of gas does not
occur. The beads are mounted in a plug-in module that is enclosed by a sintered porous stainless steel
flame arrestor. The plug-in sensor module uses gold plated pins and mounts inside the stainless steel sen-
sor head via mating gold plated sockets.
1.2 Control Transmitter Circuit
The control transmitter is a remote mounted electronic circuit designed and packaged as a plug-in module.
The transmitter assembly consists of several circuit functions: input power conditioning, sensor heater con-
trol, sensor signal conditioning, sensor fault supervision, and fault LEDs. A metallic face plate with pull
ring identifies test points and calibration adjustments. The plug-in module design supports easy field level
maintenance and repair. The mating plug is gold plated for maximum resistance to corrosion.
1.3 Terminal Connector Board
The terminal connector board is mounted in the explosion proof enclosure and includes: the mating con-
nector for the control circuit, reverse input and secondary transient suppression, input filter and terminals
that do not require lugs for all field wiring.
Detcon Model FP-424C Combustible Gas Sensor PG.3
Alumina Bead
Platinum Wire
Catalyst
Construction of
Detector Bead
Sintered Stainless Steel Can
Header
Gold Plated Pins
Beads
BRDG
FP-424C
+
% LEL
4-20 mA DC
T E
X A
S H O U S
T O
N
VOLT
detcon inc.
ZERO
BRIDGE
SIGNAL
FLT
DET
FLT
FINE
COARSE