Detcon FP-624C - Manual (Page 4)

3.0.3 Base Connector Board
The base connector board is mounted in the
explosion proof enclosure and includes: the
mating connector for the control circuit,
reverse input and secondary transient suppres-
sion, input f ilter, alarm relays, lugless termi-
nals for all f ield wiring, and a terminal strip
for storing unused programming jumper tabs.
The alarm relays are contact rated 5 amps @
125 VAC, 5 amps @ 30 VDC and coil rated
at 24 VDC. Gold plated program jumpers are
used to select either the normally open or
normally closed relay contacts.
3.0.4 Explosion Proof Enclosure
The sensors are packaged in a cast metal explosion proof enclosure. The enclosure is f itted with a threaded cover
that has a glass lens window. Magnetic program switches located behind the transmitter module face plate are acti-
vated through the lens window via a hand-held magnetic programming tool allowing non-intrusive operator inter-
face with the sensor. All calibration and alarm level adjustments can be accomplished without removing the cover
or declassifying the area. Electrical classif ication is Class I; Groups B, C, D; Div. 1.
3.1 P RINCIPLE OF O PERATION
Method of detection is by a controlled rate of diffusion/adsorption. Air and gas diffuse through a sintered stainless
steel f ilter and contact both the active and reference detector beads. The surface of the active detector promotes
oxidation of the combustible gas molecule while the reference detector has been treated not to support this oxida-
tion. The reference detectors serve as a means to maintain zero stability over a wide operating temperature range.
When combustible gas molecules oxidize on the surface of the active detector, heat is generated, effectively chang-
ing the electrical conductance of the active detector. Electronically, the detectors form part of a balanced bridge cir-
cuit. As the active detector changes in electrical conductance, the bridge circuit unbalances. This change in output is
conditioned by amplifier circuits that are an integral part of the assembly. The sensor response and clearing character-
istics are quite rapid resulting in a method of continuous and accurate monitoring of ambient air conditions.
Model FP-624C Combustible Gas Sensor PG.4
NC
ALARM 1
W
H
T
B
L
K
Y
E
L
B
LU
MA
VDC Power In
NO
NC
NO
NC
NO
N
O
/N
C
C
O
M
N
O
/N
C
C
O
M
N
O
/N
C
C
O
M
FAULT ALM-2 ALM-1
Alarm Dry Contacts
ALARM 2
FAULT
R1
A
B
A
B
4-20 mA Output
RS-485 In
RS-485 Out
Optional Voltage
Developing Resistor
Use 250 ohm 1/4w
JUMPERS
UN-USED
Jumper Programmable Alarm Outputs
Normally Open or Normally Closed
Sensor
Place un-used alarm programming
jumper tabs here
detcon inc.
Program Switch #2
FLT
ALM
1 CAL
MicroSafe™ LEL Gas Sensor
HOUSTON, TEXAS
PGM 2
PGM 1
ALM
2
MODEL FP-624C
CONTRAST
Alarm & Cal LEDs
Program Switch #1
Menu Driven Display
Plug-in Microprocessor Control Circuit
Display Contrast Adjust