Detcon FP-624C - Manual (Page 3)

3.0 D ESCRIPTION
Detcon MicroSafe™ Model FP-624C, combustible gas sensors are non-intrusive
“Smart” sensors designed to detect and monitor combustible gas in air over the
range of 0-100% lower explosive limit (LEL). One of the primary features of the sen-
sor is its method of automatic calibration which guides the user through each step
via instructions displayed on the backlit LCD. The sensor features f ield adjustable,
fully programmable alarms and provides relays for two alarms plus fault as standard.
The sensor comes with two different outputs: analog 4-20 mA, and serial RS-485.
These outputs allow for greater f lexibility in system integration and installation. The
microprocessor supervised electronics are packaged as a plug-in module that mates
to a standard connector board. Both are housed in an explosion proof condulet that
includes a glass lens window which allows for the display of sensor readings as well
as access to the sensor’s menu driven features via a hand-held programming magnet.
The sensor technology is of the catalytic pellistor type. Catalytic pellistors show
a good response to a long list of combustible gases. The technique is referred to as
non-selective and may be used for the detection and monitoring of target com-
bustible gases. Model FP-624C sensors are specif ically designed to be resistive to poi-
sons such as sulf ides, chlorides and silicone. The sensors are characteristically stable
and capable of providing reliable performance for periods exceeding 5 years in most
industrial environments.
3.0.1 Catalytic Detector
The catalytic detector is supplied as a matched pair of elements mounted in a plug-in replaceable housing. One ele-
ment is an active catalytic detector and the other is a non-active compensating element. Each element 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 f lame arrestor. The plug-in sensor module uses gold plat-
ed pins and mounts inside the stainless steel sensor head via mating gold plated sockets.
3.0.2 Microprocessor Control Circuit
The control circuit is microprocessor based and is packaged as a plug-in f ield replaceable module, facilitating easy
replacement and minimum down time. Circuit functions include a basic sensor pre-amplif ier, sensor temperature
control, on-board power supplies, microprocessor, back lit alpha numeric display, alarm status LED indicators, mag-
netic programming switches, an RS-485 communication port, and a linear 4-20 mA DC output.
Model FP-624C Combustible Gas Sensor PG.3
Alumina Bead
Platinum Wire
Catalyst
Construction of
Detector Bead
Sintered Stainless Steel Can
Header
Gold Plated Pins
Beads