Detcon FP-424C - Manual (Page 8)

5.2 Remote Mount Considerations
If the application requires that the sensor head be remotely mounted away from the transmitter, maximum
line resistance should be 1/2 ohm. Use the wiring table below.
AWG Maximum Length (feet)
20 50
18 75
16 125
14 175
5.3 Sensor Location
Selection of physical sensor location is critical to the overall safe performance of the product. Five factors
play an important role in selection of sensor locations:
(1) Density of the gas to be detected
(2) Most probable leak sources within the industrial process
(3) Ventilation or prevailing wind conditions
(4) Personnel exposure
(5) Maintenance access
Density - Placement of sensors relative to the density of the target gas is such that sensors for the detection
of heavier than air gases should be located within 2-4 feet of grade as these heavy gases will tend to settle
in low lying areas. For gases lighter than air, sensor placement should be 4-8 feet above grade in open areas
or in pitched areas of enclosed spaces. Give consideration to easy access by maintenance personnel as well
as the consequences of close proximity to contaminants that may foul the sensor prematurely.
Leak Sources - Most probable leak sources within an industrial process include flanges, valves, and tubing
connections of the sealed type where seals may either fail or wear. Other leak sources are best determined
by facility engineers with experience in similar processes.
Ventilation - Normal ventilation or prevailing wind conditions can dictate efficient location of gas sensors
in a manner where the migration of gas clouds is quickly detected.
Personnel Exposure - The undetected migration of gas clouds should not be allowed to approach concen-
trated personnel areas such as control rooms, maintenance or warehouse buildings. A more general and
applicable thought toward selecting sensor location is combining leak source and perimeter protection in
the best possible configuration.
Note: In all installations, the sensor in stainless steel housing points down relative to grade (Fig. 1).
Improper sensor orientation will result in false reading and permanent sensor damage.
Detcon Model FP-424C Combustible Gas Sensor PG.8
EYS
Seal
Fitting
Drain
“T” Plug any unused ports.
Figure #1