Detcon DM-400IS - Manual (Page 14)

3.4 I NSTALLATION
Optimum performance of ambient air/gas sensor devices is directly relative to proper location and installation practice.
3.4.1 Field Wiring Table (4-20 mA output)
Detcon Model DM-400IS toxic gas sensor assemblies require two conductor connection between power supplies and
host electronic controllers. Wiring designators are + (DC), and – (DC). Maximum single conductor resistance between
sensor and controller is 10 ohms. Maximum wire size for termination in the sensor assembly terminal board is 14 gauge.
AWG Meters Feet
20 240 800
18 360 1200
16 600 2000
14 900 3000
Note 1: This wiring table is based on stranded tinned copper wire and is designed to serve as a reference only.
Note 2: Shielded cable may be required in installations where cable trays or conduit runs include high voltage lines or
other sources of induced interference.
Note 3: The supply of power must be from an isolating source with over-current protection as follows:
AWG Over-current Protection AWG Over-current Protection
22 3A 16 10A
20 5A 14 20A
18 7A 12 25A
3.4.2 Sensor Location
Selection of 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.
Leak Sources - Most probable leak sources within an industrial process include f langes, 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 eff icient 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 concentrated person-
nel 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.
Maintenance Access
Consideration should be given to easy access by maintenance personnel as well as the consequences of close proximity
to contaminants that may foul the sensor prematurely.
Note: In all installations, the sensor element in SS housing points down relative to grade (Fig. 1). Improper sensor ori-
entation may result in false reading and permanent sensor damage.
DM-400IS Toxic Gas Sensors PG.14