Detcon DM-200 - Manual (Page 10)

Model DM-200
DM-200 Instruction Manual Rev. 2.0 Page 6 of 40
advisable to calibrate with interference gases. They should be used only as a guide.
2.3 Field Wiring Table (4-20 mA output)
Detcon UniTox™ toxic gas sensor assemblies require two-conductor connections 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.
Table 1 Wire Gauge vs. Distance
AWG Wire Dia. Meters Feet
Over-Current
Protection
22 0.723mm 700 2080 3A
20 0.812mm 1120 3350 5A
18 1.024mm
1750 5250 7A
16 1.291mm 2800 8400 10A
14 1.628mm 4480 13,440 20A
NOTE: This wiring table is based on stranded tinned copper wire and is designed to serve as a
reference only.
NOTE: Shielded cable may be required in installations where cable trays or conduit runs
include high voltage lines or other sources of induced interference.
2.4 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 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 concentrated
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.