95-84751.1 2
4. The sensor should be located in an area where it
is safe from potential sources of contamination.
5. The sensor should be pointed down to prevent
the buildup of contaminants on the gas inlet.
6. The sensor must be accessible for testing and
calibration.
7. Exposure to excessive heat or vibration can result
in pre-mature failure of electronic devices and
should be avoided if possible. Shield the sensor
from intense sunlight to reduce solar heating.
IMPORTANT
All diffusion-based gas sensors must contact the
target gas in order to provide an accurate gas
measurement. This must always be remembered
when selecting locations for gas sensor
installation.
For additional information on determining quantity and
placement for sensors in a specific application, refer
to Instrument Society of America (ISA) Transaction
Volume 20, Number 2, titled “The Use of Combustible
Detectors in Protecting Facilities from Flammable
Hazards.”
GENERAL WIRING REQUIREMENTS
Wire Size and Type
In applications where the wiring cable is installed in
conduit, the conduit must not be used for wiring to
other electrical equipment.
Three wire shielded cable is highly recommended for
connecting the PointWatch to the controller. A foil
shield is recommended.
The maximum wiring distance between the
PointWatch and controller is limited by the gauge of
the wire being used. Refer to the PointWatch
manual for specific information on maximum loop
resistance.
CONDUIT SEALS, DRAINS, AND BREATHERS
When installing the PointWatch in hazardous areas
where explosion-proof equipment certification is
required, explosion-proof conduit seals should be
installed within 18 inches (46 cm) of the junction box
to prevent the passage of vapors or flames through
the conduit. Seals are recommended even if they are
not required by local wiring codes.
Conduit systems are never completely air-tight. As a
result, significant amounts of condensation can form
within the conduit system. Therefore, it is important to
take proper precautions during installation to ensure
that accumulated moisture will not cause damage to
the components of the system.
Conduit raceways should be inclined so that water
will flow to low points for drainage and will not collect
on conduit seals or inside enclosures. If this is not
possible, install conduit drains above the seals to
prevent the collection of water, or install a drain loop
below the detector with a conduit drain at the lowest
point of the loop.
Conduit drains should be installed at water collection
points to automatically drain accumulated moisture.
Conduit breathers should be installed at upper
locations to provide ventilation and allow water vapor
to escape. At least one breather should be used with
each drain.
When using steel wire armored or mineral-insulated
copper-sheathed cable, select an approved gland
with a watertight compression stage and an overall
gland shroud for outdoor applications. A sealing
washer must be fitted between the gland and the
conduit/cable entry to ensure IP66 rating.
CONTROLLER WIRING
Field Wiring Connector
The controller is furnished with a field wiring
connector backplate that incorporates pressure type
screw terminals for connecting the external wiring and
a circuit board edge connector for attaching to the
controller. The use of a mounting rack is
recommended for mounting the controller. The
backplate is attached to the back of the rack to allow
easy removal of the controller without disturbing the
wiring. See Figures 1 and 2.
The controller is designed for installation in a non-
hazardous area.
Figure 3 shows the terminal configuration for the
R8471H Controller.
Terminals 1 and 2 – 4 to 20 ma dc output.
Non-Isolated Current Output -
If the 4 to 20 ma current loop is
to be non-isolated, wire the
system as shown in Figure 4.
Note that terminal 2 is not used
with a non-isolated current loop.
Program the unit for a non-
isolated current loop as
described in the “Controller
