Det-Tronics C7051B, C UV Flame Detector - Manual (Page 15)

In general, fire detectors should be placed as close as
practical to the probable hazard. The (blinded) nuclear
surveillance module of the C7051 Detector must be posi-
tioned at least as close, if not closer, to the source of
radioactive interference as the fire detector module. See
Figure 1.
Det-Tronics systems may be adjusted to various sensitiv-
ity levels by programming the controller to respond at a
pre-determined detector count rate. This count rate is
dependent upon the intensity of ultraviolet radiation
reaching the detector, which is a function of fuel, flame
size, distance from the detector and the amount of UV
absorbing vapors present. Programming the controller
to respond to a low count rate results in high system sen-
sitivity. Conversely, programming the controller to
require a high count rate results in low system sensitivity.
The possible presence of UV absorbing vapors must be
examined closely. Some chemical and petrochemical
vapors have very strong UV absorption characteristics.
For a listing of UV-absorbing vapors, contact Detector
Electronics Corporation, Customer Service.
NOTE
Do not mount UV detectors close to the ceiling in
enclosed areas if dense smoke may be expected
to accumulate at the onset of a fire. Mounting the
detector on side walls a few feet (or about 1
meter) down from the ceiling will normally allow
time for the detectors to respond before they are
affected by smoke rising to the ceiling. It is also
advisable to shorten the time delay settings for
applications where smoke may accumulate dur-
ing a fire. A smoke/fire detector is available for
use in applications where dense smoke might
accumulate prior to the presence of flame (as in
an electrical fire). Consult Detector Electronics’
Customer Service department for details.
MOUNTING AND WIRING THE DETECTOR
The wiring to each detector must be 22 gauge (0.643
mm diameter) minimum, with at least a 600 volt rms rat-
ing. The B-leads from each detector must be individual-
ly shielded. If the B-leads are run in conduit, the conduit
must not be used for wiring from other electrical equip-
ment. Shielded wiring is recommended for the A-leads
and the D-leads. The A-lead can be common to all
detectors connected to one controller, but each detector
must have a separate D-lead to the controller to operate
the
oi system. Each detector may be located at a dis-
tance of up to 2000 feet (600 meters) from the controller.
A grounding screw is provided inside the housing for
connecting the C7051 to earth ground. It is recom-
mended that a conduit seal, drains and breathers be
used. Seals should be installed immediately behind the
detector module to provide a watertight enclosure. In
some applications, alternate changes in temperature
and barometric pressure cause “breathing,” which
allows the entry and circulation of moist air throughout
the detector and connected conduit. Joints in the con-
duit system and its components are seldom tight enough
to prevent this breathing. Moisture in the air condenses
at the base of vertical conduit runs and equipment enclo-
sures, and will build up over a period of time. This can
be detrimental to electronic devices. To eliminate this
condition, explosion-proof seals, drains and breathers
(such as Crouse-Hinds type ECD) should be installed to
automatically bleed off accumulated water.
The following steps should be used for mounting and
wiring the detectors:
1. Detectors should be located for the best unob-
structed view of the area to be protected.
Detectors must be accessible for cleaning the win-
dow and reflector rings.
The blinded detector module should be mounted
as close as or closer than the fire detector module
to the source of radioactivity. For outdoor applica-
tions, fire detectors should be aimed downward to
prevent the cone of vision from scanning the hori-
zon, because the detectors could respond to long
duration lightning flashes. If the detectors are not
pointed straight down, they should be mounted
with the UV test lamp of the fire detector module at
the module’s highest point, if feasible. Otherwise,
dirt accumulation between the window and the
reflector ring might interfere with the Automatic
oi
function. See Figure 10 for mounting dimensions.
2. Disassemble the detector enclosures by turning
the housing covers counterclockwise. See Figure
2 for an example of the detector assemblies.
3. Connect the terminal cap to the conduit or the
optional swivel mounting bracket so that the wires
from the controller can be installed and trimmed.
4. Connect A-, B-, and D-leads to connections in ter-
minal block.
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