Det-Tronics C7051B, C UV Flame Detector - Manual (Page 14)

OPTIONS AVAILABLE
• R6006 Relay Output Module to be used in conjunc-
tion with the R7404 when relay switching contacts are
required. Four models are available. The R6006A
has six fire relays, one fault relay, and one alarm relay.
The R6006B has eight fire relays. The R6006C and D
are functionally identical to the R6006A and B
respectively, with the addition of an output load mon-
itoring feature. The relays in the R6006 have form C
(normally open/normally closed) contacts that are
capable of operating fire alarm devices requiring up
to 3 amperes at 30 vdc or 250 vac. Refer to form 90-
1016 for more information.
• W4220 Voltage Converter for operating the R7404
from line (mains) voltage. The W4220 Voltage
Converter is designed to furnish operating power for
up to eight modules of the Det-Tronics Fire Detection
System. It is available with either two or four chan-
nels, each separately fused and completely sepa-
rate. Should a fault occur in one channel, the others
are unaffected. It is styled and sized to be compati-
ble with other modules when mounted with them in
the Det-Tronics Q4004 Mounting Cage. Refer to form
95-8243 for more information.
• Q4004 Mounting Cage (Figure 9) designed for hold-
ing up to 8 modules in a standard 19 inch instrument
rack. The Q4004 is recommended for ease of instal-
lation and service.
DETECTOR SENSITIVITY
The Detector Electronics ultraviolet fire detector uses a
Geiger-Muller type detector designed to respond to radi-
ation over a wavelength of 1850 to 2450 Angstrom units
(10,000 Angstroms = 1000 nanometers = 1 micron =
0.001 millimeter). Figure 6 illustrates the sensor tube’s
range of sensitivity, and compares this range to other
forms of radiation. Note the UV radiation reaching the
earth from the sun does not extend into the detector’s
range of sensitivity. In addition, radiation from normal
(properly screened) artificial lighting (fluorescent, mer-
cury-vapor and incandescent lamps) does not extend
into the detector’s spectral range. As a result, the detec-
tor is insensitive to these forms of radiation and may be
used outdoors or indoors. Some mercury-vapor lamps
can operate for extended periods with cracked or other-
wise damaged envelopes, and will then emit UV radia-
tion in the frequency response range of the Det-Tronics
detector. Defective mercury-vapor lamps can cause eye
irritation and should be immediately removed from ser-
vice.
The UV sensor responds to any radiation which can pen-
etrate its glass envelope and create ion pairs. The glass
envelope absorbs most alpha or beta particles, but it
permits both gamma and x-rays to pass through. If
these rays create ion pairs between the electrodes near
the cathode, the normal discharge process will occur
and the detector will produce a count. If the x or gamma
ray flux is sufficient to produce a count rate higher than
the system sensitivity setting, an undesired actuation of
the system may occur.
By automatically compensating for the extra counts pro-
duced by radioactivity, the C7051 Detector assembly
keeps the UV detection system functional in locations
where radioactivity is present.
SYSTEM SENSITIVITY CONSIDERA-
TIONS
Because of the complexity of the combustion process,
the UV detector count rate generated by different size
fires viewed from the same distance is difficult to predict
with a high degree of precision. In general, however, if a
fire doubles in size, the detector count rate is increased
by approximately 60 percent.
Selection of the controller sensitivity and time delay to be
used in a given application is dependent on the level of
hazard present and the action to be taken in the event of
fire. The adjustable sensitivity and time delay of the
R7404 system allows it to meet the requirements of virtu-
ally any application. For sensitivity and time delay
adjustment information, see the “Installation” section.
INSTALLATION
DETECTOR POSITIONING AND DENSITY
As previously stated, the Det-Tronics detector has a
nominal 90 degree cone of vision. What this means in
practical terms can be understood by reference to a typ-
ical installation. Consider an application with a ceiling
height of 25 feet (7.5 meters) and assume it is desired to
have complete detector coverage at floor level. If a
detector is mounted 2 feet from the ceiling and pointed
straight down, the distance from the detector to the des-
ignated level is 23 feet (7 meters). Because of its 90
degree cone of vision, the detector covers a circular area
with a diameter of 39 feet (12 meters). A simple layout of
the area to be covered will easily reveal the number of
detectors required to completely supervise the designat-
ed area.
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