Det-Tronics U7698A, B, C, E Unitized Frequency IR Detector/Controller - Manual (Page 7)

RESPONSE CHARACTERISTICS
Response is dependent on the fuel, the temperature of
the fuel, and the time required for the fire to build. As
with all fire tests, results must be interpreted according
to the individual application.
Typical response distances of the U7698 to various
flammable materials are listed in Table 1. Fuel for the fire
is approximately one pint of liquid or one pound of wood
shavings and is burned in a 1 foot by 1 foot steel pan.
Methane gas fire is performed with the flame approxi-
mately 30 inches high and 6 to 8 inches in diameter. The
U7698 was sited to observe the fire at center axis ± 10
degrees.
Typically, the U7698 will respond in 3 seconds to a high
intensity flickering IR source and within 8 to 10 seconds
to a 1 square foot gasoline fire at 65 feet (approximately
0.1 square meter at 20 meters).
GENERAL APPLICATION
INFORMATION
The U7698B provides reliable response to the infrared
radiation emitted from hydrocarbon fires while remaining
insensitive to solar radiation and artificial lighting.
However, to achieve maximum performance of the fire
protection system, it is necessary to recognize any con-
ditions that can prevent the unit from responding to fire
as well as any sources besides fire that can cause the
detector to respond.
Any object with a temperature greater than 0° Kelvin
(–273°C) emits infrared radiation. The hotter the object,
the greater the intensity emitted between 4.2 and 4.7
microns. The U7698B ignores steady state infrared
sources that do not have a flicker frequency characteris-
tic of a fire. However, it should be noted that if these
steady state infrared sources are hot enough to emit
adequate amounts of infrared radiation in the 4.2 to 4.7
micron range and if this radiation becomes interrupted
from the view of the detector in a pattern characteristic
of a flickering flame, the unit can respond and go into
alarm. The closer the infrared source is to the detector,
the greater the potential for a false alarm.
Arc welding should not be performed within 10 feet of
the detector. Although only a low level of radiation in the
4.2 to 4.7 micron range is emitted by the welding, the
heated metal can become a false alarm source.
The U7698B is resistant to interference by EMI and RFI.
It will not respond to a 5 watt walkie-talkie at a distance
of greater than 1 foot.
The U7698B is a single frequency infrared device with
detection limited to the hot CO2 emission peak, there-
fore, it cannot be used to detect fires that do not contain
carbon, such as hydrogen, sulfur, and burning metals.
INSTALLATION
DETECTOR POSITIONING
The U7698B has an 80 degree cone of vision that covers
a somewhat elliptical area when it is angled to cover the
hazardous area. It is important to note that as the dis-
tance increases between the detector and the fire
source, so does the response time of the detector to a
fire of a given size. For fastest response time, locate the
detector as close as possible to the anticipated fire
source. Be sure that enough detectors are used to ade-
quately cover the hazardous area. For outdoor applica-
tions, the detector should be aimed downward to pre-
vent it from scanning the horizon. This minimizes the
response to distant infrared sources outside the protect-
ed area.
5 95-8353
Table 1—Typical Response Distances
Flammables
Distance From
Detector
Acetone 60 feet (18 meters)
Diesel 60 feet (18 meters)
Gasoline 65 feet (20 meters)
Methanol 50 feet (15 meters)
Toluene 50 feet (15 meters)
Fine wood shavings 50 feet (15 meters)
(excelsior)
Methane 35 feet (10 meters)