Det-Tronics R7495D UV/IR Flame Detection System - Manual (Page 4)

FEATURES
• Controller continuously monitors up to two UV/IR
detectors.
• Ignores false alarm sources such as arc welding, x-
rays, gamma radiation and radiation from f l i c k e r i n g
hot objects.
• Fast response - typically 1 to 5 seconds for an intense
hydrocarbon fire.
• Each detector can independently register an alarm.
• Front panel LEDs indicate fire response and system
fault conditions.
• Microprocessor control.
• All automatic test functions performed with the system
on line.
• Automatic Optical Integrity (oi) for both UV and IR
sensors.
• Field adjustable sensitivity and time delay.
• Explosion-proof (flame-proof) detector housing.
• FM approved, CSA and BASEEFA/CENELEC certified.
• Relay outputs can be set for latching or non-latching
response.
SYSTEM DESCRIPTION
DETECTOR
The C7052J UV/IR Flame Detector is an explosion-proof
device that consists of a UV sensor and an IR sensor
mounted side-by-side on a junction box. This mounting
arrangement allows both sensors to monitor the same
hazardous location with an 80 degree cone of vision.
Either one or two C7052J Detectors can be connected
to one R7495D Controller.
The UV sensor responds to high energy radiation with
wavelengths from 0.185 to 0.245 microns (1850 to 2450
angstroms). See Figure 1. It detects radiation from
sources such as fire, arc welding, lightning, x-rays and
gamma rays. However, it is not sensitive to radiation
from the sun or radiation from flickering hot objects
(blackbodies).
The IR sensor is sensitive to IR radiation over the range
of 4.2 to 4.7 microns. See Figure 1. It is not sensitive to
radiation from the sun, lightning, x-rays, gamma rays, or
arc welding. However, it will respond to fire and flicker-
ing blackbody (heat) radiation sources. IR radiation is
generated by a hydrocarbon flame, which reaches the
detector in pulsations or “flicker.” These pulsations are
present in all flames and are created by turbulent mix-
ing of fuel with air. For this reason, electronic circuitry in
the detector monitors the output of the IR sensing ele-
ment for the appropriate amplitude and a flicker fre-
quency between 1 and 16 cycles per second. If both
the radiation and flicker requirements are met, a fire sig-
nal is generated. This dual criteria for the IR detector
results in increased reliability. However, since the IR
detector responds only to hydrocarbon fires, the UV/IR
detector cannot respond to non-hydrocarbon fires such
as burning hydrogen, ammonia or metal.
The detector junction box contains a +290 vdc power
supply for the UV sensor as well as circuitry to process
signals from both sensors. When both sensors detect a
fire, the IR sensor activates the circuitry in the junction
box to allow the signal from the UV sensor to be sent to
the controller. By using both a UV and an IR sensor, the
C7052J is able to discriminate virtually all false alarm
sources from a true hydrocarbon fire.
oi Feature
Both sensors are equipped with the automatic Optical
Integrity (oi) test feature. This patented system assures
proper operation of the detector by checking the clean-
liness of the optical surfaces, sensitivity of the sensors,
and proper functioning of the electronic components of
the detector once every minute. If a problem should
occur, it is quickly detected. The oi test is accom-
plished without the use of an external UV or IR source.
To minimize the possibility of nuisance fault signals, the
detector must fail the automatic oi test three consecu-
tive times for an oi fault signal to be generated.
The oi test is initiated by a signal from the controller,
which causes actuation of the oi test lamps. A calibrat-
ed low level test beam is generated by the oi test
lamps, as shown in Figure 2. Although the test lamps
are mounted in the same enclosure with the sensor, an
4
Figure 1—Detector Sensitivity Range
5.0 4.0 3.0 2.0 1.5 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
ATMOSPHERIC
TRANSMISSION
WAVELENGTH (MICRONS)
SOLAR
RADIATION
REACHING
THE EARTH
INFRARED
SENSOR
RESPONSE
VISIBLE INFRARED
ULTRAVIOLET
SENSOR
RESPONSE
ULTRAVIOLET
100
75
50
25
0
A1070