MSA FlameGard 5 UV/IR-E Instruction Manual page 7

Ultraviolet Region
UV Detector's
Spectral
Sensitivity
185nm 260nm
Figure 2 Spectral Response of UV and IR Detectors
UV/IR Flame Detector
The FlameGard 5 UV/IR-E is a discriminating UV/IR Detector, which makes use of an
ultraviolet radiation sensitive phototube in addition to an infrared detector (see figure 2).
This combination provides a flame detection system, which is highly immune to false
alarms.
The UV portion of the detector, as described in UV Detector, is combined with an infrared
detector, which reacts to changes in the intensity of infrared radiation. By sensing very
specific wavelengths in both the UV and IR spectra and then processing these signals with
a microcomputer, a very high degree of discrimination is achieved.
Incorporated in the IR circuitry is a flicker discrimination circuit. This permits the detector to
ignore steady IR sources such as hot objects. The inherent flickering of flame provides the
necessary modulation to activate the IR circuit.
Since a flame is a copious source of both ultraviolet and infrared radiation, discrimination is
provided when both UV and IR emissions are detected. If only UV is detected, as in the
case of arc welding, no alarm is given. If only IR is detected, such as a large modulating
hot object, no alarm is given. However, if both conditions are met in the correct
combination and intensity, as determined by an algorithm in the microcomputer, a fire is
identified and the alarm outputs are activated.
Visible Region
Sun's Radiation
Reaching the Earth
Wavelength
4
FlameGard 5 UV/IR-E
Infrared Region
IR Detector's
Spectral
Sensitivity
4.35um