General Monitors TA402A, Instruction Manual

Page: 32 / 51

6.2 UV Phototube
The UV phototube is used in the Models
FL3000, FL3100, FL3001, FL3101. This
phototube responds to UV radiation within a
range of 185nm to 260nm (wavelength).
The shortest wavelength of energy from the
Sun (figure 30), that reaches the Earth’s
surface is about 300nm. Therefore, the UV
phototube will not respond to energy from
sunlight.
6.3 Pyroelectric Device
The pyroelectric device is used in the
Models FL3000 and FL3002. This device
responds to a change in IR radiation with a
wavelength centered on 4.3 microns (figure
29). The circuit using the pyroelectric
device in the detector is designed such that
the ‘flicker rate" of IR radiation from a
flame can be compared with the known
“flicker rate” of fire.
6.4 Thermopile
The thermopile device is used in the Model
FL3002. This device measures the intensity
of IR radiation with a wavelength centered
on 4.3 microns. The thermopile device will
not respond to energy from sunlight at this
wavelength because most of it is absorbed
(or attenuated) by carbon dioxide in the
atmosphere.
27
Detector Assembly/Accessories
General Monitors
Fig ure 32