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SYSTEM DESCRIPTION
The R7404/C7050 UV detection system consists of an
R7404 Controller and up to 16 C7050 Detectors.
DETECTOR
The C7050 Detector responds to UV radiation over the
range of 1850 to 2450 angstroms. It is insensitive to direct
or reflected sunlight and to normal artificial lighting.
The output of the detector consists of a series of voltage
pulses or “counts.” The frequency of these pulses is
directly proportional to the intensity of the radiation being
detected and is measured in counts per second (cps).
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The detector is equipped with the Automatic
oi
feature
(Figure 1). A UV test lamp is mounted in the same
enclosure with the UV sensor tube, but they are optically
isolated from each other by a cylindrical shield. When
the test lamp is actuated by a signal from the controller,
it generates a UV test signal that travels out through the
viewing window, where it encounters the reflective
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ring
and is directed back through the window to the sensor.
The controller evaluates the strength of the return signal
to determine the relative condition of the detector and
its optical surfaces. Since this UV test signal must pass
through the same portion of the viewing window as UV
radiation generated by a flame, a reliable test of the ability
of the detector to “see” a fire is achieved.
The controller continuously executes the automatic
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test, sequentially testing each detector connected to it. If
a fault should occur in the system, it is quickly detected
and registered on the digital display on the front panel of
the controller and the Fault output is de-energized.
Internal Reflection
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The use of an Internal Reflection
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detector is
recommended in applications where corrosive or oily
contaminants are present in the atmosphere. This type
of environment can cause rapid deterioration of the
reflectivity of externally mounted
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rings, resulting in
the need for frequent detector maintenance. Since the
Internal Reflection detector checks the cleanliness of the
viewing window without the use of an external reflective
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ring, faults caused by corrosion or contamination of
the ring are eliminated. A fault will be indicated only if the
viewing window is actually dirty. It is important to note
that the internal reflection system is effective only with oily
substances that wet the surface of the window. It does not
detect dry contaminants and, therefore, is not practical
for powder coating booths or similar applications where
various dry contaminants can obscure the vision of the
detector.
UV detectors that are currently using the external
reflection
oi
system can easily be converted to Internal
Reflection in the field by simply replacing the existing
sensor tube module with a DE1888V Internal Reflection
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Tube Module. No calibration or other adjustments are
required, and no modifications to the detector enclosure
are needed.
Detector Enclosure
The detector is housed in an explosion-proof enclosure
that is designed to meet most national and international
standards. It is available in various materials to meet
the requirements of the environment in which it is used.
Materials include anodized aluminum, nickel-plated brass
and 316 stainless steel. The aluminum and the nickel-
plated brass housings are epoxy coated, making them
suitable for use in high saline atmospheres, such as
offshore platforms.
The detector is typically mounted on an optional
swivel mounting assembly (Model Q9001), which is
recommended for ease in installation. Other mounting
arrangements are also available, such as a quick-
connect front mount for applications involving paint spray
or powder coating booths, or for looking inside mixers,
kettles, conveyors and other inaccessible areas.
CONTROLLER
The R7404 is designed for use with 24 volt dc power
supplies, but will operate from any direct current supply
between 10 and 38 volts. The unit will tolerate transients
such as those that can occur when fully discharged
batteries are placed on charge. When power is present
at the R7404 Controller, it is indicated by a continuously
energized green LED. All other lights and displays on
the R7404 panel are normally off, but may be periodically
UV DETECTOR
UV TEST LAMP
OPTICAL SHIELD
VIEWING WINDOW
SNAP-IN
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RING
UV SENSOR
C784
Figure 1—Detector with oi
