Emerson Rosemount 975UF Reference Manual page 12

Introduction
June 2021
Sensing elements
The IR sensor in the Rosemount Rosemount 975UF is sensitive to radiation over the range
of 2.5 to 3.0 microns, where the H
detection of hydrocarbon fires, gas fires, hydroxyl, and hydrogen fires, as well as metal and
inorganic fires.
The UV sensor is sensitive to radiation over the range of 0.185 to 0.260 µm. The UV
channel incorporates a special logic circuit that eliminates false alarms caused by solar
radiation and other non-fire UV sources. Furthermore, the UV channel's sensitivity is
stabilized over the working temperature range.
Detection levels
Simultaneous detection of radiation in both the UV and the IR channels having an intensity
that exceeds the detector's preset warning level results in a Warning signal.
Simultaneous detection of radiation in both the UV and the IR channels having an intensity
that exceeds the detector's preset alarm levels results in an Alarm signal.
Simultaneous detection of radiation in both the UV and the IR channels having an intensity
that exceeds the detector's preset flash-fire detection level results in an immediate Alarm
signal.
As the present dual range and level of radiation as well as the flickering pattern are
characteristics of real fire, all other radiation sources apart from actual fire are not
detected, thus avoiding false alarms.
1.4.2 Heated optics
The flame detector uses heated optics. The heater increases the temperature of the
optical surface by 5 to 8 °F (3 to 5 °C) above the ambient temperature to improve
performance in icing, condensation, and snow conditions.
The heated optics can be set to one of the following:
• Off, not operating.
• On continuously.
• Automatic, per temperature change (default): the operator can define the start
temperature below which the window is heated. The default is 41 °F (5 °C). The
operator can define this temperature between 32 °F (0 °C) and 122 °F (50 °C). The
heating stops when the temperature is 27 °F (15 °C) above the start temperature.
For more information, see
1.4.3 HART
The flame detector uses the HART protocol.
HART communication is a bi-directional industrial field communication protocol used to
communicate between intelligent field instruments and host systems. HART is the global
standard for smart process instrumentation, and the majority of smart field devices
installed in plants worldwide are HART-enabled. HART is available in output configurations
1A, 2A, and 3A (see
12
Configure the
®
protocol
Output configuration).
emission has a unique spectral peak that enables
2
detector.
Reference Manual
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