Emerson Rosemount 936, Reference Manual

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• Fast connections to intrinsically safe (I.S.) approved hand-held diagnostic/calibration
unit
• Three-year warranty
2.2 Applications
You can use the Rosemount 936 system to monitor toxic gas concentrations in various
applications, such as:
• Petrochemical, pharmaceutical, and other chemical storage and production areas
• Toxic chemical storage sites and hazardous waste disposal areas
• Detecting H
2
S in desulfurization processes at refineries, oil platforms, pipelines,
refueling stations, and fuel storage facilities
• Transportation depots and shipping warehouses of degreasing and cleaning solvents
• Styrene monomer, polymers, and plastic industries
• NH
3
production facilities, storage, and transportation
• Air conditioning, refrigeration, and agriculture application areas for NH
3
and
derivatives
• Semiconductor industry in which NH
3
concentration monitoring is required
2.3 Principle of operation
The system detects gases through dual-spectral range monitoring, analyzing the
absorption of radiation caused by gases in the atmosphere and comparing it (ratio) to
background atmospheric absorption.
2.3.1 Spectral fingerprint
Each hazardous material is detected at a specific wavelength selected according to its
specific spectral absorption or
fingerprint .
The detection process involves two separate sensors, one that absorbs a particular gas and
one that is not sensitive to it.
2.3.2 Optical path
The Rosemount 936 detects the presence of toxic airborne vapors, gases, or aerosols in a
monitored area when the defined substance crosses/enters the optical path between the
radiation source unit and the detector.
Toxic gases/vapors present in the atmosphere cause absorption of the radiation pulse at
specific wavelengths in the optical path between the radiating source and the detector.
This causes a change in the signal intensity received by the detector, which is translated
into an output related to the detector's measurement scale.
The system analyzes the defined open path at the spectral bands specific to the materials
being monitored. The automatic gain control (AGC) unit compensates for environmental
Technical description Reference Manual
October 2021 00809-0100-4036
10 Emerson.com/Rosemount