Rosemount™ 935 Open Path Combustible Gas Detector

The Rosemount 935 Open Path Combustible Gas Detector is designed for continuous monitoring of combustible hydrocarbon gases across large areas where a point detector may not provide enough coverage. Using xenon flash infrared transmitter and receiver technology, the Rosemount 935 provides fast, reliable open path gas detection over distances up to 660 ft. (200 m), making it well suited for refineries, tank farms, compressor stations, loading areas, offshore platforms, LNG/LPG facilities, and other hazardous industrial environments.

Built for challenging field conditions, the Rosemount 935 is engineered to maintain reliable performance in environments affected by dust, fog, rain, snow, vibration, condensation, icing, solar radiation, hydrocarbon flames, and other external infrared sources. Its automatic gain control helps maintain accurate detection with up to 95 percent signal obscuration, while heated optics help reduce condensation and ice buildup on the optical window.

The detector provides a high-speed response in under two seconds, high false alarm immunity, continuous self-diagnostics, and an RTC event recorder that stores the last 375 events. The Rosemount 935 is also field configurable using HART® or RS-485 Modbus®, supporting easier commissioning, maintenance, and asset management.

Available at Westech Industrial in BC, AB, and SK, the Rosemount 935 can be supported by Westech’s experienced team. Westech can also assist with custom fabrication requirements, including detector mounting, panel integration, system design support, and gas detection solutions built for demanding Canadian industrial environments.

Rosemount™ 935 Open Path Combustible Gas Detector

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Description

Long-Range Open Path Gas Detection

The Rosemount 935 open path gas detector monitors combustible hydrocarbon gases across large industrial areas. Depending on the selected transmitter range, it supports installation distances from 23 to 660 ft (7 to 200 m), giving facilities flexible coverage options. As a result, operators can monitor wider zones with one transmitter and receiver pair.

Fast Response for Combustible Gas Hazards

The Rosemount 935 responds to combustible gas hazards in less than two seconds. This fast response helps facilities identify potential leaks quickly. Therefore, operators can take action before gas hazards continue to develop. This response time supports critical safety monitoring in high-risk process areas.

High False Alarm Immunity

Industrial environments often include sunlight, heat, flames, vibration, and other background conditions. However, the Rosemount 935 offers strong false alarm immunity. It is not influenced by solar radiation, hydrocarbon flames, or other external infrared radiation sources. As a result, facilities can reduce nuisance alarms and improve operator confidence.

Reliable Performance in Harsh Weather

The Rosemount 935 performs reliably in demanding outdoor and process environments. Heated optics help eliminate condensation and icing on the detector window. In addition, automatic gain control supports accurate detection during dust, fog, rain, snow, or heavy obscuration. The detector can continue operating with up to 95 percent signal obscuration.

Continuous Device Health Monitoring

Built-in self-test functionality continuously monitors device health. This feature helps operators identify potential faults before they affect performance. In turn, maintenance teams can respond faster and plan service more effectively. Continuous diagnostics also help improve confidence in the overall gas detection system.

Event Recording for Maintenance Review

The Rosemount 935 includes an RTC event recorder. It stores the last 375 events for maintenance and troubleshooting review. This information can help teams understand alarm history, fault activity, and operating conditions. As a result, facilities can support better maintenance decisions over time.

Field Configurable Communication Options

The detector supports field configuration through HART® or RS-485 Modbus®. These communication options help simplify commissioning, diagnostics, and ongoing maintenance. In addition, the RS-485 interface provides data communication to a PC or handheld unit. This flexibility helps facilities integrate the detector into broader control and safety systems.

Rugged Stainless Steel Construction

The source and detector housings use 316L stainless steel with an electro-polished finish. This rugged construction supports reliable operation in harsh industrial locations. Additionally, the circuit boards are conformal coated and protected from mechanical vibration. This design helps the detector withstand demanding site conditions.

Visual Status Indicators

The receiver includes front and back visual status indicators. Three-colour LEDs show power, fault, and alarm status. Green indicates power on, amber indicates fault, and red indicates alarm. Therefore, operators can quickly check detector status in the field.

Hazardous Area and Functional Safety Approvals

The Rosemount 935 includes approvals for demanding hazardous area applications. Approvals include ATEX, IECEx, FM/FMC, TR CU (EAC), INMETRO, and SIL-2 TÜV certification. These approvals support use in many industrial safety applications.

Applications

The Rosemount 935 Open Path Combustible Gas Detector is ideal for industrial facilities that need to monitor large hazardous areas for combustible hydrocarbon gas leaks. It is especially useful in applications where gas may disperse over open spaces, around process equipment, or between storage and loading areas.

Common applications include:

  • Petrochemical, pharmaceutical, and chemical storage and production areas
  • Flammable chemical storage sites and hazardous waste disposal areas
  • Refineries, oil platforms, pipelines, refuelling stations, and fuel storage facilities
  • Hazardous loading docks, transportation depots, and shipping warehouses
  • Engine rooms and enclosed industrial equipment areas
  • Compressor and pumping stations
  • Test cells
  • LNG and LPG systems
  • Offshore FPSO facilities and fixed oil rigs
  • Canadian oil and gas, energy, and industrial safety applications in BC, AB, and SK

Documents

Rosemount_935 Open Path Combustible Gas Detector_Data Sheet_May2026_Westech.pdf

Emerson_Rosemount 935/936_Safety Brochure_May2026_Westech.pdf

Manufacturer info

Emerson has boldly transformed itself to create value for our customers and shareholders. With our newly energized focus on our two core business platforms — Automation Solutions and Commercial & Residential Solutions — we can confront the challenges of an increasingly complex and unpredictable marketplace from a position of strength. This allows us to drive both near- and long-term value. And retain our single-trusted-partner status with the process, industrial, commercial and residential industries.

https://www.emerson.com/

SPECS

Product:
Rosemount 935 Open Path Combustible Gas Detector.
Detection Type:
Open path combustible hydrocarbon gas detection.
Detected Gas:
C1-C8 selective gases.
Common Hydrocarbon Gas Applications:
Methane, ethylene, propane, ethane, and butane.
Detection Technology:
Xenon flash infrared transmitter and receiver.
Maximum Detection Range:
660 ft. (200 m).
Installation Distance, T1 Source:
23 to 66 ft. (7 to 20 m).
Installation Distance, T2 Source:
50 to 132 ft. (15 to 40 m).
Installation Distance, T3 Source:
115 to 330 ft. (35 to 100 m).
Installation Distance, T4 Source:
265 to 660 ft. (80 to 200 m).
Response Time:
Less than 2 seconds.
Sensitivity Range:
0 to 5 LEL.m methane and propane; 0 to 8 LEL.m ethylene.
Minimum Detectable Level:
0.15 LEL.m.
Accuracy:
±7.5 percent of the reading or ±4 percent of full scale, whichever is greater.
Displacement / Misalignment Tolerance:
±0.5 degrees.
False Alarm Immunity:
Not influenced by solar radiation, hydrocarbon flames, or other external infrared radiation sources.
Signal Obscuration Performance:
Automatic gain control supports detection in challenging conditions with up to 95 percent signal obscuration.
Event Recording:
RTC event recorder stores the last 375 events.
Operating Temperature:
-67 °F to +149 °F (-55 °C to +65 °C).
Humidity:
Up to 95 percent non-condensing; withstands up to 100 percent relative humidity for short periods.
Heated Optics:
Helps eliminate condensation and icing on the window.
Power Supply:
24 Vdc nominal (18 to 32 Vdc).
Typical Power Consumption:
Detector: 220 mA; Source: 240 mA.
Warm-Up Time:
30 seconds for transmitter and receiver.
Electrical Connection:
Two ¾-in. – 14 NPT conduits or 2 x M25 x 1.5 mm ISO.
0–20 mA Current Output:
Sink (source option) configuration: maximum load of 500 ohm at 18 to 32 Vdc; Gas reading: 4–20 mA; normal zero reading: 4 mA; maintenance call: 3 mA; obscuration / beam block: 2 mA; zero calibration mode: 1 mA; fault: 0 mA.
HART® Protocol:
HART communication on 0–20 mA analog FSK for maintenance and asset management.
RS-485 Modbus® Interface:
Provides complete data information to a PC and receives control commands from a PC or handheld unit.
Visual Status Indicator:
Three-colour LED indicator; green for power on, amber for fault, red for alarm.
Enclosure:
316L stainless steel source and detector housings with electro-polished finish.
Circuit Board Protection:
Conformal coated and protected from mechanical vibration.
Dimensions, Detector / Source:
10.5 x 5.1 x 5.1 in. (267 x 130 x 130 mm).
Dimensions, Tilt Mount:
4.7 x 4.7 x 5.5 in. (120 x 120 x 158 mm).
Weight, Detector / Source:
11 lb. (5 kg).
Weight, Tilt Mount:
4.2 lb. (1.9 kg).
Water and Dust Tight Rating:
IP66 and IP68; NEMA® 250 6P.
IP68 Rating:
Rated for 2 m depth for 45 minutes.
Reliability:
SIL2 per IEC61508, TÜV approved.
Mean Time Between Failures (MTBF):
Above 100,000 hours.
Warranty:
Three years for detector and source.
Approvals:
ATEX, IECEx, FM/FMC, TR CU (EAC), INMETRO, SIL-2 TÜV.
Performance Approvals:
Functional performance certified per FM 6325, EN60079-29-4, and DNV.

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PRODUCT FAQ's

What does the Rosemount 935 Open Path Combustible Gas Detector detect?
The Rosemount 935 is designed to detect combustible hydrocarbon gases using open path infrared technology. It is suitable for C1-C8 selective gases and is commonly used for methane, ethylene, propane, ethane, butane, and other hydrocarbon gas monitoring applications.
How far can the Rosemount 935 detect combustible gas?
The Rosemount 935 can monitor open path distances up to 660 ft. (200 m). The available transmitter ranges support installation distances from 23 to 66 ft. (7 to 20 m), 50 to 132 ft. (15 to 40 m), 115 to 330 ft. (35 to 100 m), and 265 to 660 ft. (80 to 200 m).
Is the Rosemount 935 suitable for harsh outdoor environments?
Yes. The Rosemount 935 is designed for harsh environments affected by dust, fog, rain, snow, vibration, condensation, and icing. Heated optics help keep the window clear, while automatic gain control supports operation with up to 95 percent signal obscuration.
How fast does the Rosemount 935 respond to combustible gas?
The Rosemount 935 has a response time of less than two seconds, supporting fast detection of combustible hydrocarbon gas hazards in industrial environments.
Does the Rosemount 935 help reduce false alarms?
Yes. The detector has high false alarm immunity and is not influenced by solar radiation, hydrocarbon flames, or other external infrared radiation sources.
Does the Rosemount 935 include event logging?
Yes. The Rosemount 935 includes an RTC event recorder that stores the last 375 events for maintenance review and troubleshooting
What communication options are available?
The Rosemount 935 supports 0–20 mA current output, HART® communication, and RS-485 Modbus® communication. These options support maintenance, asset management, diagnostics, and integration with control systems.
What hazardous area approvals does the Rosemount 935 have?
The Rosemount 935 includes approvals such as ATEX, IECEx, FM/FMC, TR CU (EAC), INMETRO, and SIL-2 TÜV.
Can Westech Industrial support Rosemount 935 installation and maintenance?
Yes. Westech Industrial can support customers with product selection, application review, commissioning support, troubleshooting, and service for gas detection and life safety systems. Westech’s team can help determine whether the Rosemount 935 is the right fit for the site layout, hazard area, and monitoring requirements.
Can Westech Industrial provide custom fabrication for gas detection systems?
Yes. Westech Industrial can assist with custom fabrication requirements related to gas detection projects, including mounting solutions, detector integration, control panels, system layouts, and fabricated assemblies designed for demanding Canadian industrial environments.