Rosemount™ 625ND Infrared Combustible Gas Sensor

The Rosemount 625ND Infrared Combustible Gas Sensor provides accurate, low-maintenance detection of hydrocarbon gases using non-dispersive infrared technology. Designed for use with the Rosemount 925 Fixed Gas Detector, the Rosemount 625ND measures combustible gas concentrations from 0–100% LEL, helping industrial facilities monitor for flammable gas leaks before they become a greater safety risk.

Built for demanding process environments, the Rosemount 625ND supports the detection of common hydrocarbon gases such as methane, ethane, propane, ethylene, and butane. Its smart sensor design stores configuration, calibration, and gas-sensing data directly within the sensor module, allowing it to communicate digitally with the Rosemount 925 transmitter for stable readings, diagnostics, and simplified maintenance.

For facilities in oil and gas, refining, petrochemical processing, power generation, LNG, and other hazardous industrial environments, the Rosemount 625ND offers a reliable solution for fixed combustible gas detection. With fast response times, rugged construction, hazardous area approvals, and flexible direct or remote mounting options, it is well suited for both new gas detection systems and replacement sensor applications. Westech Industrial offers product support, service capabilities, and custom fabrication options to help customers integrate Rosemount gas detection solutions into their facility’s safety systems.

Rosemount™ 625ND Infrared Combustible Gas Sensor
Rosemount™ 625ND Infrared Combustible Gas Sensor - Image 2

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Description

Non-Dispersive Infrared Detection for Hydrocarbon Gases

The Rosemount 625ND uses non-dispersive infrared sensing technology to measure combustible hydrocarbon gases through infrared absorption. This makes it a strong choice for fixed %LEL gas detection applications where stable performance and low maintenance are important.

Smart Sensor Module Design

The Rosemount 625ND is a smart sensor module that retains its own configuration settings, calibration information, and gas-sensing data. When connected to the Rosemount 925 transmitter, this information is communicated digitally to support reliable detection, diagnostics, and simplified replacement.

Fast Response for Combustible Gas Monitoring

The sensor provides fast response times for methane, propane, ethylene, n-butane, and ethane, supporting early warning in applications where combustible gas leaks must be detected quickly.

Pre-Calibrated and Field-Ready

Rosemount 625ND sensors can be pre-calibrated for target gases, helping reduce commissioning time in the field. In addition to field calibration, sensors can also be calibrated off-site and installed later, which can help minimize downtime during maintenance or sensor replacement.

Digital Communication with the Rosemount 925 Transmitter

When paired with the Rosemount 925 transmitter, the sensor and transmitter continuously communicate digitally. The transmitter provides 4–20 mA output with HART® 7 protocol, relays, alarm outputs, fault indication, and a local operator interface for real-time readings, alerts, and diagnostic information.

Designed for Harsh Industrial Environments

The Rosemount 625ND is designed for challenging operating conditions, with a standard operating temperature range of -40 to +70 °C and humidity tolerance from 0–95% relative humidity, non-condensing. The sensor is available with aluminum or stainless steel housing options and achieves NEMA 4X and IP66 enclosure ratings when properly installed.

Flexible Direct or Remote Mounting

The Rosemount 625ND can be installed directly on the Rosemount 925 transmitter or mounted remotely using the Rosemount 905 Junction Box. Remote mounting allows the sensor to be installed where gas detection is required while keeping the transmitter in a more accessible location for viewing, configuration, and maintenance.

Hazardous Area and Safety Certifications

The Rosemount 625ND and Rosemount 925FGD system are designed for hazardous industrial environments, with global hazardous area certification options and SIL2 functional safety certification available for applications where safety system integrity is a key requirement.

Applications

The Rosemount 625ND Infrared Combustible Gas Sensor is ideal for fixed gas detection applications where hydrocarbon gas leaks may create a combustible atmosphere. Typical applications include oil and gas production sites, refineries, petrochemical facilities, LNG facilities, gas processing plants, compressor stations, power generation facilities, loading terminals, chemical processing areas, fuel storage areas, and other hazardous industrial environments requiring continuous %LEL combustible gas monitoring.

It is especially useful in applications where facilities need low-maintenance combustible gas detection, reliable hydrocarbon gas measurement, remote sensor placement, and integration with site alarm systems or control systems through the Rosemount 925 transmitter.

Documents

rosemount-925fgd-brochure-en-May2025_Westech.pdf

rosemount-925fgd-data-sheet-en-May2025_Westech.pdf

rosemount-925fgd-configuration-data-sheet_May2025_Westech.pdf

rosemount-925fgd-manual-en-May2025_Westech.pdf

Manufacturer info

Emerson concentrates on the most complex and profound challenges facing the world in the process, industrial, commercial and residential markets. We refocused our business portfolio to deliver solutions that bring greater value to our customers. Learn how we’ve transformed and why.

https://www.emerson.com

SPECS

Measurement type:
Hydrocarbon gas concentration monitoring from 0–100% Lower Explosive Limit (LEL).
Sensor type:
Rosemount 625 Non-Dispersive Infrared Sensor.
Compatible transmitter:
Rosemount 925 Fixed Gas Detector transmitter.
Compatible system:
Rosemount 925FGD Fixed Gas Detector.
Gas detection technology:
Non-dispersive infrared detection for combustible hydrocarbon gases.
Common target gases:
Methane, ethane, propane, ethylene, n-butane, and other applicable hydrocarbon combustible gases depending on calibration and site requirements.
Factory calibration options:
Default methane calibration, with available factory calibration options for ethane, propane, butane, and ethylene.
Outputs when paired with the Rosemount 925 transmitter:
4–20 mA with HART® 7 protocol and relays.
Local interface when paired with the Rosemount 925 transmitter:
Local Operator Interface display for primary variable information, alert status, diagnostics, calibration, and maintenance activities.
Response time:
For methane, propane, ethylene, n-butane, and ethane, T50 is less than 7 seconds and T90 is less than 10 seconds.
Accuracy:
Gas accuracy is ±3% LEL below 50% LEL and ±5% LEL above 50% LEL.
Repeatability:
Rosemount 625ND repeatability is ±0.75% from 0–50% LEL and ±1.25% from 50–100% LEL.
4–20 mA accuracy:
0.1% of span when used with the Rosemount 925FGD system.
Humidity limits:
0–95% relative humidity, non-condensing.
Standard operating temperature:
-40 to +158 °F (-40 to +70 °C).
Storage temperature:
-40 to +167 °F (-40 to +75 °C).
Input power requirements when used with the Rosemount 925 transmitter:
18 to 30 Vdc.
Maximum power consumption:
2.4 W with heater off.
Housing materials:
Low-copper aluminum or stainless steel.
Enclosure rating:
NEMA 4X and IP66 when properly installed with the required ingress protection filter.
Remote mounting:
Sensor can be mounted remotely from the transmitter with separation up to 1,500 ft (457 m) using the Rosemount 905 Junction Box.
Available certifications:
ATEX/UKEX flameproof, ATEX/UKEX dust, ATEX/UKEX flameproof and dust, IECEx flameproof and dust, US explosion-proof and dust ignition-proof, Canada explosion-proof and dust ignition-proof, with SIL2 safety certification available for the Rosemount 925FGD system.
Available regions through Westech Industrial:
BC, AB, and SK.

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PRODUCT FAQ's

What does the Rosemount 625ND Infrared Combustible Gas Sensor detect?
The Rosemount 625ND detects combustible hydrocarbon gases in the 0–100% LEL range. It is commonly used for methane, ethane, propane, ethylene, and butane detection in industrial environments where flammable gas monitoring is required.
How does the Rosemount 625ND work?
The Rosemount 625ND uses non-dispersive infrared technology to detect combustible hydrocarbon gases. Gas must physically pass through the sensor’s ingress protection filter and sinter to reach the sensing element, making proper placement, orientation, and maintenance important for reliable detection.
Is the Rosemount 625ND a standalone gas detector?
The Rosemount 625ND is the sensor module. It is designed to work with the Rosemount 925 transmitter as part of the Rosemount 925FGD Fixed Gas Detector system. The transmitter provides the local display, outputs, relays, HART communication, alerts, and diagnostics.
Can the Rosemount 625ND be mounted remotely?
Yes. The Rosemount 625ND can be mounted directly to the Rosemount 925 transmitter or remotely using the Rosemount 905 Junction Box. Remote mounting allows the sensor to be placed closer to the likely gas source while keeping the transmitter more accessible for operators.
Why is proper sensor placement important?
Proper placement helps ensure the sensor is located where gas is most likely to accumulate. Methane and natural gas are lighter than air and tend to rise, while propane and butane are heavier than air and tend to settle lower. Westech Industrial can help review your application and support sensor placement considerations as part of a broader gas detection strategy.
Does the Rosemount 625ND require regular calibration?
Yes. While the Rosemount 625ND is designed for low-maintenance operation, calibration should still be performed according to the site’s safety requirements and manufacturer guidance. Emerson notes a minimum recommended calibration interval of 12 months, with more frequent calibration recommended where environmental conditions vary significantly.
Can Westech Industrial help with Rosemount 625ND product selection?
Yes. Westech Industrial can help customers in BC, Alberta, and Saskatchewan select the right Rosemount 625ND configuration based on the target gas, mounting requirements, certification needs, operating environment, and integration requirements.
Does Westech Industrial provide service support for gas detection systems?
Yes. Westech Industrial provides support for industrial gas detection solutions, including product selection, commissioning support, troubleshooting, maintenance guidance, and service support. Our team can also help with replacement sensors, calibration accessories, and system upgrades where required.
Can Westech Industrial integrate the Rosemount 625ND into a custom gas detection system?
Yes. Westech Industrial offers custom fabrication and integration capabilities for industrial safety and gas detection applications. Depending on the project requirements, our team can support custom panels, detector assemblies, mounting solutions, wiring considerations, and integration with broader fire and gas detection systems.
Why choose Westech Industrial for Rosemount combustible gas detection solutions?
Westech Industrial combines product knowledge, regional support, service capabilities, and custom fabrication experience to help customers build practical fixed gas detection solutions. Whether you need a replacement Rosemount 625ND sensor, a complete Rosemount 925FGD system, or support integrating gas detection into a larger safety system, Westech can help match the equipment to the application.