Rosemount 925FGD Fixed Gas Detector, Emerson 925 Gas Detection Transmitter with 625ND NDIR Sensor

What is the Rosemount 925FGD fixed gas detector, and how does it relate to the Rosemount 925?

The Rosemount 925FGD is Emerson’s fixed combustible gas detector: a Rosemount 925 Gas Detection Transmitter combined with a Rosemount 625 Gas Detection Sensor (the 625ND NDIR sensor). It measures hydrocarbon gases from 0 to 100% LEL and reports through 4-20 mA with HART 7 and relays. Emerson designs it to be ordered fully assembled and ready to install, with one model code that covers both the transmitter and the sensor options.

The Rosemount 925 is the transmitter half of that system. Emerson also sells it on its own ordering table, as it does the 625 sensor and the Rosemount 905 junction box used when the transmitter is mounted remote from the sensor. Emerson describes the 925FGD as its first ground-up development for fixed combustible gas detection, and lists both the 925 transmitter and the 925FGD as active.

Replacement note: Which ordering table to use depends on what is missing on site. A new detection point is a 925FGD. A failed transmitter can be replaced with a 925 alone, down to electronics only: housing code E4 (no housing, replacement transmitter electronics only) must go with certification code TE (no approvals, replacement transmitter electronics only). A spare or pre-calibrated sensor is a 625 ordered standalone, and a 905 junction box can also be ordered on its own.

What are the Rosemount 925FGD specifications?

Measurement	Hydrocarbon gases: 0-100% Lower Explosive Limit (LEL)
Sensor type	Rosemount 625 Non-Dispersive Infrared Sensor
Outputs	4-20 mA with HART 7 protocol, relays
Local operator interface	Integral LOI display shows alert state and diagnostic information
Response time	T50 < 7 sec, T90 < 10 sec (methane, propane, ethylene, n-butane, and ethane)
Gas accuracy	±3 percent LEL < 50 percent LEL; ±5 percent LEL > 50 percent LEL
4-20 mA accuracy	0.1 percent of span
Repeatability (625ND)	±0.75 percent from 0-50 percent LEL; ±1.25 percent from 50-100 percent LEL
Power supply	18 to 30 Vdc; maximum power consumption 2.4 W with heater off
Operating temperature	Standard: -40 to +158 °F (-40 to +70 °C); transmitter only with heater on: -67 to +167 °F (-55 to +75 °C)
Storage temperature	-40 to 167 °F (-40 to +75 °C)
Humidity	0-95 percent relative humidity, non-condensing
Materials	Low-copper aluminum or stainless steel housing; polyurethane paint; Buna-N cover O-ring
Enclosure rating	NEMA 4X and IP66
EMC / vibration	EN 50270:2015 and NE21; vibration tested per IEC 60079-29 and IACS E10
Weight	925 transmitter: 6.3 lb (2.9 kg) aluminum, 11.1 lb (5.1 kg) SST; 625ND sensor: 1.3 lb (0.6 kg) aluminum, 2.7 lb (1.2 kg) SST; 905 junction box: 2.7 lb (1.2 kg) aluminum, 5.9 lb (2.7 kg) SST
Warranty	925 transmitter and 625ND sensor: three-year limited each

Selection note: Housing material changes the weight: a 925 transmitter is 6.3 lb (2.9 kg) in aluminum and 11.1 lb (5.1 kg) in stainless steel. For cold sites, Emerson rates the transmitter alone from -67 to +167 °F (-55 to +75 °C) with the heater on, against -40 to +158 °F (-40 to +70 °C) for the standard detector, so check where the sensor will sit as well as the transmitter.

Where is the Rosemount 925FGD used, and when is another Emerson model the better fit?

Emerson positions the 925FGD for early combustible gas leak detection in industrial processes and hazardous areas, tied into the plant safety system. Its NDIR sensing resists poisoning and drift and works without oxygen, which Emerson calls well suited for harsh and inert environments, and the low-maintenance design targets points that are hard to access. The smart sensor also fits sites that prefer to calibrate sensors off-site and swap them during planned service.

Other Emerson detectors in this range fit other needs:

• Wireless instead of wired: the Rosemount 928 wireless gas monitor needs no power or signal cable, using a Rosemount 628 sensor and an intrinsically safe power module.
• A single stainless detector with no field calibration: the Rosemount 625IR.
• A line of sight instead of a point: the Rosemount 935 open path combustible gas detector.
• Pressurized leaks of any gas outdoors: the Rosemount Incus ultrasonic gas leak detector.

Selection note: 925FGD wired against 928 wireless, from Emerson’s data sheets. 925FGD: 18 to 30 Vdc supply, maximum 2.4 W with heater off, T90 < 10 sec, operating -40 to +158 °F (-40 to +70 °C), 4-20 mA with HART 7 and relays. 928 with the 628 combustible sensor: lithium-thionyl chloride power module, T90 < 24 seconds, ±3 % LEL on methane, operating -40 to +122 °F (-40 to +50 °C), WirelessHART output with an optional discrete output.

Which approvals, outputs and documents apply to the Rosemount 925FGD and 925?

The 925FGD and the standalone 925 share these certification codes, printed as Emerson words them:

E1	ATEX/UKEX flameproof
ND	ATEX/UKEX dust
K1	ATEX/UKEX flameproof and dust
E7	IECEx flameproof and dust
E5	US explosion-proof and dust ignition-proof
E6	Canada explosion-proof and dust ignition-proof
TE (925 only)	No approvals, replacement transmitter electronics only

Emerson states the 925FGD is certified to SIL2 functional safety standards; option QT adds the safety certification for IEC 61508 (SIL2 certificate) and Q4 a calibration certificate. Outputs are 4-20 mA with HART 7 protocol and relays (detector configuration code 1: analog, HART, relays).

Documents: Rosemount 925FGD data sheet, July 2024, 00813-0100-4925 Rev AD, which also holds the 925, 625 and 905 ordering tables. Emerson pages: Rosemount 925FGD and Rosemount 925 transmitter. Background on detector types: PE Energy gas detection systems guide.

Maintenance note: Emerson sets a limit for use outside the safety role: the 925FGD is a safety device, and when it is used as an environmental monitor with percent LEL converted to ppm, readings under 5,000 ppm should be disregarded. Routine calibration and maintenance can be done from the local operator interface, without additional tools or communicators.

How do I request a quote for the Rosemount 925FGD or 925 transmitter?

Send PE Energy the full Emerson model code if you have it. For a complete 925FGD detector, the ordering table asks for:

Model	925FGD Fixed gas detector system
Detector configuration	1 Analog, HART, relays
Sensor technology	NS NDIR for hydrocarbon gases, stainless steel; NA NDIR for hydrocarbon gases, aluminum
Gas type and range	F14 Hydrocarbon gases 0-100% LEL, default methane
Housing and mounting	Direct mount: A1 or S1 (¾-in. NPT), A2 or S2 (M25). Remote mount: A3 or S3 (3/4-in. NPT), A4 or S4 (M25). A = aluminum, S = stainless steel
Product certification	E1, ND, K1, E7, E5 or E6
Factory calibration gas	G01 Ethane, G02 Propane, G03 Butane, G04 Ethylene (methane by default)
Other options	IEC calibration (NFPA is default); BP 2-in. pole mount kit for the transmitter; BB pole mount kit for the 905 junction box; C1 custom software configuration; Q4 calibration certificate; QT SIL2 certificate

For a 925 transmitter alone, the fields are 925, transmitter output 1, channel configuration 1 (single sensor input), housing A1, S1, A2, S2 or E4, a certification code (TE for electronics only), and the BP and C1 options. Add quantity. PE Energy confirms price, availability and lead time with the quote. Request a Rosemount 925FGD or 925 quote from PE Energy.

Model code structure: The sample code in Emerson’s data sheet is not reproduced in its text, so here are the fields in table order for a remote-mounted stainless steel detector for a US site: 925FGD + 1 + NS + F14 + S3 + E5, then options such as G02 for propane calibration and QT for the SIL2 certificate. Remote mount housings (A3, S3, A4, S4) put the sensor away from the transmitter, which is where Emerson uses the Rosemount 905 junction box.