Rosemount 975 Flame Detector, Emerson Triple IR (IR3) and UV/IR Flame Detector

What is the Rosemount 975 flame detector?

The Rosemount 975 is an Emerson flame detector for industrial hazardous areas: it recognizes the radiation of a fire in its field of view and switches alarm outputs. It comes in two sensing families. The 975MR and 975HR use QuadSense triple infrared (IR3), which watches four infrared bands; the 975UF and 975UR use UV/IR, a dual sensor whose ultraviolet and infrared channels can work separately or combined. Detection behavior is adjusted through configuration parameters over RS-485 Modbus or HART.

Every version has two-mode heated optics, a continuous built-in test and an event log. Emerson lists the 975 as active, with 150,000 hours MTBF and a five-year warranty.

Selection note: Pick the version by the fire you expect. 975MR: IR3 for hydrocarbon fires. 975HR: IR3 with hydrogen fire detection. 975UF: UV/IR with hydrogen fire detection. 975UR: UV/IR without it. Emerson notes that hydrogen fire detection exists only on the 975HR and 975UF, that silane fire is listed for the 975UF only, and that ammonia fire is covered by the 975HR, 975UF and 975UR but not the 975MR.

What are the Rosemount 975 specifications?

Spectral response	975MR: 4 μm to 5 μm; 975HR: 2 μm to 5 μm (four IR bands each); 975UF and 975UR: UV 0.185 to 0.260 μm plus IR 2.5 to 3.0 μm (UF) or 4.3 to 4.8 μm (UR)
Detection range (1 ft² (0.1 m²) pan fire, highest sensitivity)	Gasoline or n-heptane: IR3 300 ft. (90 m), UV/IR 93 ft. (28 m); methane or LPG: IR3 207 ft. (63 m), UV/IR 60 ft. (18 m)
Response time, IR3	Typically < 2 s at 131 ft. (40 m), 10 s at 300 ft. (90 m); ultra-fast typically < 1 s at 100 ft. (30 m)
Response time, UV/IR	Typically 5 s at 93 ft. (28 m); ultra-fast 20 ms for flash fire pan fire from 10 ft. (3 m), via analog voltage output
Explosion response, all	50 ms for a 1 ft. (0.3 m) LPG/air sphere, at 66 ft. (20 m) for IR3 and 32.8 ft. (10 m) for UV/IR
Sensitivity ranges	IR3: six; UV/IR: three
Field of view	975MR, 975UF, 975UR: horizontal 100°, vertical 95°; 975HR: 90° x 90° for hydrogen, 80° x 80° for other fuels
Operating voltage	24 Vdc nominal (18 to 32 Vdc)
Power at 24 Vdc	IR3: 60 mA, 1.4 W (no heater) to 280 mA, 7.6 W (heater and alarm); UV/IR: 100 mA, 2.2 W to 320 mA, 7.7 W
Relays	Alarm, fault, and auxiliary; SPDT volt-free contacts rated 2 A at 30 Vdc
Communication	HART (FSK) on the 0-20 mA loop; RS-485 Modbus-compatible link
Cable entries	2 x ¾-in.-14 NPT conduits or 2 x M25 x 1.5 mm ISO
Temperature range	Operating and storage: -76 to +185 °F (-60 to +85 °C)
Humidity	Non-condensing relative humidity up to 100%
Enclosure	Electropolished stainless steel 316, or copper-free aluminum (less than 1%), polyurethane painted; 4 x 4.6 x 6.18 in. (100.6 x 117 x 155 mm)
Weight	Stainless steel: 6.3 lb. (2.9 kg); aluminum: 2.8 lb. (1.3 kg); tilt mount: 2.5 lb. (1.1 kg)
Water and dust	IP66 and IP68 per EN60529; NEMA 250 6P; environmental standard DNV 2-4
Reliability and warranty	150,000 hours MTBF; five-year warranty

Selection note: Range and speed trade against each other between the two families. On the same 1 ft² gasoline pan fire, the IR3 versions see 300 ft. (90 m) and the UV/IR versions 93 ft. (28 m), but only the UV/IR versions list the 20 ms ultra-fast response on a flash fire at 10 ft. (3 m). The IR3 versions also offer six sensitivity ranges against three, and draw less current without the heater (60 mA against 100 mA).

Where is the Rosemount 975 used, and when is another Emerson model the better fit?

Emerson’s 975 application list runs from onshore and offshore oil and gas, refining, chemical and petrochemical plants, tank farms and power generation to hydrogen uses (fuel cell plants, hydrogenation, battery charging stations) and to explosives, fertilizer, aerospace, pharmaceutical, food, mining and warehouse sites.

A flame detector reports a fire that is already burning. Emerson’s Incus data sheet describes point gas, ultrasonic and optical flame detectors as one safety system, so for early warning look at the Rosemount 625IR point gas detector, the Rosemount 935 open path detector and the Rosemount Incus ultrasonic leak detector.

Emerson also sells the Spectrex 40/40D flame detector: its data sheet lists the same four detection choices as the 975 (40/40D-I, 40/40D-M, 40/40D-LB and 40/40D-L4B) and the same headline range of up to 300 ft. (90 m), useful where a specification names Spectrex. More background: PE Energy flame detector selection guide.

Selection note: Hydrogen is where the two hydrogen-capable versions part ways. On Emerson’s hydrogen test, a plume fire 30 in. (0.75 m) high and 10 in. (0.25 m) wide, the 975HR detects at 164 ft. (50 m) and the 975UF at 70 ft. (21 m). On an ammonia fire, the 975HR reaches 117 ft. (35 m), the 975UF 30 ft. (9 m) and the 975UR 17.5 ft. (5 m). Silane fire is listed only for the 975UF, at 67 ft. (20 m).

Which approvals, outputs and documents apply to the Rosemount 975?

The 975 ordering table lists these product certification codes:

A1	ATEX/IECEx/UKCA Flameproof
A2	USA and Canada Explosion-Proof (aluminum enclosure: FM, FMC; stainless steel enclosure: FM, FMC, CSA US/C)
E2	INMETRO Flameproof
E3	China Flameproof and CCCF
EM	Technical Regulations Customs Union (EAC) Flameproof

Emerson describes the 975 as SIL3 compatible. Water and dust protection is IP66 and IP68 per EN60529 and NEMA 250 6P, and the environmental standard is DNV 2-4. Full approval data sits in Emerson’s separate Rosemount 975 Series Certification Information.

Outputs on every version: three relays (alarm, fault, auxiliary), a configurable 0-20 mA stepped output with HART, and RS-485 Modbus, all on universal wiring (code 4U).

Documents: Rosemount 975 data sheet, March 2026, MS-00813-0500-4974 Rev AB and the Rosemount 975 page on Emerson.com.

Maintenance note: The stepped 0-20 mA output tells the control system why a detector is not in its normal state: 0 ± 1 mA is a fault, 2 mA ± 0.3 mA a built-in test (BIT) fault, 4 mA normal, 16 mA warning and 20 mA alarm.

How do I request a quote for the Rosemount 975?

Emerson sells the 975 as a detector (PN 975XXXXXXXXX) plus separate accessories. Send PE Energy the full model code, or one choice from each field of the ordering table:

Measurement type	MR IR3; HR IR3 with hydrogen fire detection; UF UV/IR with hydrogen fire detection; UR UV/IR
Output	4U Universal wiring
Housing style	6A aluminum, ¾-in. NPT; 8A aluminum, M25; 6S stainless steel, ¾-in. NPT; 8S stainless steel, M25
Temperature rating	3: -76 to +185 °F (-60 to +85 °C)
Product certification	A1, A2, E2, E3 or EM
Tilt mount	Y tilt mount; N no tilt mount
Protective cover	7 ABS plastic; 8 stainless steel 316
Special option	H Enhanced hot CO2 discrimination (975MR only)

Accessories Emerson lists by part number:

FS-IR-975 / FS-HR-975 / FS-UVIR-975	Flame simulators (ex-proof) for 975MR / 975HR / 975UF and 975UR models
877090	Tilt mount
877670	Flame detector duct mount assembly
789260-2 / 789260-1 / 789260-3	Pole mount assembly, 2 in. / 3 in. / 4 in.
877650 / 877563	Air shield assembly / field of view limiter
877263 / 877163	Protective cover, plastic / stainless steel

Add quantity. PE Energy confirms price, availability and lead time with the quote. Request a Rosemount 975 quote from PE Energy.

Selection note: The H option (enhanced hot CO2 discrimination) is available for the 975MR only, and each flame simulator fits one detection type, so name the measurement type before adding either. A tilt mount adds 2.5 lb. (1.1 kg).

How do I test a Rosemount 975 flame detector without an open flame?

Use the Rosemount Flame Simulator, which Emerson offers in three models to back up the 975’s own self-test. It gives off UV and/or IR radiation in a pattern the detector reads as fire, so a technician can trip the outputs, check the loop to the control system and confirm the window is clean, without a real flame. It is handheld and battery powered and works from floor or deck level, with no scaffolding or ladders, even in classified areas (Zones 1 and 2). See the Rosemount Flame Simulator page.

Maintenance note: Emerson gives the simulator activation range as up to 40 ft (12 m) for the FS-HR-975 and FS-IR-975, and 20 ft (6 m) for the FS-UVIR-975; one charge covers at least 1,000 tests. Between simulator tests, the 975’s built-in test runs continuously and flags a BIT fault at 2 mA.