Open-Path Gas Detector Selection Guide: Open Path and Line-of-Sight IR Combustible Gas Detectors for Fence Lines, Compressor Stations and Tank Farms

An open-path gas detector watches a beam instead of a point, so choosing one comes down to path length, fog and beam-block behavior, approvals, outputs, alignment and testing. This guide compares published data for six open-path (line-of-sight) models from Det-Tronics, Honeywell, Dräger, MSA and Teledyne, read on October 14, 2026, and ranks none of them: the right open path infrared combustible gas detector depends on your site.

What is an open-path gas detector (OPGD), and how does it differ from a point IR detector like the PIRECL?

An open-path gas detector (OPGD) is a transmitter and a receiver mounted facing each other, and it detects a hydrocarbon gas cloud that crosses the infrared beam between them. A point IR detector such as the PointWatch Eclipse PIRECL monitors 0 to 100% LFL at the spot where it is mounted, while a line of sight IR gas detector integrates the gas along the whole beam, so a small dense cloud and a large thin cloud can give the same reading. Det-Tronics presents the two as separate layers of protection and recommends line-of-sight detectors for wide open spaces, especially along facility perimeters.

• Different test standards: the PIRECL is performance certified to FM 6310/6320, ANSI/ISA 12.13.01 and CSA C22.2 No. 152, while the LS2000 and Pulsar 7000 cite FM 6325, ANSI/ISA-12.13.04 and EN/IEC 60079-29-4.
• Different speed figures: the PIRECL publishes a methane T90 of 7.1 s (standard) and 1.5 s (fast response) with baffle and no filter, and the FlexSight LS2000 publishes 2 s along the beam.

What does LEL·m (LEL-m, LFL-m) mean, and which measuring range should you specify?

LEL·m is gas concentration, as a fraction of the lower explosive limit, multiplied by the length of cloud the beam crosses: in Det-Tronics’ example, 10 m of cloud at 10% LFL reads 1 LFL-m. The LS2000 and the Searchline Excel Plus and Edge read 0 to 5 LEL·m, the Dräger Pulsar 7000 span can be set from 0 to 4 up to 0 to 8 LEL m, and MSA’s laser Senscient ELDS methane detector adds a 0 to 1 LEL.m range. Specify the range with the alarm points: the LS2000 defaults are 1 LFL-m (low) and 3 LFL-m (high), and Honeywell recommends 1 LEL.m and 3 LEL.m.

Watch the ppm·m conversion: Honeywell equates its recommended 0.5 LEL.m minimum alarm to 22,000 ppm.m of methane, and Det-Tronics calibrates FM/CSA LS2000 variants to ISO/NFPA 497 LFL values and IEC/ATEX variants to IEC values, so use the conversion table for your exact variant. Teledyne publishes a minimal detectable gas level of 0.15 LEL.m for the SafEye.

What path length does an open-path gas detector need for a fenceline, compressor station or tank farm?

An open-path gas detector needs a range band that brackets the real transmitter-to-receiver distance on your fence line, compressor station or tank farm, because most models are sold in path-length bands rather than one universal range. At the short end of a band some models need an extra part: the LS2000 requires its supplied range reduction aperture kit at 5 to 15 m on the short-range model and 30 to 40 m on the long-range model. The comparison table below lists every published band.

Edition check on the LS2000: the 2020 spec sheet shows only 5 to 60 m and 30 to 120 m, while the July 2025 LS2000 manual adds 100 to 200 m that is Det-Tronics verified and, for hazardous locations, Canada only (“Hazloc, Canada only”); third-party verification covers 120 m. For longer perimeter runs, Honeywell’s Searchline Excel Edge covers 60 to 330 m.

How fast do open-path gas detectors respond, and what happens in fog or a beam block?

Published T90 times put open-path gas detectors in one speed class: 2 s for the LS2000, under 2 s for the Pulsar 7000 with its digital link, under 3 s for the Searchline Excel Plus, Edge and SafEye, and 3 s or less for the Senscient ELDS. When the beam is blocked, the detector reports beam block and then fault, not a gas reading: the LS2000 declares a beam-block fault after 1 minute by default, the Excel Plus indicates fault after 30 s without signal, and the Pulsar 7000 signals beam block after 10 s and fault after 120 s.

• Test conditions differ: Det-Tronics states the LS2000’s 2 s T90 at 5.0 LFL-m in the spec sheet and at 2.5 LFL-m in the FM appendix.
• A weak signal slows response: Dräger states a t90 under 10 s with the digital link and under 40 s without it at 5% residual signal, for example in fog or with lens contamination.
• Same manufacturer, two messages: Honeywell’s Excel Plus data sheet claims better fog penetration than any other open path detector, while its Plus/Edge manual says Edge detection at extended ranges may be affected by particularly thick fog.
• LS2000 failure modes: heavy fog or a partial obstruction can cause a low signal fault, a deluge or flood puts the unit into beam-block/fault, and the heated optics melt snow or ice only down to about -20 °C.
• Early warning is off by default: the Excel Plus Beam Block Warning delay defaults to 30 s (settable 30 to 600 s), but the warning is disabled in the factory configuration.

Which approvals and SIL scope should an open-path gas detector carry: Class I Division 1, Zone 1, ATEX, IECEx, SIL 2?

Check the hazardous-location marking and the gas performance approval (such as FM 6325, ANSI/ISA-12.13.04 or EN/IEC 60079-29-4) separately, and copy both from the current data sheet or label, because they change with the option and the document edition. For SIL, read the scope: only the LS2000 Safety-Certified version is certified (by exida, to IEC 61508 Ed. 2, single input, low demand) and Det-Tronics identifies it on the label, while Honeywell’s TÜV SÜD certificate rates the Excel Plus and Edge 4-20 mA output SIL 2 and the relay output SIL 1, valid until November 18, 2026.

• Options change the rating: the LS2000 relay version is rated -55 to +65 °C instead of +75 °C, and its FM approved rating is limited to -50 °C because no conduit fittings, cables or cable glands are listed for use below -50 °C in the US.
• Gas groups: Dräger’s example CSA label for the Pulsar 7000 reads Class I, Div. 1, Groups C & D, T6…T5, with no Group B, and the SafEye Ex marking carries IIB+H2 rather than IIC.
• Editions disagree: Honeywell’s Excel Plus data sheet Rev A 1/21 lists IECEx ULD 18.0016X, while the June 2024 technical manual lists DEMKO 20 ATEX 2281X / IECEx UL 20.0009X.
• Proof testing: the Det-Tronics LS2000 safety manual sets a gas response proof test once per year; the table shows each manufacturer’s SIL wording.
• Date check: after November 18, 2026, ask Honeywell for the renewed certificate before relying on its SIL statement.

Which outputs should an open path detector give your control system?

Every open path detector in this guide gives a 4-20 mA signal with HART, and all except the Dräger Pulsar 7000 publish Modbus; the Pulsar 7000 product information lists 4-20 mA (source and sink) and HART 7. Map the low-current levels each model uses for beam block, warning and fault in your PLC or fire and gas panel, so operators can tell a blocked beam from a loop fault.

• Relays: LS2000 relays (two alarm, one fault) are optional and available on Ex d approved models only, and the Excel Plus lists a fault relay plus alarm 1 and alarm 2 relays.
• Published beam-block currents: Pulsar 7000 beam block warning at 2 mA, and Senscient ELDS beam block at 2.5 mA (configurable 0 to 3.5 mA).
• Termination: the LS2000 may be used with the FM Approved PointWatch Termination Box Model PIRTB.

How is an open-path gas detector aligned, mounted and maintained?

An open-path gas detector is aligned at commissioning, and its published misalignment tolerance sets how rigid the mounting must be: ±0.8° for the LS2000 and Searchline Excel Plus, ±0.5° for the Senscient ELDS, and ±0.6° for the Pulsar 7000 (±1.6° with the Tx S transmitter). Mount both units at the same elevation, high enough to keep people and vehicles out of the beam, and away from turbine exhausts, flare stacks and process vents. On the LS2000, span calibration in the field is not required: field work is zero calibration with the on-board magnetic reed switch and functional checks with test films or a gas test cell.

• What ±0.8° means on the ground: about ±56 cm at 40 m and ±168 cm at 120 m, and Honeywell limits supporting-structure movement to ±0.5°, tighter than the detector tolerance.
• Mounting details: Det-Tronics describes a suitable mount as a 4 m long, 100 mm diameter post in a 1 m deep concrete foundation, notes that for methane about 2 m above grade minimizes beam blocks from human activity, and warns against a receiver that sees more than one transmitter, a common concern on pipelines.
• Alignment tools: LS2000 telescope (Alignment Tool 012287-002), Honeywell Alignment Scope 2017B0299, MSA scope A-5000-1 and Teledyne kit OPGD-888247-1, while Dräger aligns the Pulsar 7000 with a handheld terminal instead of a telescope.
• Self-testing laser: MSA’s ELDS runs a daily automatic end-to-end functional test and is factory calibrated for life.

When does a laser open-path gas detector make sense instead of infrared?

A laser open-path gas detector makes sense for methane leak detection when methane is the one target gas and you want a low full scale. The infrared units in this guide respond to a broad family of hydrocarbons, while MSA’s Senscient ELDS uses Enhanced Laser Diode Spectroscopy, is sold per target gas and offers a 0 to 1 LEL.m range.

What the documents add: MSA’s 0 to 1000 ppm.m methane range is only available in the 5 to 40 m and 40 to 120 m path lengths, and MSA states that a laser OPGD is target gas-specific with the highest uptime in severe weather, which is a manufacturer claim. On the infrared side, Det-Tronics’ line-of-sight application scope excludes hydrogen, and the Searchline Excel Plus defaults to a Universal Hydrocarbon calibration.

How do current open-path gas detectors compare on published data?

Values and approval strings as printed; “not published” means absent from the listed document.

Where can you buy an open-path gas detector, and what should you ask the supplier?

Buy an open-path gas detector from a distributor that can quote the full kit for your range band, target gas, approval code and SIL option, with the commissioning accessories. PE Energy Industrial Supply in Houston, TX is an authorized Det-Tronics distributor and lists the FlexSight LS2000, an LS2000 kit, the LS2000 Mounting Adapter 6″, Laser Aligner Assembly and Laser Aligner Target, and the PointWatch Eclipse PIRECL with its calibration kits. PE also lists the Teledyne SafEye and the Spectrex SafEye Quasar 900 open path detectors.

• Model status: MSA marks the Ultima OPIR-5 discontinued, Dräger marks the Polytron Pulsar 2 End of Sales with the Pulsar 7000 as its new version, and the LS2000 replaces the Open Path Eclipse (OPECL), manufactured from 2004 to September 2019.
• Relays and SIL: relays come only on Ex d approved LS2000 models, and the Safety-Certified version is identified on the label.
• Test parts: LS2000 Alignment Tool 012287-002, System Test Films 012673-001 and Gas Test Cell, LS2000 Methane ISO 009246-003.

Where do these figures come from?

• Det-Tronics: LS2000 spec sheet 90-1215 rev 4.1, LS2000 manual 95-8714 rev 7.2 (July 2025), LS2000 safety manual 95-8727 rev 1.2, migration sheet 92-1077 1.4, gas brochure 92-1066-2.4, PIRECL spec sheet 90-1138 rev 12.4, the LS2000 page and the line-of-sight detectors page.
• Honeywell: Searchline Excel Plus data sheet Rev A 1/21, Plus/Edge technical manual Issue 4 (June 2024) and TÜV SÜD SIL certificate Z10 096351 0004 Rev. 00.
• Dräger: Pulsar 7000 product information 91 02 343, instructions for use 90 33 451 (October 2019), Notes on Approvals 90 33 710 (August 2024), and the Pulsar 7000 and Polytron Pulsar 2 pages.
• MSA: Senscient ELDS methane data sheets 1411-018-MC (08.2022, FM 6325 approved) and 1411-09-MC (02.2024) and 1411-11-MC (commissioning), via the Senscient ELDS page, and the Ultima OPIR-5 page.
• Teledyne: open path brochure GF30166E-EN (2022) and the SafEye page.

Summary: how to choose an open-path gas detector

• Match the band to the distance: it must bracket each beam, and its short end may need an aperture kit.
• Treat a beam block as lost coverage: know the delays and map the mA levels in your panel.
• Copy approvals from the label: marking and performance approval are separate, and editions can disagree.
• Read the SIL scope, not the headline: versions, outputs and certificate dates differ (Honeywell: valid until November 18, 2026).
• Plan alignment and testing at purchase: tolerances run from ±0.5° to ±0.8°, and tools and test parts belong on the same order.
• Check the model is still sold: the MSA Ultima OPIR-5 is discontinued and the Dräger Polytron Pulsar 2 is End of Sales.