Open Path Combustible Gas Detector Quasar 900

Sierra Monitor’s Quasar 900, as manufactured by Spectrex,  is an open path gas detection system which provides continuous monitoring for combustible hydrocarbon gases such as Methane and Propane.

The Quasar 900 consists of a Xenon Flash infrared transmitter and infrared receiver, separated over a line of sight from 23 ft. (7 m) up to 650 ft. (200 m).

Using the Differential Optical Absorption Spectroscopy (DOAS) technique, the Quasar 900 employs “spectral fingerprint” analysis of the atmosphere. These analyses and real-time events can be recorded via the Built-In Event Recorder, which allows the detector to record the last 100 events. This hand-held communication unit can be connected in-situ via the intrinsically safe approved data port for prognostic and diagnostic maintenance. Other features include a heated window to eliminate condensation and icing, HART capability for digital communications, and a compact design.

The Open Path Combustible Gas Detector Quasar 900 is approved and certified by a variety of third party agencies, including FM, ATEX, IECEx, and TUV. These approvals and certifications assure our customers that we carry only the highest quality of products and performance.

Open Path Combustible Gas Detector Quasar 900

  • Long Distance Detection Range – Detect up to 660 feet (200 m)
  • Built-In Event Recorder – Record and review the last 100 events
  • DOAS Technique – Analyze the “spectral fingerprint” of the atmosphere to provide a stable gas reading with a response time of 3 seconds
  • Durable, Compact Design – Withstand and operate in harsh environmental conditions with virtually no fluctuations in gas readings

Specifications for Open Path Combustible Gas Detector Quasar 900

Detection Range

  • 901: 23-66 ft. (7-20 m)
  • 902: 50-132 ft. (15-40 m)
  • 903: 115-330 ft. (35-100 m)
  • 904: 265-660 ft. (80-200 m)

Response Time

  • 3 seconds

Immunity to False Alarm

  • Not influenced by solar radiation, hydrocarbon flames, and other external IR radiation sources

Spectral Response

  • 2.0-3.0 µm

Sensitivity Range

  • 0-5 LEL.m

Displacement/Misalignment Tolerance

  • +/- 0.5o


  • +/- 7.5% of the reading or +/- 4% of the full scale (whichever is greater)

Minimum Detectable Level

  • 0.15 LEL.m

Temperature Range

  • -67o to 149oF (-55o to 65oC)


  • Up to 95% non-condensing (withstands up to 100% RH for short periods)

Heated Optics

  • To eliminate condensation and icing on the window


  • Safety System: 3 years
  • Flash Source Bulb: 10 years

Power Supply

  • 24 VDC nominal (18-32 VDC)

Power Consumption (peak includes heated optics)

  • Detector: 250 mA (300 mA Peak)
  • Source: 250 mA (300 mA Peak)

Warm Up Time

  • 30 seconds for transmitter and receiver

Electrical Connection (specify)

  • 2 x ¾” – 14 NPT conduits or 2 x M25 x 1.5 mm ISO

Electrical Input Protection

  • According to EN50270

Electromagnetic Compatibility

  • EMI/RFI protected per NE50270

0-20 mA Current Output

  • Sink (source option configuration)
    • Maximum Load: 600 at 18-32 VDC
    • Gas Reading: 4-20 mA
    • Normal, Zero Reading: 4 mA
    • Maintenance Call: 3 mA
    • Obscuration/Misalignment/Beam Block: 2 mA
    • Zero Calibration Mode: 1 mA
    • Fault: 0 mA

RS-485 Interface – Modbus Compatible

  • The RS-485 input/output provides complete data information to a PC and receives control commands from the PC or handheld unit


  • HART communications on 0-20mA analog current (FSK) – used for maintenance and asset management

Visual Status Indicator

  • 3 color LED: Green – Power On, Yellow – Fault, Red – Alarm

Hazardous Area Approval

    • Ex d e [ia] ia IIB + H2 T4 Gb
    • Ex tb IIIC T135oC Dc IP66
    • The detector or source units have a combination of approvals. Each is a single enclosure (EExd) with integral, segregated rear terminal section (EExe) and intrinsically safe (EExia) data-port for external in-situ connection to Hand-Held Diagnostic unit
  • FM/FMC
    • Approved per Class I Div 1 Groups B, C, D, Class II, III Div 1 Groups E, F, G


  • Approved per FM6325 and tested by FM per EN60079-29-4


  • Pending per IEC61503 (TUV) per SIL-2 requirements


  • The source and detector housings are stainless steel 316L with electro polish finish. The circuit boards are conformal coated and protected from mechanical vibrations. The tilt mount is also stainless steel 316L


  • Detector/Source:  10.5 x 5.1 x 5.1 in. (267 x 130 x 130 mm)
  • Tilt Mount: 4.7 x 4.7 x 5.5 in. (120 x 120 x 158 mm)


  • Detector/Source: 11 lb. (5 Kg)
  • Tilt Mount: 4.2 lb. (1.9 Kg)

Water and Dust Tight

  • IP66 and IP68
  • NEMA 250 6P


  • Meets MIL-STD-810C for Humidity, Salt and Fog, Vibration, Mechanical Shock, High and Low Temperature

How to Purchase Open Path Combustible Gas Detector

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