Open Path Combustible Gas Detector Quasar 900

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).

open path gas detectors

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.

Long Distance Detection Range

Detect up to 660 feet (200 m)

DOAS Technique

Analyze the “spectral fingerprint” of the atmosphere to provide a stable gas reading with a response time of 3 seconds

Built-In Event Recorder

Record and review the last 100 events

Durable, Compact Design

Withstand and operate in harsh environmental conditions with virtually no fluctuations in gas readings

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

+/- 0.5°

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


  • 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

Tilt Mount: 4.2 lb. (1.9 Kg)


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

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