Electrochemical 2-Wire Toxic Gas Sensor Module 4501-XX

Sierra Monitor’s 4501-XX module monitors toxic gases such as Hydrogen Sulfide (H2S), Carbon Monoxide (CO), Oxygen (O2) Deficiency, Chlorine Dioxide (ClO2), and others.

The 4501-XX module is based on electrochemical technology, a proven, less-expensive option that offers high accuracy, low power requirements, and sensitivity to a particular gas in the parts-per-million range.

Utilizing 2-wire loop-powered technology, the 4501-XX module requires less wiring when being installed, leading to better protection against wiring errors. This also allows for a direct interface to common PLC and DCS. With its compact size, the 4501-XX requires minimal maintenance with a 180 day calibration cycle and continuous self-diagnostics.

The Electrochemical 2-Wire Toxic Gas Sensor Module 4501-XX is approved and certified by a variety of third party agencies, including FM, CSA, ATEX, and IECEx. These approvals and certifications assure our customers that we carry only the highest quality of products and performance.

Electrochemical 2-Wire Toxic Gas Sensor Module 4501-XX

  • 2-Wire Loop-Powered Technology – Directly interface to common PLC and DCS and powered for easy installation and reduced installation costs
  • Non-Intrusive Calibration – Calibrate the module without declassifying the area
  • FM-Approved 6 Month Calibration Interval – Dramatically reduce maintenance for the user
  • Internal Continuous Self-Diagnostics – Automatically indicate any fault or optics problems
  • LCD Display – Easily access gas status, calibration instructions, adjustment of ranges and outputs, and diagnostic information with a user-friendly operator interface
  • 4-20 mA Output – Interface effortlessly with common factory communication links and provide flexibility for the output
  • Application Adaptability – Select various ranges and mount the sensor module in various orientations with a rotatable face plate

Specifications for Electrochemical 2-Wire Toxic Gas Sensor Module 4501-XX

Model Number Max. Gas Range (1)  Resolution Response Time (2)  Sensor Life
4501-03 O2 0-25% Vol. 0.2% Vol. <10 Seconds 20 Months
4501-04 CO 0-1,200 PPM 0.5 PPM <25 Seconds 2 Years
4501-05 H2S 0-100 PPM 0.1 PPM <30 Seconds 2 Years
4501-06 Cl2 0-10 PPM 0.1 PPM <60 Seconds 2 Years
4501-08 ClO2 0-3 PPM 0.1 PPM <60 Seconds 2 Years
4501-10 SO2 0-100 PPM 0.5 PPM <20 Seconds 2 Years
4501-12 NO2 0-20 PPM 0.2 PPM <35 Seconds 2 Years
4501-25 NH3 0-100 PPM 1.0 PPM <30 Seconds (3)
4501-26 HF 0-10 PPM 1.0 PPM <90 Seconds (3)
(1) Other ranges available (2) To 90% range (3) NH3 and HF sensor requires electrolyte recharge up to year

Sensor Type

  • Electrochemical, 2-Wire


  • Display: LCD, 2-line, 16-characters
  • Signal Output: 2-wire sensor powered analog 4-20 mA (Trouble 3.6 mA)
  • Loop Resistance: 800 ohm

Electrical Data

  • Power consumption: 0.2 watts
  • Connection type: 2-wire, loop-powered
  • Input voltage: 24 VDC nominal: 14-30 VDC
  • RFI/EMI Protection: EN50081-2, EN50082-2

Operating Range

  • Ambient Temperature Range:
    • Standard: -4o to 122oF (-20o to 50oC)
    • 4501-25/26: 14o to 113oF (-10o to 45oC)
    • Extended Temperature: Sensor and 4-20 mA will continue to operate at -40oF (-40oC) but the LCD display will decay over time if exposed to temperatures below -4o (-20oC) for significant time (not for 4501-25)
  • Storage Temperature: -4o to 122oF (-20o to 50oC)
  • Relative Humidity:
    • Standard: 15-90%
    • 4501-25/26: 20-90%


  • Dimensions (H x W x D):
    • Standard: 7.0 x 3.6 x 4.0 in. (17.8 x 9.1 x 11.2 cm)
    • 4501-25/26: 8.4 x 4.4 x 3.9 in. (21.3 x 11.2 x 9.9 cm)
  • Weight:
    • Standard: 2.2 lb. (1.0 Kg) Aluminum or 4.6 lb. (2.1 Kg) SS
    • 4501-25/26: 3.0 lb. (1.3 Kg) Aluminum or 5.0 lb. (2.3 Kg) SS
  • Enclosure: Aluminum, Stainless Steel


  • Hazardous location: Explosion proof, NEMA 4X
  • FM:
    • Class I, Div. 1, Groups B, C, D
    • Class II Div. 1, Groups E, F, G
  • CSA:
    • Class I, Div. 1, Groups B, C, D
    • Class II Div. 1, Groups E, F, G
  • 4501-05 FM Performance Approval:
    • 4501-05 Approval FM ISA-92.0.01, Part I-1998 and FM 3600
  • ATEX (4501-05): II 2G, Ex d IIB + H2 T6 TA = 22 oC to 5oC
  • IECEx (4501-05): Certificate of Approval
  • CQSTL (4501-05): Certificate for China
  • Limited warranty: 2 years

How to Purchase the Electrochemical 2-Wire Toxic Gas Sensor Module

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