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CO233A – Carbon Monoxide Gas Sensor with Display

The CO233A is Carbon Monoxide (CO) gas sensor with display for detection of Carbon Monoxide (CO). The sensor is compatible with the complete range of Duomo conventional gas controllers. It features a Time weighted average (TWA) feature that can indicate when gas levels have been over lower levels for a set time periods.

Other versions

Quantity discount

Quantity 1 - 4 5 - 9 10 - 19 20+
Price £291.21 £276.65 £262.09 £247.53



CO233A- Carbon Monoxide Gas Sensor Certified EN50291 for Toxic Gas 12-24V DC Supply

The CO233A is an essential Carbon Monoxide gas sensor, designed for professionals in the gas safety and control industry. It provides a 4-20mA signal output that is sent to any of the Duomo controller panels listed.

The 6 colour display informs the user of the status and CO levels. For example the Short term exposure limit (STEL) over 15 minutes and the time weighted average (TWA) over 8 hours. These levels are constantly tested and the display changes accordingly. 300ppm activates the main alarm relay. Another key point is the 0-300ppm linear output conforms to the 4-20mA standard. Making it easy to monitor and track CO levels accurately. This provides a signal if gas levels stay above a concentration over a given time period, such as 30ppm for 120 minutes. This makes the CO233A sensor invaluable for monitoring CO levels in boiler rooms as part of a complete gas detection system.

EN50270 & EN45544-1-3 Compliant

The CO233A sensor is EN50270 & EN45544-1-3 Compliant. Making the sensor a reliable solution for detecting Carbon Monoxide (CO) in various applications. It is designed with electrochemical sensor technology for accurate detection and measurement.

4-20mA Signal Output

With the CO233A sensor’s 4-20mA signal output, you can monitor and track CO levels easily. It features both linear and on/off time-weighted average signals.

Compatibility with Various Gas Controllers

The CO233A sensor is compatible with Duomo’s GS100M, GS300M, GS300Mc, BX444Mc, BX150, and BX316 conventional gas controllers. It offers a seamless integration experience.

Protective Ratings

Offering IP66 protective rating for enclosure and IP65 protective rating for the sintered head. The CO233A sensor performs well even under harsh working conditions. It is built to last and ensures safety and reliability.

CE Certified

The CO233A sensor is CE certified as per no. 96125. It meets the strict safety and performance standards set by the European Union.

Multiple Versions

The CO100AR is a CO233A sensor version without a display, allowing for easy readings and visual validation of CO levels.

The CO100P is specifically set up for use in car parks, providing a tailored solution for CO monitoring needs in such environments.

Long-Term Reliability with 3-Year Guarantee

Duomo’s CO233A sensor comes with a 3-year guarantee, ensuring its long-term reliability and performance. Rest assured that our team values honesty, comprehensive support, and the ability to adapt and evolve beyond the present.

At Duomo, we’re proud to provide solutions that improve safety and efficiency. The CO233A sensor is just one of many innovative products that we offer. We’re here not just for today, but for the next 25 years and beyond, constantly adapting and evolving to meet the needs of our customers.


Product Details

  • Autosetting feature for calibration and Diagnosis
  • Preset to TWA and STEL Standards
  • 6 Colour Display for increased visibility
  • IP65 Protection
  • 4-20mA Industry Standard Output
  • Conventional GS or BX Control Unit Compatible
  • EN50270 & EN45544-1-3 Compliant
  • 3 year guarantee


Onsite Diagnostics

If you require onsite diagnostics or technical assistance with any of our products please contact us

  • This field is for validation purposes and should be left unchanged.


We recommend Duomo Gas Detection products are serviced at least annually to ensure efficacy and extend sensor life. Our qualified team of engineers are available Nationwide.



  • CO233A Datasheet

    2.11 MB | pdf



How do I know how many sensors I need and the area each sensor covers?

Each sensor covers an area of 6 metres diameter

What height should the sensor be mounted?

The position of the sensor is a crucial factor for its correct functioning. The sensor must be placed at a height of 160 cm from the lowest point on the floor.

The sensor must not be placed near furnaces, fuel-burning kitchen appliances, fireplaces, ranges, suction fans, ventilation fans, windows, doors. Smoke vapour and sources of heat could distort its measurement.

What do the LED indicator colours mean?

When the LED is Green in colour it indicates that the toxic gas threshold has not been exceeded and the sensor is in normal condition.

When the LED is Cyan in colour it indicates the maximum average concentration to which an unprotected worker may be exposed in any eight-hour interval during the
day has been detected (20ppm) and the main alarm relay has triggered.

When the LED is Magenta in colour it indicates that the maximum average concentration to which an unprotected worker may be exposed in any fifteen-minute interval during the day has been detected (100ppm) and the main alarm relay has triggered.

When the LED is Red in colour it indicates the toxic gas threshold has been reached or passed. If the 300 ppm has detected the main alarm relay is triggered immediately.

When the LED is Yellow in colour it indicates a sensor fault. This immediately triggers the fault relay

What is the TWA & STEL alarm?

TWA Time weighted average alarm is activated if the 8 hours average is over 20ppm. LED indicator illuminates CYAN

The STEL Short Term Exposure Limit alarm is activated if the 15 minutes average is over 100ppm. LED indicator illuminates MAGENTA

Fault LED is illuminated

Check that the cables are connected according to the drawing, and that the wire isolation sheath has not been pinched.

Check the voltage at the terminals 1-2.
It must be a minimum of 11VDC and a maximum of 25VDC.

Check the voltage at the terminals 2-3.
It must be a minimum of 0.8 VDC to a maximum of 1.1 VDC.

The sensor does not power up

Check that the 12/24 VDC power is present, and that positive and negative polarity has not been inverted.


Support & Service

If you require technical assistance or an annual service on this product please contact us and we will be happy to help. Our qualified team of engineers are available Nationwide.

Duomo (UK) Ltd

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