Net Safety™ Millennium II ST3 XChem Toxic Gas Sensors

The Net Safety Millennium II ST3 XChem Toxic Gas Sensor provides high-specificity toxic gas detection using electrochemical sensing technology designed for demanding industrial environments. As part of the Net Safety Millennium II gas detection platform, the ST3 XChem series is compatible with the Net Safety Millennium II M21, M22, and M2B transmitters, allowing facilities to build flexible fixed gas detection systems based on site-specific monitoring requirements.

ST3 XChem sensors are designed to support fast response, long sensor life, low power consumption, and reliable performance in environments where toxic gas monitoring is critical for worker safety and process protection. The SimpleClick sensor design allows the transmitter to automatically recognize the sensor configuration, helping reduce installation time and simplify sensor replacement.

Available configurations include sensors for hydrogen sulfide, carbon monoxide, and oxygen deficiency detection. Additional ST3 XChem toxic gas sensor configurations may be available; please contact Westech Industrial for current options.

Westech Industrial offers Net Safety toxic gas detection products in BC, AB, and SK, along with technical consultation, service support, and custom fabrication capabilities. Our team can help with sensor selection, gas detection system design, custom enclosures, panels, and integrated solutions for industrial safety applications.

Net Safety™ Millennium II ST3 XChem Toxic Gas Sensors
Net Safety™ Millennium II ST3 XChem Toxic Gas Sensors - Image 2

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Description

Electrochemical Toxic Gas Detection

The ST3 XChem series uses electrochemical sensing technology to detect target gases with strong specificity. As a result, it supports reliable toxic gas monitoring in demanding industrial environments. Each XChem toxic gas sensor is designed for fixed gas detection applications where accurate readings matter. Therefore, facilities can use it to help protect personnel, equipment, and process areas.

Millennium II Transmitter Compatibility

ST3 XChem sensors work with the Net Safety Millennium II gas detection platform. They are compatible with M21, M22, and M2B transmitters, depending on the selected configuration. This compatibility gives facilities more flexibility when designing new systems or updating existing detection points. Additionally, users can configure single- or dual-channel systems to suit different monitoring needs.

SimpleClick Plug-and-Play Sensor Design

The SimpleClick design helps simplify installation and replacement. Emerson calibrates the sensors at the factory before shipment. Then, the Millennium II transmitter automatically recognizes the installed sensor. It also uploads the correct configuration profile. As a result, teams can reduce setup time and minimize configuration errors during maintenance.

Sensor End-of-Life Diagnostics

Electrochemical sensors require replacement as part of their normal lifecycle. Therefore, the ST3 XChem series includes sensor end-of-life diagnostics. This feature monitors the health of the sensor cell. Then, it provides a fault alert when the sensor needs replacement. This helps maintenance teams plan service before detection reliability becomes a concern.

Single or Dual Channel Flexibility

A single Millennium II transmitter can support one or two sensors. Users can connect toxic gas sensors, combustible gas sensors, or both. This flexibility helps facilities reduce the need for multiple gas-specific detectors. It also allows teams to match sensor types to site hazards more efficiently.

Improved Triple Electrode Design

Each sensing element uses sensing, reference, and counter electrodes. These electrodes use robust materials to support long life and dependable performance. In addition, the design helps the XChem toxic gas sensor maintain stable operation in challenging conditions.

Field-Selectable Gas Ranges

Applicable sensor configurations support field-selectable gas ranges. This allows users to adjust the detection range based on application needs. As a result, facilities can better align sensor performance with site-specific toxic gas hazards.

Long-Range Sensor Separation

ST3 XChem sensors can be installed up to 2,000 ft. from the transmitter. This setup uses 18 AWG cabling and digital communication. Therefore, teams can place the sensor near the hazard while keeping the transmitter accessible. This is useful in large facilities and hard-to-reach monitoring areas.

Advanced Environmental Immunity

Each sensor is temperature compensated for its target gas and selected gas range. Also, an advanced diffusion process helps control humidity effects. A hydrophobic barrier supports stable gas readings in harsh environments. Together, these features help improve confidence in gas concentration measurements.

Low Power Consumption

The ST3 XChem series uses low power during operation. This helps reduce system load in fixed gas detection applications. As a result, the XChem toxic gas sensor supports efficient, reliable toxic gas monitoring across industrial sites.

Applications

The Net Safety Millennium II ST3 XChem Toxic Gas Sensor is suitable for industrial environments where toxic gas detection is required to support worker safety, process safety, and regulatory compliance. Its transmitter compatibility, long-range sensor separation, and field-serviceable design make it well suited for both new installations and upgrades to existing gas detection systems.

Common applications include:

  • Refineries
  • Chemical plants
  • Water and wastewater treatment facilities
  • Mining operations
  • Pulp and paper facilities
  • Power generation plants
  • Industrial process areas requiring toxic gas monitoring
  • Remote or hard-to-access monitoring points where sensor separation from the transmitter is beneficial

Documents

Emerson_Net Safety_ST3 XChem_Data sheet_May2026_Westech.pdf

Emerson Net Safety-FGD-BRO-Safety-Monitoring_Westech_Sept_10_2020.pdf

 

Manufacturer info

Emerson concentrates on the most complex and profound challenges facing the world in the process, industrial, commercial and residential markets. We refocused our business portfolio to deliver solutions that bring greater value to our customers. Learn how we’ve transformed and why.

https://www.emerson.com

SPECS

Product Series:
Net Safety ST3 XChem Toxic Gas Sensor, Millennium II Series Sensors.
Sensor Technology:
Electrochemical.
Platform Compatibility:
Net Safety Millennium II Gas Detection platform.
Compatible Transmitters for H₂S and CO Configurations:
Net Safety Millennium II M2B, M21, and M22.
Compatible Transmitters for O₂ Deficiency Configuration:
Net Safety Millennium II M21-AH-A/S and M21-AHR-A/S.
Common Gas Configurations:
Hydrogen sulfide (H₂S), carbon monoxide (CO), and oxygen deficiency (O₂).
Sensor Separation:
Up to 2,000 ft. (600 m) with 18 AWG cabling.
Enclosure Materials:
AL6061 aluminum or SS316 stainless steel.
Ingress Protection:
IP64.
Warranty:
Two years.
Electromagnetic Compatibility (EMC):
EN 50270:2006.
North American Markings:
Class I, Division 1, Groups BCD T5; Ex d IIB+H₂ T5; Class I, Zone 1, AEx d IIB+H₂ T5 Gb; Type 4X, IP64.
IECEx Marking:
Ex db IIB+H₂ T5 Gb.
IECEx Ambient Marking:
-40°F to +167°F (-40°C to +75°C).
IECEx Special Condition of Use:
Flameproof joints are not intended to be repaired.
H₂S Part Number:
ST320(A/S)-100-ASSY.
H₂S Detection Range:
0–20/50/100 ppm, field-selectable.
H₂S Response Time:
T20: 10 seconds; T50: 15 seconds; T90: 36 seconds.
H₂S Accuracy:
±3 ppm or 10 percent of reading, whichever is greater.
H₂S Zero Drift:
Less than 5 percent full scale annually.
H₂S Repeatability:
Less than 1 percent full scale.
H₂S Calibration Frequency:
Six months.
H₂S Operating Temperature Limits:
-40°F to +140°F (-40°C to +60°C).
H₂S Storage Temperature Limits:
-40°F to +140°F (-40°C to +60°C).
H₂S Humidity Limits:
15–90 percent relative humidity, non-condensing.
CO Part Number:
ST360(A/S)-1000-ASSY.
CO Detection Range:
0–500/1000 ppm, field-selectable.
CO Response Time Without Accessories:
T20: 10 seconds; T50: 15 seconds; T90: 30 seconds.
CO Accuracy:
32°F to 122°F (0°C to 50°C): ±13 ppm or 5 percent of reading, whichever is greater; -4°F to 32°F (-20°C to 0°C): ±32 ppm or 17 percent of reading, whichever is greater.
CO Zero Drift:
Less than 5 percent full scale annually.
CO Repeatability:
Less than 3 percent full scale.
CO Calibration Frequency:
Three months.
CO Operating Temperature Limits:
-4°F to +122°F (-20°C to +50°C).
CO Storage Temperature Limits:
37°F to 68°F (3°C to 30°C).
CO Humidity Limits:
15–90 percent relative humidity, non-condensing.
CO Enclosure Weight:
Stainless steel: 3.5 lb. (1.4 kg); aluminum: 1 lb. (0.4 kg).
O₂ Deficiency Part Number:
ST341(A/S)-25-ASSY.
O₂ Detection Range:
0–25 percent volume.
O₂ Response Time Without Accessories:
T20: 7 seconds; T50: 10 seconds; T90: 20 seconds.
O₂ Accuracy:
±0.5 percent volume.
O₂ Zero Drift:
Less than 5 percent full scale annually.
O₂ Repeatability:
Less than 3 percent full scale.
O₂ Calibration Frequency:
Three months.
O₂ Operating Temperature Limits:
-4°F to +122°F (-20°C to +50°C).
O₂ Storage Temperature Limits:
32°F to 68°F (0°C to 20°C).
O₂ Humidity Limits:
15–90 percent relative humidity, non-condensing.
O₂ Enclosure Weight:
Stainless steel: 3.5 lb. (1.4 kg); aluminum: 1 lb. (0.4 kg).

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PRODUCT FAQ's

What gases can the Net Safety ST3 XChem Toxic Gas Sensor detect?
ST3 XChem sensors are available for a variety of toxic gas detection applications. Common configurations include hydrogen sulfide, carbon monoxide, and oxygen deficiency configurations. Contact Westech Industrial for the full list of available sensor options.
Which transmitters are compatible with the ST3 XChem Toxic Gas Sensor?
For hydrogen sulfide and carbon monoxide configurations, the datasheet lists compatibility with the Net Safety Millennium II M2B, M21, and M22 transmitters. The oxygen deficiency configuration is listed for use only with the Net Safety Millennium II M21-AH-A/S and M21-AHR-A/S transmitters.
What is the SimpleClick sensor design?
The SimpleClick sensor design allows the sensor to be installed with less setup time. The sensors are calibrated at the factory, and the Millennium II transmitter automatically recognizes the newly installed sensor and uploads its configuration profile.
How far can the sensor be installed from the transmitter?
The ST3 XChem sensor can be separated from the transmitter by up to 2,000 ft. (600 m) using 18 AWG cabling. This supports remote sensor placement in areas where the transmitter may need to be installed in a more accessible or practical location.
How often does the ST3 XChem sensor need calibration?
Calibration frequency depends on the sensor configuration. The datasheet lists a six-month calibration frequency for the hydrogen sulfide sensor and a three-month calibration frequency for carbon monoxide and oxygen deficiency configurations.
What does the sensor end-of-life diagnostic do?
Electrochemical sensors have a normal operating lifecycle and must be replaced over time. The ST3 XChem end-of-life diagnostic monitors the health of the sensor cell and provides a fault condition alert when the sensor requires replacement.
Can Westech Industrial help select the correct toxic gas sensor?
Yes. Westech Industrial can help review the target gas, required detection range, transmitter compatibility, installation environment, and service requirements to help select the correct ST3 XChem sensor configuration for your application.
Does Westech Industrial provide service support for Net Safety gas detection systems?
Yes. Westech Industrial offers service support for industrial gas detection applications, including assistance with system selection, troubleshooting, calibration planning, and sensor replacement support.
Can Westech Industrial provide custom fabrication for gas detection applications?
Yes. Westech Industrial can support custom fabrication requirements for gas detection systems, including custom panels, enclosures, mounting arrangements, and integrated safety solutions based on site requirements.
Is the ST3 XChem suitable for harsh industrial environments?
Yes. The ST3 XChem series is designed for extreme industrial environments. The sensors include temperature compensation, humidity control through an advanced diffusion process, and a hydrophobic barrier to help maintain stable gas concentration readings.