NEMOTO ENVIRONMENTAL TECHNOLOGY
GAS SENSORS FOR INSTRUMENT MAKERS WORLDWIDE

At last, an Ammonia sensor that works properly, at a reasonable cost.	NT-2F Series, the perfect solution for low cost disposable toxic Gas Detectors	NT-Series, Industry standard design and performance for Industrial Gas Detectors, at a cost which will give you a competitive edge.

Electrochemical Toxic Gas Sensors
Part No.	Sensor Type	Gas & Range	Nom. Output Signal	Brief Description
NT-CO	3-Electrode	0-1000ppm CO	75nA/ppm	Standard 20mm size Electrochemical Carbon Monoxide sensor for use in Commercial and Industrial Gas Detectors and Systems.
NT-CO-LI	3-Electrode	0-1000ppm CO	50nA/ppm	Standard 20mm size Electrochemical Carbon Monoxide sensor for use in Commercial and Industrial Gas Detectors and Systems.
NT-H2S	3-Electrode	0-100ppm H2S	500nA/ppm	Standard 20mm size Electrochemical Hydrogen Sulphide sensor for use in Commercial and Industrial Gas Detectors and Systems. Standard range for General purpose occupational monitoring. Low cost design.
NT-H2S-1	3-Electrode	0-100ppm H2S	700nA/ppm	Standard 20mm size Electrochemical Hydrogen Sulphide sensor for use in Commercial and Industrial Gas Detectors and Systems. Standard range for General purpose occupational monitoring. Compatible with other similar devices
NT-NH3	3-Electrode	0-100ppm NH3	40nA/ppm	Standard 20mm size Electrochemical ammonia sensor for use in Commercial and Industrial Gas Detectors and Systems.
NT-NO2	3-Electrode	0-20ppm NO2	600nA/ppm	Standard 20mm size Electrochemical Nitrogen Dioxide sensor for use in Commercial and Industrial Gas Detectors and Systems.
NT-CO-2F	3-Electrode	0-500ppm CO	40nA/ppm	Low cost 3-Electrode Carbon Monoxide sensor for use in Disposable Portable Instruments. 2-Years working life.
NT-H2S-2F	3-Electrode	0-100ppm H2S	120nA/ppm	Low cost 3-Electrode Hydrogen Sulphide sensor for use in Disposable Portable Instruments. 24 months working life.
NT-CO-6D	3-Electrode	0-200ppm CO	50nA/ppm	Similar package as NT-CO-2F, but slightly lower cost, for disposable instruments with 6 month lifetime
NT-H2S-6D	3-Electrode	0-50ppm H2S	500nA/ppm	Similar package as NT-HS-2F, but slightly lower cost, for disposable instruments with 6 month lifetime

How Do Electrochemical Gas Sensors Work?

Electrochemical Gas Sensors are used to detect and monitor low levels of toxic gases and oxygen levels in both Domestic and Industrial situations where it is essential to ensure that the air is safe to breathe. The most common type of Electrochemical sensor is the 3-Electrode fuel Cell.

Typical Electrochemical Sensor Layout

The air being measured diffuses into the cell through the diffusion barrier (capillary)and filters. when it comes into contact with the sensing electrode, the toxic gas present in the sample undergoes an electrochemical reaction. In the case of Carbon Monoxide, for example, the reaction is:

CO + H₂O => CO₂ + 2H⁺ + 2e^-

The Carbon Dioxide generated diffuses away into the air, whilst the positively charged hydrogen ions (H+) migrate into the electrolyte. The electrons generated charge the electrode but are removed as a small electric current by the external measuring circuit.

This oxidation reaction is balanced by a corresponding reduction reaction at the Counter Electrode:

O₂ + 4H⁺ + 4e^- => 2H₂O

So at one electrode, water is consumed whilst electrons are generated, and at the other, water is recreated and electrons are consumed. Neither reaction can occur if no carbon monoxide is present. By connecting the two electrodes, the small electric current generated between them is measured as directly proportional to the concentration of CO in  the air.

The Reference Electrode controls the whole process. It remains totally immersed in electrolyte, sees no gas and is not allowed to pass any current. The Reference Electrode always remains at the same electrochemical potential (known as it's "Rest-Air Potential", dependent on the material the electrode is made from, and the electrolyte used). The sensing electrode is electrically tied to the reference electrode ensuring it's potential will not change even when it is exposed to its determinand gas and generating current. Usually the potential of the sensing electrode is maintained at exactly the same value as the reference electrode, but for some gases and some applications, performance benefits are gained by maintaining the potential of the sensing electrode at a fixed level above or below the potential of the reference. This is known as "biased" operation.