HYDROGEN DETECTION AND THE HYDROGEN ECONOMY

COMMON HYDROGEN DETECTION TECHNOLOGIES

ELECTROCHEMICAL CELLS 

- Detection range: up to 40.000ppm (4%vol)
- Typical long-term drift: 2%/month
- Typical operating life:  24 months in air
- Cross sensitivity to other gases
- Potential replacement required after high exposures 
- Can only operate in presence of Oxygen

CATALYTIC BEAD SENSORS

- Detection range: up to 100% LFL (4%vol)
- Effectively Linear to 60% LEL
- Typical long-term drift: 5% LEL/3 Months 
- Reacts to any flammable gas
- Potential replacement required after high exposures 
- Susceptible to contamination and poisoning 
- Can only operate in presence of Oxygen

With these limitations in mind, NET has developed the MAK (MEMS Analogue Katharometer) series of sensors, a new intelligent sensor based on thermal conductivity technology set to hit the market in Q4/2024. 

A thermal conductivity gas sensor, also known as a katharometer, measure the concentration of gases having thermal conductivity significantly different to a reference gas (normally, air), between 0 and 100% volume. Thermal conductivity sensors are most effective when detecting gases with low molecular weight, which correspond to greater thermal conductivity – such as Hydrogen, possesses the highest thermal conductivity of all known gases. 

THERMAL CONDUCTIVITY OR KATHAROMETER GAS TECHNOLOGY

Thermal conductivity is a well-known technology in gas detection, although historically its use has been limited due to a number of technological challenges. 

A thermal conductivity gas sensor, also known as a katharometer, is a common technology allowing measurement of the concentration of flammable gases. Its main advantage over traditional catalytic sensors (or pellistors) is their ability to measure levels of concentration above the Lower Flammability Level (LFL). However, traditional thermal conductivity gas sensors suffer from high power requirements and demand high level of precision and craftsmanship in manufacturing, and this has so far prevented a widespread use in industrial safety applications. 

With the application of MEMS (Micro Electronic Mechanical Systems) technology, NET is now crushing those barriers. MEMS are systems combining microscopic components, incorporating both electronic and moving parts, and are fabricated using semiconductor manufacturing techniques.

By employing very repeatable, high-volume CMOS (Complementary metal-oxide-semiconductor) MEMS technology, the new NET KATHAROMETER GAS TECHNOLOGY is significantly lowering production costs and power consumption of thermal conductivity gas sensors. 

Thermal conductivity is a property that describes a material’s ability to transfer or conduct heat. Thermal conductivity sensors measure the concentration of gases having thermal conductivity significantly different to a reference gas (normally, air), between 0 and 100% volume. Gases with thermal conductivity similar to air, notably oxygen, nitrogen and CO, in fact, cannot be measured using this technique.  

A thermal conductivity gas sensor is formed by two dies – one freely exposed to the target gas (the active die) and the other sealed in a chamber containing air (the reference die). Both dies are heated using constant current and run in a classic Wheatstone bridge circuit. Thermal conductivity sensors measure the change in heat loss of the active die in the presence of the target gas. In fact, when the active die is exposed to a gas with thermal conductivity different to that of air, the rate of heat loss from the die will change and so will its resistance. This change is compared with the resistance of the reference die. 

For the reasons detailed above, thermal conductivity sensors are subject to specific cross sensitivity with other gases whose thermal conductivity is also significantly different from that of air. Therefore, thermal conductivity sensors perform best in applications where interfering gases are absent, or their cross sensitivity is within the acceptable margin of error required by the application.

Thermal conductivity sensors are most effective when detecting gases with low or high molecular weight ( thermal conductivity decreases with increasing molecular weight) – such as Hydrogen, a very light molecule possessing the highest thermal conductivity of all known gases, and Helium. Thermal conductivity sensors measure the concentration of gases having thermal conductivity significantly different to a reference gas (normally, air).   

THERMAL CONDUCTIVITY SENSORS

MAK Thermal conductivity sensors, unlike catalytic bead sensors and electrochemical cells, covers the broadest range of detection, working well from ppm level, up until 100 % volume. This is because they can operate without the presence of Oxygen.

MAK Thermal conductivity sensors provide far better long-term stability than sensors that are triggered by chemical reactions that eventually cause the sensor to degrade, such as electrochemical and catalytic. Thermal conductivity gas sensors, in fact, do not involve physical or chemical changes in the sensor – nor they implement light sources, moving or resonating parts which can deteriorate over time. This, coupled with outstanding resistance to poisoning and harsh environmental conditions, results in far greater operating lives than for traditional technologies.

NET MEMS membrane-based sensor offers a far greater resistance to mechanical shocks when compared to traditional catalytic or thermal conductivity sensors.  

For safe operation and to minimize power consumption, the sensor is excited with a pulsed waveform (400 ms on and 1,000 ms off), resulting in a heater temperature that is almost the same as the ambient.

Another key factor is the fast response time of the sensor, the only limiting factor being the time required for changes in the measurement resistor. 

It must be noted that a gas thermal conductivity changes with temperature and pressure. Therefore, thermal conductivity sensors are strongly affected by changes in environmental conditions. For this reason, MAK sensors are equipped with built-in temperature, relative humidity and pressure sensors and provide an active compensation of the measurement and the corresponding output against environmental variations.  

MAK sensors have identical form factor, output options and pinout configuration as standard industrial 4-series NIDR sensors, including voltage and bridge output. This will grant a flawless transition to all gas detection system manufacturers already familiar with this type of technology. 

The world may not be ready yet for the transition to the Hydrogen Economy, but NET is – with the new MAK series of sensors. 

MAK SENSORS HIGHLIGHTS

- Individual calibration and testing, for measurements you can trust
- Extended temperature range (-40 °C to +60 °C), for use in any environment
- Active Environmental compensation (Temperature, RH, Pressure)
- Internal microprocessor, for advanced signal processing
- Standard industrial size, to fit existing detectors
- Low power consumption 
- Fast T90 response time, for critical and life-saving applications
- Outstanding long-term stability of 0.1 % F.S./year
- Broadest available ranges
- ModBus digital communication, for ease of integration
- Signal versatility: voltage and optional bridge or pellistor output
- Solid, rugged construction with stainless steel enclosure
- Standard industrial accepted negative or positive pinout