Heat-gas gauge: years-proven, future-proof

Temperature technology is a proven method for measuring the flow of gases and liquids. Recent advances in technology and small-scale production have allowed technology to be used as a natural gas meter for large, cost-effective applications.

Two studies published in 2021 now confirm the long-term reliability of this technology for applications in difficult environments. After more than 10 years of work in the field, the researchers examined temperature gauges. All meters operate within the specified accuracy limits during service and most meters still meet the requirements for new gas meters.

A.D. With the release of the European standard in 2021 (EN 17526), ​​thermal gas technology is a cost-effective, proven and reliable solution for the gas scale, which will power millions of gas meters worldwide. In addition, it offers a wide range of auto and network-detection capabilities and is ready for a variety of natural gas compounds, including hydrogen compounds and pure hydrogen.

The principle of temperature-measurement

For the past 80 years, heat-mass technology has been used to measure flow in such important applications

Figure 1: The principle of temperature-measurement. Heating and two temperature sensors can be combined on
Single silicon chip. Exhaust gas changes the profile of the heat exchanger around the heater. The temperature
The difference between the two temperature sensors is proportional to the amount of gas flowing.

Life-sustaining medical ventilation, regulation of ventilation in combustion engines, construction of ventilation systems and control of emotional industrial processes. Thermometer is a very versatile and robust way to measure flow.

Until recently, however, it was too expensive for high-end, cost-effective apps. With the advancement of MEMS (microelectromechanical system) technology, the principle of heat-mass flow measurement has been realized on a single silicon chip. Highly integrated CMOS processing of such chips allows for efficient small production
And large-scale production. With these developments, the cost of heat-bulk technology has decreased significantly
An attractive solution not only for high-end applications but also for low-cost, high-volume devices such as disposable flow sensors and gas meters.

Temperature-quantity technology for gas measurement

The application of heat-bulk technology in gas meters was developed by the Censor in the early 2000s. The main advantages of this application are excellent accuracy, compact size, extremely low power consumption (critical for battery powered gas meters) and most importantly, very attractive price. The latter is possible with integrated sensor integration, signal processing and analysis electronics and measurement data storage in a semiconductor chip. In addition to flow, temperature sensors can also measure different gas properties to compensate for differences in gas composition.

Figure 2: An experimental setting used by NMI to test the field-returned industrial meters produced by METARSIT.

This makes it a suitable choice for temperature gauges for mixing with hydrogen or pure hydrogen for a wide range of composition as well as for gas mixtures.

A.D. In 2007, the first heat-gas gauges were installed in the field. Following the gradual adoption of the technology, emissions have accelerated in recent years, and more than 6 million meters of gas are relied upon to measure gas flow worldwide. . The main reason for the adoption of technology is the lack of follow-up in the field. In many other applications, heat-transfer technology has been proven over the years, but it is a relatively newcomer to the gas metering industry: an industry that values ​​strong performance, safety and reliability above all else. Various national and international standards regulate the required gas accuracy. There are a variety of accuracy lessons, and Section 1.5 is widely used around the world.
OIML R137 and EN 17526 (Special Heat Gas Gas Measurement, published in 2021) Heat-Compensation Section 1.5 Gas Meters (such as Temperature Meters) 2% and 3.5% in high and low flow regimes respectively.

OIML R137 also orders 2x MPE (3.5% / 6.5%) for metered meters following online service. As a result, the 2x MPE one meter in service (typically 10-15 years) is widely accepted.

Field studies of the reliability of temperature-mass gauges

A.D. By 2021, the vast majority of thermometers have already been in the field for more than a decade.
Two independent studies have recently looked at how different types of thermometers work after more than 10 years in gas. The first study, conducted by NMI – a Dutch notification body – led by Metarsit, looked at the industrial G10, G16 and G25 meters installed in Italy between 2013 and 2016, and between 2013 and 2016, the institute selected 20 meters from the 2,749 list. These were later assembled by the manufacturer (19m-one installed in an inaccessible area) and sent to the NM to measure back. The stated measurement involves measuring the flow rate between Qmin and Qmax per meter of air and natural gas. Regardless of the number of years in service and the amount of gas stored, it was found that all meters were still within the allowed 2x MPE. In addition, all meters were done in 1x MPE with gas, and 15 out of 19 meters were also done in the air. That is, most of the meters as well as the new-equipment were done.

The second study covered 35 EGZ G4 residential meters built in ABB and installed in Switzerland from 2010 to 2011. These meters lasted 9 to 10 years before being re-measured. The study was conducted by MEMS AG and the measurement infrastructure was developed by the Swiss Federal Meteorological Institute, Metas. Again, the authors measured all the meters between air and natural gas between Qmin and Qmax flow levels. Similar to the NMI study, all measurements were performed well in 2x MPE in air and gas. In addition, all 35 meters were still gas tested at 1x MPE, and 31 of the 35 were in the air.

Three of the 35 meters measured were installed in a pressure-reducing station and experienced an unusual flow. In fact, they stored approximately 14 times higher than the other 32 meters (280,000 m3 for 20 years over 20 meters over 20 200 m3). It takes an average of 140 years to store the measured amount of gas. Importantly, all 3 meters were still within 1x MPE for both air and natural gas – for new gas meters. What the two studies have in common is that the experimental gas measurements are based on

Figure 3 – Natural gas and Q) flow errors between 35 EGZ G4 meters between Qmin and Qmax. The blue and red broken lines represent the highest
Errors allowed in OIML R137: 1x MPE for new meters (blue) and 2x MPE for field return measurements (red). The black broken line represents the average
35 Measurements.

CMOSense® gas metering modules for key meteorological units manufactured by Sensirion AG. In addition, after more than 10 years in the field, thermal-mass gauges are still as good as new.
If the errors are doubled over the next 10 years (no indication), the measurements will still be within the 2x MPE approved by OIML R137.

Thus, one can conclude that thermometers have been able to operate safely in the field for more than 20 years. This extends the lifespan of a conventional gas meter. The meteorological unit seems to be more stable, as it is not affected by the measured gas (14x average). Therefore, it can be concluded that the other meters are easily extended.

TS EN 17526-New Heat-Gas Gas Measurement Standard

The maturity of heat-bulk technology for gas metering applications has been recognized by CEN in 2021. “EN 17526. Gas gauges. Thermal-mass flowmeter based gas meter lists the requirements and tests required to bring temperature-mass gas meters into the field. It is a standardized standard, which means it is built on standard documents previously developed for diaphragm and ultrasound gas measurements. It is also compliant with international standards such as OIML R137. Measurement manufacturers used for existing standards should not find any surprises in the new temperature regulation. From now on, the heat-gas standard for him will eliminate the high level of distrust associated with verifying such meters in the past because the requirements and test plans are clearly stated in the specific criteria.

Heat-gas gauge: years-proven, future-proof

Recent developments have brought the cost of heat-bulk technology to a very high level
An attractive solution for gas meter applications. Long-term field reliability studies indicate that the lifespan of heat-bulk gas meter modules is much longer than that of conventional gas meter design. A.D. By 2021, the publication of a dedicated thermo-gas meter will recognize the technological maturity and pave the way for widespread adoption of this well-established method of measuring flow in the gas metering industry. In addition to attractive price, reliability, and compact size, heat-bulk technology also offers a wide range of self-monitoring and network-detection capabilities (e.g., air-conditioning detection). Finally, the technology can measure natural gas in a wide range of settings, as well as easily withstand natural concentrations of pure gas-hydrogen from any concentration and pure hydrogen.

About the author

Dr. Conrad Domsinski is the product manager at Censorion. It is responsible for the interpretation, production life cycle management and certification of heat-mass sensor solutions used in modern gas measuring products worldwide. Dominski holds a PhD in material science from the Swiss Federal Institute of Technology (PFL) in Lausanne, with extensive experience in international project management.

About Sensirion – Experts in Environment and Flow Sensor Solutions

Sensirion AG is a leading manufacturer of digital microscopes and systems. Its product range includes gas and liquid flow sensors, humidity and temperature sensors, volatile organic compounds, carbon dioxide and micronutrients to measure pressure sensors and environmental sensors.

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