Sensors for Contaminants Detection in Hydrogen Fuel: Comparison
View Latest Version
Please note this is a comparison between Version 4 by Vicky Zhou and Version 3 by Vicky Zhou.

EuSensorope’s low-carbon energy policy favors a greater use of fuel cells can be used to prevent hydrogen from reaching flammable levels by triggering alarms and technologies based onactivating ventilation or shutdown of systems. Therefore, hydrogen used as a fuel. Hydrogen delivered at the sensors are an important enabling technology for the safe use of hydrogen refueling station must be compliant with requirements stated in different standards. Currently, the quality control process is performed by offline analysis o. Sensors could even have other applications, such as contributing to ensure the lifetime of fuel cell electrical vehicles by warning if the hydrogen fuel. It is, however, beneficial to continuously monitor at least some of the contaminants onsite using chemical sensors. For hydrogen quality control with regard to contaminants, high sensitivity, integration parameters, and low cost are the most important requirementsquality is not adequate. Here, chemical sensors that respond to a particular analyte in a selective and reversible way can be used in order to indicate the presence of impurities that may be harmful to the Fuel Cell Electrical Vehicle (FCEV). 

  • sensors
  • hydrogen quality
  • FCEV
  • testing protocols

1. Introduction

Hydrogen can be used as a feedstock, a fuel, or an energy carrier and storage, and has many applications across transport, industry, power, and buildings sectors [1]. Importantly, hydrogen does not emit carbon dioxide when used. Therefore, hydrogen can help to achieve a clean and affordable energy future. The number of countries with policies that directly support investment in hydrogen technologies is increasing, along with the number of sectors they target [2]. There are around 50 targets, mandates, and policy incentives in place today that support hydrogen directly, with the majority focused on transport [3].
Europe’s low-carbon energy policy means, for example, greater use of fuel cells and technologies based around the use of hydrogen as a fuel. However, their competitiveness depends directly on their safety and the safety of the facilities where they are used. Sensing technology can ensure the safe and efficient implementation of the emerging global hydrogen market [4]. Sensors can be used to prevent hydrogen from reaching flammable levels by triggering alarms and activating ventilation or shutdown of systems [5]. Therefore, hydrogen sensors are an important enabling technology for the safe use of hydrogen. Sensors could even have other applications, such as contributing to ensure the lifetime of fuel cell electrical vehicles by warning if the hydrogen quality is not adequate. Here, chemical sensors that respond to a particular analyte in a selective and reversible way can be used in order to indicate the presence of impurities that may be harmful to the Fuel Cell Electrical Vehicle (FCEV). Commonly, the quality of the hydrogen dispensed at a Hydrogen Refueling Station (HRS) is controlled according to different standards such as ISO14687:2019 [65], EN17124:2020 [76], or SAE J2719:2011 [87] which include the following gaseous impurities to be monitored: water; total hydrocarbons; excluding methane; methane; oxygen; helium; nitrogen; argon; carbon dioxide; carbon monoxide; ammonia; formaldehyde; formic acid; total sulfur compounds; and halogenated compounds.
Guidance on the frequency of hydrogen fuel quality control is defined in the international standard ISO19880-8:2019 [98]. Currently, the quality control process is performed by offline analysis of hydrogen fuel. It consists of first collecting a sample at the nozzle of the HRS, the sample is then transported to a laboratory where analyses are performed. The complete process can take from a few days to several weeks, however, if this process has the advantage of allowing controlling the full compliance with the requirements in the international standards (ISO14687:2019 and ISO19880-8:2019). It is, therefore, beneficial to continuously monitor at least some of the contaminants onsite. In that sense, the implementation of sensors at the HRS is a promising solution, provided they function properly. Moreover, the cost of the sensors is also an important parameter. To be widely implemented at HRSs, it is here estimated that the cost for a sensor should not exceed 5000 euros but for the purpose of the entry, herein even considered sensors costing up to 10,000 euros.
Chemical sensors have gained increasing attraction for applications in environmental monitoring, industrial process monitoring, gas composition analysis, medicine, national defense, and public security [109]. Chemical gas sensors are already widely developed and used to monitor air quality with regards to ozone, nitric oxides [1110], and carbon monoxide [1211]. The Environmental Protection Agency (EPA) has been engaged in a variety of activities to help advance the understanding of air sensors [1312]. In each application, a sensor’s ability to perform the measurements must meet the end-user needs which must be identified and documented. The main metrological criteria for sensors include accuracy, baseline, cross-sensitivity or selectivity, drift, environmental effects, final indication, hysteresis, limit of quantification, linear range/measuring range, noise, operation range (temperature, pressure, and relative humidity), uncertainty, response/recovery time, reversibility, resolution, saturation, and sensitivity [1413].
According to EPA, there are currently no standard testing protocols or targets to evaluate the performance of air sensors uniformly [1514], so it is safe to assume that this is also the case for chemical sensors for hydrogen quality control. The lack of consistent testing protocols to evaluate the performance of air sensors makes it difficult to understand how air sensor data compares to that of regulatory instruments. Without these standard procedures, it is difficult to understand the performance of any given device and select sensors that are appropriately suited for a desired application.

2. Chemical Sensors for Detecting Contaminants in Hydrogen

Chemical sensors respond to a particular analyte in a selective and reversible way. Sensors are defined primarily by the mechanism by which the targeted impurity interacts with the sensing element to produce an electrical signal. Another way to categorize the chemical sensors is based on the object to be detected (gas, humidity, biological samples, etc.). There are many different types of gas sensors (semiconductor gas sensor, electrochemical gas sensor, optical gas sensor, polymer gas sensor, contact combustion gas sensor, etc.) and humidity sensors (resistance sensor, capacitive sensor, etc.). As hydrogen is a relatively new sector for sensors, manufacturers mainly propose existing solutions for other matrices (i.e., nitrogen or air). It is, therefore, important to perform an in-depth exploration with the manufacturer into the suitability of the sensor for a hydrogen matrix. For example, H2S-B4 and CO-B4 sensors from Alphasense have been tested during the MetroHyVe project [1615]. The results showed the sensors were directly overloaded in hydrogen matrix. The supplier indicated in the specifications a cross sensitivity for CO-B4 with hydrogen lower than 50 at 100 µmol/mol; this value is relatively high if compared, for example, to the indicated cross sensitivity for ethylene at 100 µmol/mol, which is below 1 [1716]. Therefore, in-depth discussions with the manufacturer may have identified the likelihood of the saturation when used for hydrogen and the low potential of these sensors for hydrogen matrices. If a commercial sensor designed for another matrix gas is to be used for hydrogen application, it is important to ensure that the hydrogen itself will not give rise to a signal before further testing. Moreover, as hydrogen’s flammability range is very wide, with a lower explosive limit (LEL) of about 4% and an upper explosive limit (UEL) of about 75%, it is preferable that the sensors are intrinsically safe. In the sections below, herein described sensors that can be used in a hydrogen matrix and can detect a given impurity at relevant detection limits (below the thresholds in ISO14687:2019 [65] and EN17124:2020 [76]).

2.1. Electrochemical Sensors

Electrochemical sensors are based on electrochemical reactions within the sensor between the gas present and the electrolyte, which produces a current. The different compositions of the electrolyte determine the selectivity and the sensitivity to target gases [1817]. Among the gaseous impurities to be monitored in hydrogen, these sensors can mostly be used for oxygen. An example of sensors that are expected to work in hydrogen matrix is the electrochemical fuel cell TO2-133 µMOL/MOL oxygen sensor from Southland Sensing [1918]. According to the manufacturer, this sensor can detect as low as 0.001 µmol/mol oxygen with a response time (T90) of 7 s. Another sensor for oxygen is the EC91 from Systech Illinois [2019]. At the cathode, oxygen is reduced to hydroxyl ions which oxidizes the metal anode where the following reaction takes place: 2Pb + O2 + 2H2O →
2 Pb(OH)2. According to the manufacturer, the detection limit is 1 µmol/mol and response time (T90) is 20 s. The OxyTrans II and Oxymaster II from DKS GmbH are other alternatives [2120].

2.2. Phosphorus Pentoxide Moisture Sensor

The principle of the measurement with a phosphorus pentoxide sensor is called coulometric hygrometry. Phosphorus pentoxide cells are used in the electrolysis of water vapor. This method is often considered to be a primary measurement method [2221]. Electrodes are coated with a thin film of phosphorus pentoxide (P2O5). As the gas stream flows through the cell, moisture is attracted to the coating and migrates through the film to the electrodes. An electrolysis reaction (water to hydrogen and oxygen) occurs and generates, according to Faraday´s law a current proportional to the concentration of the moisture [2322]. Electrodes are commonly made of platinum, however, in specific conditions, platinum can act as a catalyst in a recombination reaction between the chemisorbed hydrogen and the oxygen from the electrolysis, which may lead to erroneous measurements (overestimation) in oxygen and hydrogen matrices. The use of rhodium for the electrodes eliminates this recombination reaction. One example of sensors able to function in hydrogen matrix is the Aquatrace series from DKS GmbH which can detect from 0.05 µmol/mol water according to the manufacturer [2423]. Other examples are the Uber M-I sensor from Meeco, which is able to detect from 0.5 µmol/mol-vol of water and function in inert gases, oxygen, hydrogen and gas mixtures [2524], and the HUMITRACE II from dr. Wernecke Feuchtemesstecknik GmbH [2625].

2.3. Aluminium Oxide Moisture Sensor

The operating principle of the aluminum oxide sensor is that its capacitance varies with the moisture concentration [2726]. An aluminum layer on a ceramic support is anodized to form a thin, porous layer of aluminum oxide. The gold and the aluminum layers form the sensor electrodes. The gold layer is permeable to moisture and conductive. Water vapor in the gas stream is transported rapidly through the gold layer and equilibrates in the aluminum oxide pore walls, affecting the dielectric constant of the material and as a result, the capacitance of the unit [2221]. The sensor is capable of both µmol/mol and dew point measurements in most industrial gas streams, including hydrogen. Examples of aluminum oxide moisture sensors for hydrogen matrix are the MM300 [2827] and MM400 systems from Systech Illinois [2726], the AquaXact 1688 from Servomex [2928], and the IQ probe [3029] and HygroPro [3130] from General Electric.

2.4. Chilled-Mirror Hygrometer

Chilled-mirror hygrometers operate by directly measuring the dew-point temperature (the temperature to which a volume of gas must be cooled at constant pressure to become saturated with water vapor) of a gas stream [2221]. Consequently, any cooling below the dew-point temperature causes the excess water to condense, and this can then be detected optically on a mirror surface. Since the dewpoint temperature is a fundamental thermodynamic property, chilled-mirror hygrometry is considered an absolute measurement method and is also used widely as a calibration and transfer standard. However, it seems that the costs for this technology is above the target of 5000 euros. Examples of chilled-mirror hygrometers for hydrogen matrix are the Cong Prima 2M [3231], the FAS-W [3332], and the Hygrovision [3433] from Vympel.

2.5. Surface Acoustic Wave

Ball Wave Inc. has developed a moisture analyzer based on the principle of non-diffraction propagation of surface acoustic waves (SAWs). The sensor [3534] consists of a spherical single-crystal α-quartz which is a piezoelectric material that converts electrical signals to mechanical vibrations and vice versa. Electrodes are manufactured on the surface of the sensor by depositing a metal thin film called an interdigital transducer (IDT). When electrical signals are fed into the IDT, a mechanical vibration, called a Rayleigh wave, is generated and propagates along the surface. A thin layer of amorphous silica deposited on the ball SAW sensor has an ability to absorb and desorb water molecules. The amount of water molecules contained in a gas can be estimated by measuring the changes either in the velocity or in the attenuation of the Rayleigh wave propagating around the surface of the ball SAW sensor.

2.6. Chemical Optical Sensor

The principle of a chemical-optical sensor is based on the effect of dynamic luminescence quenching by molecular oxygen. Quenching refers to any process which decreases the fluorescence intensity of a given substance. The collision between the luminophore in its excited state and the quencher (oxygen) results in radiationless deactivation. After collision, energy transfer takes place from the excited indicator molecule to oxygen which consequently is transferred from its ground state (triplet state) to its excited singlet state. As a result, the indicator molecule does not emit luminescence and the measurable luminescence signal decreases. PreSens has developed oxygen sensors based on this principle which have a detection limit of 0.5 µmol/mol [3635].

2.7. Proton Exchange Membrane Type Sensor

The concept of Proton Exchange Membrane (PEM) type sensors is being tested by Los Alamos National Laboratory as part of a project having as scope to develop a device using a membrane electrode assembly to measure impurities in a dry fuel stream of hydrogen at and above the SAE J2719 levels [87] with a quick response (t < 5 min). A Nafion based electrochemical hydrogen contaminant detector was tested at a HRS in Burbank, USA with promising results (effective detection of CO down to 1 µmol/mol). To the authors' knowledge, none of these sensors are yet commercially available. The sensitivity for 200 nmol/mol carbon monoxide in dry hydrogen of these types of sensors has been demonstrated [3736].

2.8. Analysers

There are many other analytical principles to detect impurities, such as water, hydrocarbons, oxygen, helium, nitrogen, argon, carbon dioxide, carbon monoxide, ammonia, formaldehyde, formic acid, total sulfur compounds, and halogenated compounds in hydrogen matrix. Examples of those are spectrometry laser photoacoustic, tunable diode laser absorption spectroscopy, Fourier transformed infrared spectroscopy, cavity ring-down spectroscopy, optical feedback cavity enhanced absorption spectroscopy, broadly tunable laser technique, tunable diode laser, etc. These methods are considered here as belonging to the category of gas analyzers; however, the classification of sensors or analyzers is not always clearly defined and described in detail. Information about all these methods can be found in a report recently written as part of the European project “MetroHyVe2” [3837].

2.9. Sensors Overview for Hydrogen Fuel Quality

The information about the sensors described in the previous sections is summarized in Table 1. The table just shows the sensors that have been identified so far however, other sensors (with the same technology or other technologies) are probably available as well as other sensors manufacturers.
Table 1.
Information about available sensors for impurities in hydrogen classified by technologies.
Technology Supplier (Compound) Model Response Time

(T90)		 Selectivity Sensitivity/Range Stability Temperature Range (°C) Pressure Range (bar) Flow Rate Costs
Electrochemical sensor DSK GmBH (O2) OxyTransII or Oxymaster II <45 s n.c. n.c. n.c. 0 to 50 0.1 to 1 n.c. +
Southland Sensing Ltd. (O2) TO2-133 7 s n.c. O2: 0 to 10 µmol/mol No info 0 to 50 n.c. 15–150 l/h ++
Systech Illinois (O2) EC91 20 s n.c. O2: 1 to 20 µmol/mol No info 0 to 40 0.1 to 1, up to 17 with optional sample system 1.8 to 300 l/h 0
Chemical-optical sensor Presens (O2) Oxy-1 SMA-trace-RS232 n.c. n.c. O2: down to 0.5 µmol/mol n.c. n.c. n.c. n.c. +
Phosphorus pentoxide moisture sensor DKS (H2O) Aquatrace IV Dry to wet: <5 s

Wet to dry <15 min		 <10 µmol/mol H2S H2O: 0.05 to 2000 µmol/mol n.c. 5 to 65 Approx 0.2 above the measuring cell inlet 20 or 100 Nl/h +
DSK GmBH (H2O) Aquatrace ATT500 Dry to wet: <5 s

Wet to dry <15 min		 Not compatible with ammonia H2O: 0 to 500 µmol/mol n.c. −10 to 60 0–20 1–300 Nl/h +
Systech Illinois (H2O) MM50 Within 60 s n.c. H2O: 0.1 to 1000 µmol/mol No info n.c. n.c. n.c. n.c.
MEECO (H2O) Uber M-I 5 min   H2O: 0.5 to 5000 µmol/mol   0 to 60 0.2 to 7   +
Systech Illinois (H2O) MM300 <5 min Annual calibration recommended Dewpoint: −100 to 20 °C No compatible with HCl, NH3, Cl2 −40 to 60 450 30 to 420 Nl/h +
Dr. Wernecke (H2O) Humitrace II     H2O:0 to 2000 µmol/mol n.c. 5 to 65 1 to 5 20 Nl/h, 100 Nl/h  
Chilled mirror Vympel (H2O) Cong Prima 2M 5–15 min (0.3–2 Nl/min) “No drift” Dewpoint: −30 to 30 °C n.c. n.c. 160–300 0.3 to 2 Nl/min 00
Vympel (H2O) FAS 5–15 min n.c. Dewpoint: −80 to 60 °C (3 different ranges) n.c. −20 to 80 <100 0.2 to 2 Nl/min 00
Vympel (H2O) Hygrovision n.c. n.c. Dewpoint: −50 to 30 °C n.c. −10 to 50 <100 0.2 to 2 Nl/min  
Baker Hughes (H2O) Optica n.c. n.c. Dewpoint: −80 to 15 °C (1311-XR) n.c. 0 to35 1 to 8 0.25 to 2.5 l/min 00
Metal oxide dew-point Vympel (H2O) FAS-SW n.c. n.c. Dewpoint: −100 to 20 °C

(2 different ranges)		 n.c. −40 to 60 <300 0.5 to 5 Nl/min  
Baker Hughes (H2O) HygroPro 15 s n.c. Dewpoint: −110 to 20 °C n.c. −20 to 60 to 345 n.c. +
Baker Hughes (H2O)

(aluminum oxide)		 M Series Probe n.c. n.c. Dewpoint: −110 to 60 °C overall in 3 ranges (ex: −110 to −50 °C) n.c. 0 to 60 <0.01 to 345 n.c. n.c.
Servomex (H2O) Aquaxact 1688 n.c. n.c. Dewpoint: −100 to 20 °C n.c. n.c. n.c. n.c. n.c.
Surface Acoustic wave Ball Wave (H2O) FT-300WT <1 s n.c. H2O: 1–4000 µmol/mol n.c. 10–40 Atmospheric pressure 0–1 l/min 0
n.c.: information not available or not communicated; The prices are indicated by ranges; ++: < 1000€; +: 1000–5000€; 0: 5001–10,000€; 00: >10,000€.
 

3. Conclusions

Hydrogen is receiving serious consideration as an alternative energy source. FCEVs are fully carbon dioxide emission free, but their deployment in the daily life requires the development of a refueling infrastructure. As for all technologies, there is a need of minimizing potential issues that could lower the general acceptance for this market. Sensor technology can ensure the safe and efficient implementation of the emerging global hydrogen market. Chemical sensors which respond to a particular analyte in a selective and reversible way could be used to indicate the presence of impurities harmful for the fuel cell system allowing the HRS to take rapid actions.
Only a few sensors with the required specifications have been found, showing there is a need to develop sensors specifically for the hydrogen industry. Several sensors for detecting oxygen and water have been identified, and different principles of measurement allow the detection of low µmol/mol for these two species in hydrogen. Sensors for other compounds, such as carbon monoxide, carbon dioxide, methane, hydrogen sulfide, ammonia, formaldehyde, formic acid, and hydrocarbons, seem to not yet be available at the target costs (5000 euros). To the cost of the sensing element itself, it is usually necessary to add costs for complementary components/spare parts (such as temperature probe, gas sampling system, etc.).
For economical and safety reasons, there is a need to test sensors first in an exposure chamber (laboratory testing) and then at a HRS. But there is currently a lack of testing capability, and support (time and investment) should be provided to develop facilities, such as the SSTUF, with the ability to test under these relatively harsh conditions. However, it will first require the development of standardized testing protocols and targets for the metrics. Here, a similar approach to the one undertaken by EPA for air sensor is recommended.
Based on the sensor unavailability and current cost, it will be necessary to first establish the industrial needs for these sensors before a development is conceivable. Therefore, the development of a discussion platform between sensor providers and the hydrogen industry may be relevant to share information, discuss research and development requirements, and encourage a better collaboration between both parts.

References

  1. H2GreenTECH. A Hydrogen Strategy for a Climate-Neutral Europe. Available online: https://www.h2greentech.eu/ (accessed on 10 November 2021).
  2. National Hydrogen Strategies—An Update on Recent Progress in the Hydrogen Markets. Available online: https://home.kpmg/xx/en/home/insights/2021/08/national-hydrogen-strategies.html (accessed on 10 November 2021).
  3. IEA. The Future of Hydrogen. Available online: https://www.iea.org/reports/the-future-of-hydrogen (accessed on 10 November 2021).
  4. Hübert, T.; Brett, L.; Buttner, W. Sensors for Safety and Process Control in Hydrogen Technologies; CRC Press: Boca Raton, FL, USA, 2015.
  5. Buttner, W.; Rivkin, C.; Burgess, R.; Weidner, E.; Brett, L.; Hübert, T. Role of Sensors for Safe H2 Deployment. 2014. Available online: http://www.hysafe.info/wp-content/uploads/2016/07/568_RPW2014_Presentations-Research-Priorities-2014-distribution-updated-2016-05-20.pdf (accessed on 10 November 2021).ISO 14687:2019—Hydrogen Fuel Quality—Product Specification; International Organization for Standardization: Geneva, Switzerland, 2019.
  6. ISO 14687:2019—Hydrogen Fuel Quality—Product Specification; International Organization for Standardization: Geneva, Switzerland, 2019.EN 17124:2018—Hydrogen Fuel—Product Specification and Quality Assurance—Proton Exchange Membrane (PEM) Fuel Cell Applications for Road Vehicles; European Committee for Standardization: Brussels, Belgium, 2018.
  7. EN 17124:2018—Hydrogen Fuel—Product Specification and Quality Assurance—Proton Exchange Membrane (PEM) Fuel Cell Applications for Road Vehicles; European Committee for Standardization: Brussels, Belgium, 2018.Hydrogen Fuel Quality for Fuel Cell Vehicles J2719_201109; SAE International: Warrendale, PA, USA, 2011.
  8. Hydrogen Fuel Quality for Fuel Cell Vehicles J2719_201109; SAE International: Warrendale, PA, USA, 2011.ISO 19880-8:2019—Gaseous Hydrogen—Fuelling Stations—Part 8: Fuel Quality Control; International Organization for Standardization: Geneva, Switzerland, 2019.
  9. ISO 19880-8:2019—Gaseous Hydrogen—Fuelling Stations—Part 8: Fuel Quality Control; International Organization for Standardization: Geneva, Switzerland, 2019.Wen, W. Introductory chapter: What is chemical sensor? In Progresses in Chemical Sensor; InTechOpen: London, UK, 2016.
  10. Wen, W. Introductory chapter: What is chemical sensor? In Progresses in Chemical Sensor; InTechOpen: London, UK, 2016. Spinelle, L.; Gerboles, M.; Aleixandre, M. Performance evaluation of amperometric sensors for the monitirong of O2 and NO2 in ambient air at ppb level. Procedia Eng 2015, 120, 480–483.
  11. Spinelle, L.; Gerboles, M.; Aleixandre, M. Performance evaluation of amperometric sensors for the monitirong of O2 and NO2 in ambient air at ppb level. Procedia Eng 2015, 120, 480–483. Popoola, O.; Stewart, G.; Mead, M.; Jones, R. Development of a baseline-temperature correction methodology for electrochemical sensors and its implications for long-term stability. Atmos. Environ. 2016, 147, 330–343.
  12. Popoola, O.; Stewart, G.; Mead, M.; Jones, R. Development of a baseline-temperature correction methodology for electrochemical sensors and its implications for long-term stability. Atmos. Environ. 2016, 147, 330–343. Air Sensor Performance Targets and Testing Protocols. 2021. Available online: https://www.epa.gov/air-sensor-toolbox/air-sensor-performance-targets-and-testing-protocols (accessed on 10 November 2021).
  13. Air Sensor Performance Targets and Testing Protocols. 2021. Available online: https://www.epa.gov/air-sensor-toolbox/air-sensor-performance-targets-and-testing-protocols (accessed on 10 November 2021).Cebolla, R.O.; Weidner, R.; Buttner, W.; Bonato, C. Summary report for a hydrogen sensor workshop, Hydrogen safety sensors and their use in application with hydrogen as an alternative fuel. In JRC Conference and Workshop Reports, National Renewable Energy Laboratory; Publications Office of the European Union: Luxembourg, 2017.
  14. Cebolla, R.O.; Weidner, R.; Buttner, W.; Bonato, C. Summary report for a hydrogen sensor workshop, Hydrogen safety sensors and their use in application with hydrogen as an alternative fuel. In JRC Conference and Workshop Reports, National Renewable Energy Laboratory; Publications Office of the European Union: Luxembourg, 2017. Duvall, R.M.; Clement, A.L.; Hagle, G.; Kamal, A.; Kilaru, V. Performance Testing Protocols, Metrics, and Target Values for Ozone Air Sensors; U.S. Environmental Protection Agency: Washington, DC, USA, 2021.
  15. Duvall, R.M.; Clement, A.L.; Hagle, G.; Kamal, A.; Kilaru, V. Performance Testing Protocols, Metrics, and Target Values for Ozone Air Sensors; U.S. Environmental Protection Agency: Washington, DC, USA, 2021.Metrology for Hydrogen Vehicles. Available online: https://www.metrohyve.eu/ (accessed on 28 April 2021).
  16. Metrology for Hydrogen Vehicles. Available online: https://www.metrohyve.eu/ (accessed on 28 April 2021).Technical Specifications for CO-B4 Carbon Monoxide Sensore. Available online: https://www.alphasense.com/WEB1213/wp-content/uploads/2019/09/CO-B4.pdf (accessed on 16 April 2021).
  17. Technical Specifications for CO-B4 Carbon Monoxide Sensore. Available online: https://www.alphasense.com/WEB1213/wp-content/uploads/2019/09/CO-B4.pdf (accessed on 16 April 2021).Aleixandre, M.; Gerboles, M. Review of small commercial sensors for indicative monitoring of ambient gas. Chem. Eng. Trans. 2012, 30, 169–174.
  18. Aleixandre, M.; Gerboles, M. Review of small commercial sensors for indicative monitoring of ambient gas. Chem. Eng. Trans. 2012, 30, 169–174. Southland Sensing Ltd. Southland Sensing O2 Sensors (Gas). Available online: http://www.sso2.com/products/industrial-oxygen-sensors (accessed on 16 March 2021).
  19. Southland Sensing Ltd. Southland Sensing O2 Sensors (Gas). Available online: http://www.sso2.com/products/industrial-oxygen-sensors (accessed on 16 March 2021).EC91 ATEX O2 Analyzers. Systech Illinois. 2021. Available online: https://www.systechillinois.com/en/products/ec91-safe-oxygen-analyser (accessed on 10 November 2021).
  20. EC91 ATEX O2 Analyzers. Systech Illinois. 2021. Available online: https://www.systechillinois.com/en/products/ec91-safe-oxygen-analyser (accessed on 10 November 2021).Oxygen Measurements. DKS GmbH. Available online: https://www.dks-engineering.com/en/products-gas-measurement-and-process-measurements-and-data-visualization/oxygen-measurements-with-zirox/143-oxytrans-ii-ex (accessed on 16 March 2021).
  21. Oxygen Measurements. DKS GmbH. Available online: https://www.dks-engineering.com/en/products-gas-measurement-and-process-measurements-and-data-visualization/oxygen-measurements-with-zirox/143-oxytrans-ii-ex (accessed on 16 March 2021).Raynor, M.W.; Bertness, K.A.; Cossel, K.C.; Adler, F.; Ye, J. Trace water vapor analysis in speciality gases: Sensor and spectroscopuc approaches. In Trace Analysis of Specialty and Electronic Gases; Wiley: Hoboken, NJ, USA, 2013.
  22. Raynor, M.W.; Bertness, K.A.; Cossel, K.C.; Adler, F.; Ye, J. Trace water vapor analysis in speciality gases: Sensor and spectroscopuc approaches. In Trace Analysis of Specialty and Electronic Gases; Wiley: Hoboken, NJ, USA, 2013. Systech Illinois. P205 Phosphorous Pentoxide Moisture SensorTechnology for Our Moisture Analyzers. Available online: https://www.systechillinois.com/en/support/technologies/p205-moisture-sensor (accessed on 17 March 2021).
  23. Systech Illinois. P205 Phosphorous Pentoxide Moisture SensorTechnology for Our Moisture Analyzers. Available online: https://www.systechillinois.com/en/support/technologies/p205-moisture-sensor (accessed on 17 March 2021).AQUATRACE® Transmitter ATT500. Available online: https://www.dks-engineering.com/en/news/156-finally-here-is-our-new-version-of-aquatrace-transmitter-att500 (accessed on 17 March 2021).
  24. AQUATRACE® Transmitter ATT500. Available online: https://www.dks-engineering.com/en/news/156-finally-here-is-our-new-version-of-aquatrace-transmitter-att500 (accessed on 17 March 2021).Uber M-I Family. Available online: https://meeco.com/meeco/wp-content/themes/mecco/pdf/english/M-i.pdf (accessed on 17 March 2021).
  25. Uber M-I Family. Available online: https://meeco.com/meeco/wp-content/themes/mecco/pdf/english/M-i.pdf (accessed on 17 March 2021).Wernecke, R. Trace Humidity in Gases; Posdam, Germany, 2016; Available online: https://www.researchgate.net/publication/318014701_Trace_humidity_in_gases (accessed on 10 December 2021).
  26. Wernecke, R. Trace Humidity in Gases; Posdam, Germany, 2016; Available online: https://www.researchgate.net/publication/318014701_Trace_humidity_in_gases (accessed on 10 December 2021).Systech Illinois. Moisture Analyzer MM400. Available online: https://www.systechillinois.com/en/products/mm400-moisture-analyzer (accessed on 17 March 2021).
  27. Systech Illinois. Moisture Analyzer MM400. Available online: https://www.systechillinois.com/en/products/mm400-moisture-analyzer (accessed on 17 March 2021).Systech Illinois. Moisture Transducer MM300 for Moisture Measurement. Available online: https://www.systechillinois.com/en/products/mm300-moisture-transducer (accessed on 28 April 2021).
  28. Systech Illinois. Moisture Transducer MM300 for Moisture Measurement. Available online: https://www.systechillinois.com/en/products/mm300-moisture-transducer (accessed on 28 April 2021).The AquaXact 1688 Is a Fast, Accurate Moisture Sensor. Available online: https://www.servomex.com/gas-analyzers/finder/aquaxact-1688/ (accessed on 17 March 2021).
  29. The AquaXact 1688 Is a Fast, Accurate Moisture Sensor. Available online: https://www.servomex.com/gas-analyzers/finder/aquaxact-1688/ (accessed on 17 March 2021).IQ.Probe—Aluminum Oxide Moisture Probe. Available online: https://dam.bakerhughesds.com/m/2e5411879c5fbe52/original/IQ-probe-Aluminum-Oxide-Moisture-Probe_CS-pdf. (accessed on 17 March 2021).
  30. IQ.Probe—Aluminum Oxide Moisture Probe. Available online: https://dam.bakerhughesds.com/m/2e5411879c5fbe52/original/IQ-probe-Aluminum-Oxide-Moisture-Probe_CS-pdf. (accessed on 17 March 2021).HygroPro Aluminum Oxide Moisture Transmitter. Available online: https://www.bakerhughesds.com/sites/g/files/cozyhq596/files/2020-01/920-145e_a4.pdf (accessed on 17 March 2021).
  31. HygroPro Aluminum Oxide Moisture Transmitter. Available online: https://www.bakerhughesds.com/sites/g/files/cozyhq596/files/2020-01/920-145e_a4.pdf (accessed on 17 March 2021).Gas Quality Analyzer CONG PRIMA-2M (Flow-Through Submersible Design). Available online: http://en.vympel.group/products/gas-analyzers/kong-prima-2m-protok-inner/ (accessed on 28 April 2021).
  32. Gas Quality Analyzer CONG PRIMA-2M (Flow-Through Submersible Design). Available online: http://en.vympel.group/products/gas-analyzers/kong-prima-2m-protok-inner/ (accessed on 28 April 2021).FAS-W Humidity Analyzer. Available online: http://en.vympel.group/products/gas-analyzers/analizator-vlazhnosti-fas-w/ (accessed on 28 April 2021).
  33. FAS-W Humidity Analyzer. Available online: http://en.vympel.group/products/gas-analyzers/analizator-vlazhnosti-fas-w/ (accessed on 28 April 2021).The HYGROVISION-BL Dew Point Analyzer. Available online: http://en.vympel.group/products/gas-analyzers/hygrovision-bl/ (accessed on 28 April 2021).
  34. The HYGROVISION-BL Dew Point Analyzer. Available online: http://en.vympel.group/products/gas-analyzers/hygrovision-bl/ (accessed on 28 April 2021).Takeda, N.; Carroll, P.; Tsukahara, Y.; Beardmore, S.; Bell, S.; Yamanaka, K.; Akao, S. Trace moisture measurement in natural gas mixtures with a single calibration for nitrogen background gas. Meas. Sci. Technol. 2020, 31, 104007.
  35. Takeda, N.; Carroll, P.; Tsukahara, Y.; Beardmore, S.; Bell, S.; Yamanaka, K.; Akao, S. Trace moisture measurement in natural gas mixtures with a single calibration for nitrogen background gas. Meas. Sci. Technol. 2020, 31, 104007. PreSens. Compact Trace Oxygen Meter with Analog Output. Available online: https://www.presens.de/products/detail/oxy-1-sma-trace-rs232-ao (accessed on 18 March 2021).
  36. PreSens. Compact Trace Oxygen Meter with Analog Output. Available online: https://www.presens.de/products/detail/oxy-1-sma-trace-rs232-ao (accessed on 18 March 2021).Rockward, T.; Brosha, E.; Lujan, R.; Mukundan, R.; Romero, C.; Williams, S.; Wilson, M. Codes & Standards Tech Team Update: Fuel Quality Analyzer; Los Alamos National Laboratories: Los Alamos, NM, USA, 2017.
  37. Rockward, T.; Brosha, E.; Lujan, R.; Mukundan, R.; Romero, C.; Williams, S.; Wilson, M. Codes & Standards Tech Team Update: Fuel Quality Analyzer; Los Alamos National Laboratories: Los Alamos, NM, USA, 2017.Arrhenius, K.; Bacquart, T. A2.4.1: Review of the state of the art of online gas sensors/analysers. In MetroHyVe2; 2021; Available online: https://www.sintef.no/projectweb/metrohyve-2/downloads/ (accessed on 10 December 2021).
  38. Arrhenius, K.; Bacquart, T. A2.4.1: Review of the state of the art of online gas sensors/analysers. In MetroHyVe2; 2021; Available online: https://www.sintef.no/projectweb/metrohyve-2/downloads/ (accessed on 10 December 2021).
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)
Video Production Service
Feedback