A7. Introduction
There are several types of hydrogen sensors depending on its intended use. The electrochemical, catalytic and thermal conductivity detectors (TCD) are mainly used in the industries where the hydrogen risk is present. The metal oxide semi-conductor-based sensor (MOS) is most often used in research laboratories, whereas the MEMS (micro-electro-mechanic system) are used in the aeronautic and aerospace industries. Other less common but still commercially available sensors include gas field effect (GFE) type sensors and acoustic sensors. The various types of hydrogen detection technologies currently in use are described in detail in Chapter 5 of the HySafe Biennial Report on Hydrogen Safety (BRHS) [1] together with a description of emerging technologies for hydrogen detection.
Some important factors to consider in the selection of a hydrogen sensor include accuracy, measuring range, response time, ambient working conditions, lifetime and stability (ISO/TR15916) [2]. A market investigation on the performance of commercially available sensors has been performed (HYSAFE D5.4 [3]); the investigation was based on the technical information (product specifications, datasheets) made available by manufacturers.
Some general hydrogen performance targets for hydrogen safety sensors are given below [4]:
- Measurement range:0.1–10% H2 in air
- Operating temperature: -30–+80 °C
- Humidity range: 10-98%
- Response time: t[90] < 1 sec
- Accuracy: 5%
- Lifetime: 5 yrs
Considering these performance targets and the capabilities of commercially available hydrogen detection systems shortcomings of current detection techniques are highlighted in Table 1.
Table 1 Indications where commercially available sensors meet or fail to meet current performance targets
| Criteria | Target | Electrochem | Catalytic | MOS | Acoustic | TCD | GFE | |||||||||
| Measuring Range % | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | ||
| 0.1 | 10 | v | x | v | x | v | x | v | v | v | v | v | x | |||
| Temperature Range / °C | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | ||
| -30 | +80 | x | x | x | x | v | v | x | v | v | x | v | v | |||
| Humidity Range %RH | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | ||
| 10 | 98 | v | x | v | v | v | v | v | v | v | v | v | x | |||
| Response Time t[90] / s | <1 | x | x | x | v | x | x | |||||||||
| Accuracy % | 5 | - | v | x | x | v | - | |||||||||
| Lifetime / yrs | 5 | x | v | v | v | v | - | |||||||||
Due to the considerable differences in the various requirements for indoor applications, no sensor type is currently capable of meeting all performance target sets. Each detection technology has advantages and disadvantages depending on its intended application. When considering a hydrogen detector for a particular application, the desired performance capabilities and ambient conditions for the application should be considered.