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Concept
Hydrogen sensor
Summary
A hydrogen sensor is a gas detector that detects the presence of hydrogen. They contain micro-fabricated point-contact hydrogen sensors and are used to locate hydrogen leaks. They are considered low-cost, compact, durable, and easy to maintain as compared to conventional gas detecting instruments.
There are five key issues with hydrogen detectors:
Reliability: Functionality should be easily verifiable.
Performance: Detection 0.5% hydrogen in air or better
Response time < 1 second.
Lifetime: At least the time between scheduled maintenance.
Cost: Goal is 30 per controller.
Measurement range coverage of 0.1–10.0% concentration
Operation in temperatures of −30 °C to 80 °C
Accuracy within 5% of full scale
Function in an ambient air gas environment within a 10–98% relative humidity range
Resistance to hydrocarbon and other interference.
Lifetime greater than 10 years
There are various types of hydrogen microsensors, which use different mechanisms to detect the gas. Palladium is used in many of these, because it selectively absorbs hydrogen gas and forms the compound palladium hydride. Palladium-based sensors have a strong temperature dependence which makes their response time too large at very low temperatures. Palladium sensors have to be protected against carbon monoxide, sulfur dioxide and hydrogen sulfide.
Several types of optical fibre surface plasmon resonance (SPR) sensor are used for the point-contact detection of hydrogen:
Fiber Bragg grating coated with a palladium layer – Detects the hydrogen by metal hindrance.
Micromirror – With a palladium thin layer at the cleaved end, detecting changes in the backreflected light.
Tapered fibre coated with palladium – Hydrogen changes the refractive index of the palladium, and consequently the amount of losses in the evanescent wave.
Electrochemical hydrogen sensor – low (ppm) levels of hydrogen gas can be sensed using electrochemical sensors which comprise an array of electrodes packaged so as to be surrounded by a conductive electrolyte and gas ingress controlled with a diffusion limited capillary.
Official source
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