Sensors for the detection of hydrogen, which is very volatile, extremely flammable and highly explosive, are needed in many fields, for example in nuclear power plants, in launch vehicles for human space flight, in hydrogen production plants, and fuel cells. To enhance the safety level it seems appropriate to use optical sensors instead of electronic ones.
In the presentation, investigations concerning the use of fiber optic Bragg grating (FBG) sensors as part of the surveillance system of liquid fuel tanks will be described. The sensors are supposed to measure strain and temperature when embedded in the inner tank wall and to detect hydrogen leakage. To fulfill this task the temperature and strain sensors have to prove their functionality down to minimum temperatures of 20K.
As the dn/dT for quartz decreases to very low values, the FBG temperature transducer has to be bonded to a substrate with sufficiently high coefficient of thermal expansion also under cryogenic conditions. As the only applicable solution a high-expansion glass has been found, which in connection with specific fiber coating and bonding materials for the strain-transducer fulfils all the sensor requirements.
The hydrogen sensor utilizes the expansion of palladium in an atmosphere containing hydrogen and consists in our new sensor configuration of a palladium foil bonded to a special-shaped fiber. Experimental results for concentration ranges 0-4%vol H2 and temperature ranges from -40°C to +80°C show the parameters of application of a hydrogen leakage detection system.