Gap discharge transducers applied to ultrasonic flow measurement

Sammanfattning: In this thesis, the potential of the gap discharge transducer is investigated as both a sound pulse emitter and a sound pulse receiver in a gas flow measurement setup. The main objective is to use the gap discharge transducer as an integral part in a gas flow measurement system developed for harsh environments. The idea for the method considered in this study to determine the flow was taken from the time-of-flight technique used in ultrasonic flow measurements. The gap discharge transducer should then be used as both an emitter and a receiver in a setup that somewhat mimics those in ultrasonics. Earlier studies with the gap discharge transducer has shown that it is both very durable and a potent sound pulse emitter. This thesis continues these studies by incorporating the transducer into a measurement system as an emitter and also investigates its capabilities to be used as a sound pulse receiver. As an emitter in a flow measurement system the transducer was placed in a pipe with a variable flow in a laboratory environment. The transducer was set to generate sparks to create the sound pulse and standard piezoelectric receivers were used to capture the signal. To determine the possibilities to use the transducer as a receiver the transducer was placed in a vacuum chamber to test the dependence between breakdown voltage and pressure. Since a sound pulse is a change in pressure the pulse might cause breakdown in the gap between the electrodes of the transducer if an initial voltage between the electrodes is set close enough to breakdown. The investigation shows that the gap discharge transducer is a potential sound pulse emitter in a flow measurement system and, with some small calibration and more precise alignment, is capable to determine the flow quite accurately. On the other hand, to use the transducer as a receiver is concluded to be very difficult. The breakdown voltage is too unstable to allow an initial voltage close to breakdown to be set without risking spontaneous breakdown due to random events.