Resonant transducers are used in a number of applications e.g. for the measurement of temperature or pressure. These devices are maintained in a state of resonance by the application of drive signals of appropriate frequency and phase. Conventionally the drive is applied as an electrical signal. When the transducer is to be used in a hazardous enviroment it is clearly desirable to avoid the use of electrical connections. Optical coupling to and from a transducer is inherently safe. However, optical coupling introduces the problems of providing drive signals to the transducer to maintain oscillation.
The object of the invention is to minimise or to overcome the disadvantage.