US Patent 7299678 Sensor apparatus

A measurement head particularly for borehole use can measure multiple parameters with no electronics in the head and only a single conductor cable. Double-ended tuning forks (26, 28 and 38, 40) in the head are arranged to respond to different parameters such as temperature and pressure by adjusting their resonant frequencies. A drive signal on the conductor (50) is applied to transducers (30, 32, 42, 44) on all the tuning forks and those whose instantaneous resonant frequency is close will resonate. The signal is removed and the transducers return a decaying signal at the resonant frequency along the conductor. Other drive frequencies are tried, to locate the other sensors whose frequency ranges are separate.