A Precision Pressure Tranducer with FM Output in UHF Band

This paper describes a novel pressure transducer (10,000 psi) with a frequency output of 500 MHz at zero pressure and 455 Mhz at full-scale. This sensitivity is achieved at a stress level of 20 per cent of the elastic limit yielding very low errors due to hysterisis and elastic creep. The transducer consists of two concentric tubes long, electron-beam welded at each end. A short section at the center of the outer tube is reduced in diameter to form an annular gap of the inner tube expands its diameter, reduces the gap and increases the capacitance in parallel with the inductance formed by the concentric tubes. The resulting resonant circuit is used to control the frequency of a single transistor oscillator. The very high Q of the circuit (1500) results in excellent frequency stability.