Microwave electronic load measuring system

Abstract

An electronic weighing system is disclosed which, employs spaced cylindrical dielectric rings as the load measuring transducer. A support structure is provided to linearly vary the spacing between the rings responsive to applied load which will linearly vary the resonant frequency of the rings. In an active mode, each microwave load cell is excited by an unstable oscillator, the dielectric rings stabilizing the oscillator at a resonant frequency which is proportional to their spacing. The oscillation frequency of the load cell is measured and used to compute the magnitude of the load applied to the cell based upon a predetermined relationship between output frequency and load. A plurality of multiplexed load cells may be employed. In a passive mode, a voltage controlled oscillator generates a microwave signal which linearly sweeps a preset frequency band. The sweeping signal is applied across the dielectric rings which generate a detectable pulse at their primary resonant frequency. The pulse is detected and the resonant frequency at which the pulse was generated is determined. The applied load is calculated from the resonant frequency and routed to a display panel. In a temperature compensation embodiment, a temperature sensor generates a voltage output which is converted to an RF signal and modulated onto the microwave oscillator output.