Method and apparatus for detecting the position of a piston of a piston cylinder through the use of microwaves

摘要

A method for detecting the position of a piston of a piston cylinder is provided. A microwave transmit signal is emitted in the direction of the piston and microwaves reflected from the piston are detected. The transmit signal is a modulated signal with a base frequency sinusoidally modulated at a modulation frequency. An evaluation of the phase between transmit signals and receive signals is performed. A phase determination at the baseband and a simultaneous phase determination at at least one sideband are also performed. The phase determination at the baseband is used for fine determination of the piston position and the phase determination at the at least one sideband is used for coarse determination of the piston position. Bandpass filtering on receive signals and evaluation transmit signals is performed with respect to the base frequency or an intermediate frequency. Bandpass filtering is performed with respect to the modulation frequency.

主权项

1. Method for detecting the position of a piston of a piston cylinder, comprising:
emitting microwave transmit signals in a direction of the piston and detecting microwaves reflected from the piston in receive signals; the transmit signals comprising modulated signals which have a base frequency sinusoidally modulated at a modulation frequency; performing an evaluation of a phase difference between evaluation transmit signals and the receive signals, the evaluation transmit signals corresponding in their characteristics to the transmit signals; performing a determination of the phase difference between the evaluation transmit signals and the receive signals at a baseband and a simultaneous determination of the phase difference between the evaluation transmit signals and the receive signals at at least one sideband; using the phase difference at the baseband for a fine determination of the piston position and the phase difference at the at least one sideband for a coarse determination of the piston position; bandpass filtering the receive signals and the evaluation transmit signals with respect to the base frequency or an intermediate frequency; and bandpass filtering the receive signals and the evaluation transmit signals with respect to the modulation frequency; wherein a phase of the modulated signal is of the form
φT=2πf0t+η sin(2πfmt−φm0)where f0 is the base frequency, fm is the modulation frequency, η is a modulation index and φm0 is a constant.