Velocity measurement system with synchronized demodulation

Claim 2

In a system having an input signal varying in dynamic phase relation from a substantially synchronous reference signal, wherein the dynamic phase change relation varies in a phase retarding or a phase advancing sense, the method of providing a conditioned output signal to meet the requirement of having a positive-going value for a selected sense of phase of said input signal, and a negative-going value for the opposite sense of phase change of said input signal, comprising the steps of: modifying said reference signal by generating from it two synchronous reference components having a mutual phase difference of approximately 90*; synchronously demodulating said input signal with reference to said synchronous reference components to provide first and second output signals having amplitudes respectively sine and cosine functions of the phase angle between said input signal and said reference signal; inverting said output signals to provide third and fourth output signals of opposite respective polarity, comparing the four output signals in groups of threes to identify which signal of the four has an instantaneous value and polarity to meet said conditioned output requirement, and switching the identified said signal to a useful output.

Claim 3

The method as claImed in claim 1 wherein said reference signal and said input signal originate with a common oscillator, said input signal being transduced to an ultrasonic signal, said ultrasonic signal being transmitted transversely through a flowing stream to produce modulation of the signal, being then reconverted by transducer to an electrical signal having a differing phase relation with said reference signal.

Claim 4

The method as claimed in claim 2 wherein said conditioned and identified signal is amplified for passage to an output.

Claim 5

The method as claimed in claim 3 wherein said amplified signal is submitted, together with a corresponding signal from a location spaced along the stream, to a cross-correlation analysis whereby the two signals are correlated to establish the time delay of correlatable components of the signals from the two locations as an accurate measure of stream speed of flow.

Claim 6

A signal modulation detection system to provide conditioned output signal voltage to meet the requirement of having a positive-going value for a selected sense of phase change of an input signal and a negative-going value for the opposite sense of phase change of an input signal corresponding to a change in phase modulation of the input signal characteristic and substantially insensitive to changes in amplitude modulation of the input signal, comprising a source of synchronizing reference signals; phase change means connected thereto having a first output to provide a phase advanced synchronous signal component and a second output to provide a phase retarded synchronous signal component, said advanced and retarded reference components having a mutual phase difference of approximately 90*; amplifier means to receive a said modulated input signal, having the output thereof connected to a pair of synchronous demodulators, each said demodulator receiving a respective one of said advanced or retarded reference signal components, the output from each said demodulator being connected with an inverter means, the output from the two inverters together with the output from the two demodulators comprising four outputs having separate signals mutually separated in phase approximately 90*, 180* and 270* selection means connected with said four outputs to identify the one of said signals in accordance with the desired conditioned characteristic, and switching means operated by said selection means to switch said desired conditioned signal to an output amplifier.

Claim 7

A signal modulation detection system to provide conditioned output signal voltage to meet the requirement of having a positive-going value for a selected sense of phase change of an input signal and a negative-going value for the opposite sense of phase change of an input signal corresponding to a change in phase modulation of the input signal characteristic and substantially insensitive to changes in amplitude modulation of the input signal, comprising a source of synchronizing reference signals; phase change means connected thereto having a first output to provide a phase advanced synchronous signal component and a second output to provide a phase retarded synchronous signal component, said advanced and retarded reference components having a mutual phase difference of approximately 90*; amplifier means to receive a said modulated input signal, having the output thereof connected to a pair of synchronous demodulators, each said demodulator receiving a respective one of said advanced or retarded reference signal components, the output from each said demodulator being connected with an inverter means, the output from the two inverters together with the output from the two demodulators comprising four outputs having separate signals mutually separated in phase approximately 90*, 180* and 270* selection means connected with said four outputs to identify the one of said signals in accordance with the desired conditioned characteristic, and switching means operated by said selection means to switch said desired conditioned signal to an output amplifier.

Claim 8

Apparatus as claimed in claim 5 wherein said selection means comprises four polarity sensitive selector circuit means, each receiving three of said four separate signal outputs to identify which signal has an instantaneous positive-going value for a selected sense of phase change of said input signal in a phase lagging or a phase leading sense relative to said reference signal, whereby the selected output is substantially insensitive to the variation in the amplitude of said input signal.