Jenoptik Aktiengesellschaft

Jenoptik Gmbh

Ehrhard Dammann

Juergen Bauer

Processes and arrangements for the evaluation of laser Doppler signals, especially in laser Doppler anemometers (LDA) or vibrometers, are disclosed. The object of these processes and arrangements is to find a simple possibility for evaluating laser Doppler signals which retains the advantages of conventional frequency tracking demodulation and permits dependable actual measurements of velocities and derived movement values also for extremely low velocities and discontinuous particle flows. This object is achieved with the use of a laser Doppler anemometer (LDA) with bandpass filtration and frequency tracking demodulation, by generating at least one orthogonal frequency system which, as a sequence of four state intervals in an invertible one-to-one correlation, is formed of two additively superimposed rectangular functions with a phase displacement of .pi./2, a detector signal containing the Doppler frequency (f.sub.D) is compared after bandpass filtering with respect to its phase with the state intervals of the orthogonal frequency system, wherein a change in the phase position relative to the orthogonal frequency system triggers a compensation of the change in Doppler frequency generating a regulated mixing frequency (f.sub.M) which is coupled into the LDA, and the regulated mixing frequency (f.sub.M), as an equivalent of the Doppler frequency (f.sub.D), is likewise compared with an orthogonal frequency system and, as a result of the one-to-one sequence of state intervals, is evaluated such that the direction is designated.

Process and arrangement for the evaluation of laser doppler signals

A process is provided for measuring physical values of light-scattering moving particles by means of laser Doppler anemometry and to a corresponding laser Doppler anemometer (LDA) with phase modulation. Generating a moving intensity-modulated superimposition signal in the measured volume of a LDA which is based on an uncomplicated driving of the phase modulator is achieved by having the phase modulator being driven by two sinusoidal driving signals with different frequencies (.omega..sub.1, .omega..sub.2) which are coupled so as to be fixed with respect to phase and frequency and wherein one frequency (.omega..sub.2) is an integer multiple of the other frequency (.omega..sub.1), and a filter frequency (f.sub.F) which is a common multiple of the two frequencies (.omega..sub.1, .omega..sub.2) is filtered out from the output signal of the receiver by a bandpass filter. For this purpose, one of two sidebands occurring in the output signal of the receiver is suppressed by the appropriate amplitude adjustment of the driving signals at the phase modulator. The process and related arrangement are used for measuring velocity in flowing media and for measurements of length and acceleration of solid surfaces.

Process and arrangement for the measurement of physical values of light

A phase-modulated interferometer has improved control and signal processing. Superimposition signals capable of evaluation in a phase-modulated interferometer without a complicated sawtooth control of the phase modulator are attained, in that two sinusoidal control signals which have modulation frequencies (.omega..sub.1, .omega..sub.2) and are rigidly coupled with respect to phase and frequency are applied to the known phase modulator and a cosine signal which is used in a conventional manner for evaluating the phase displacement is filtered of the superimposition signal generated in the interferometer by an electronic bandpass filter. At the filter frequency (.omega..sub.F) of the bandpass filter, an odd-number harmonic and an even-number harmonic of the two modulation frequencies (.omega..sub.1, .omega..sub.2) have the same frequency, when the amplitudes (.phi..sub.1, .phi..sub.2) of the control signals satisfy the condition for the suitable operating point of the phase modulator. The improvement has application to phase-modulated interferometers, in particular, for precision distance measuring devices, preferably by the heterodyne evaluating method.

Multiple control frequency phase modulator in phase modulated

A phase-modulated interferometer with novel control and signal processing utilizes superimposition signals capable of evaluation in a phase-modulated interferometer without complicated control of the phase modulator. A sinusoidal control signal with a modulation frequency (.omega..sub.0) having an amplitude (.psi..sub.0) is supplied to a known phase modulator. Multiplicative mixing of the superimposition signal produced in the interferometer from the measuring and reference arm with a sinusoidal signal of a determined mixing frequency (.omega..sub.M) which is rigidly coupled with respect to phase and frequency with the control signal is effected. When the amplitude (.psi..sub.0) of the control signal satisfies the condition for a suitable operating point of the phase modulator, a cosine signal conventionally used for evaluating the phase displacement is filtered out in an electronic bandpass filter at whose filter frequency (.omega..sub.F) the sum and difference frequencies of two harmonics of the modulation frequency (.omega..sub.0) and the mixing frequency (.omega..sub.M) assume the same value. The invention is applied in phase-modulated interferometers, in particular for precision distance measuring devices, preferably by the heterodyne evaluating method.

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Jena, Germany

Ehrhard Dammann