Abstract: An electrical circuit has, for measuring the frequency of laser Doppler signals, at least one counter for counting the signal pulses and a microprocessor for evaluating the counter reading which is produced within a measuring interval. A high degree of accuracy in the frequency measurement of laser Doppler signals is achieved, in that for controlling the pulse count a blocking element, such as an And-gate (2), which is controlled by means of an additional signal, for example by an automatic band pass, is connected in series with the laser signal pulse counter (4), and also in that there is arranged a time pulse counter (7) which is connected for example to a quartz pulse generator (8) and determines the measuring interval by means of a predetermined number of pulses, and finally in that the laser signal pulse counter (4) and the time pulse counter (7) are connected to a microprocessor (14) for reading the counter readings on completion of a measuring interval.

Abstract: The invention relates to an optical device which serves in particular for measuring the speed of a moved surface with the aid of a measuring beam from a laser. The measuring beam is split into two parts, directed through prisms to converge towards the moved surface and received again frequency-shifted by the Doppler effect. For each part beam there is a single prism body through which each part beam is guided outwards to intensify splitting and is deflected to bring about convergence. Each prism is preferably secured to a plane-parallel glass plate so that very good, lasting adjustment is possible.

Abstract: The invention is directed to an optical instrument comprising a housing and at least one optical assembly enclosed by said housing and mounted on a stage plate. The stage plate is supported on the base plate with the aid of supporting means which guarantees on the one hand a precise fixing of the stage plate compared to the base plate and thus the housing, and on the other hand allows the base plate to distort by whatever attacks without a transfer to the stage plate. There are three supporting structures of different kinds which fix three different points in a special way. Upon the disconnection of the third supporting structure the stage plate can be lifted like a lid around an axis which is the middle axis of the first and second supporting structure.

Abstract: The invention concerns a signal frequency processing device for measuring the frequency of an input signal, wherein the frequency is so much processed that it can be used for producing a TTL-compatible signal. The input signal is mixed with the frequency of a frequency generator and filtered by a band pass filter having a predetermined centre frequency. The resulting signal is mixed again with the oscillator signal of the frequency generator to provide a second intermediate signal. When this second intermediate signal has been passed through a second band pass filter an output signal is obtained which directly corresponds to the input frequency. Unlike in prior art, the control voltage of the frequency generator is not measured and evaluated as an output quantity, but instead the second intermediate frequency obtained in the second mixer.