Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Patent
1992-07-24
1993-11-23
Hellner, Mark
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
356 28, G01P 336
Patent
active
052649083
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an optical device for measuring the speed or length of a moved surface, where a measuring light beam from a laser is directed towards the surface and the Doppler-shifted dispersed light reflected from the surface and other light, for example laser light which is not Doppler-shifted or another Doppler-shifted laser light, are overlaid to produce a beat whereof the frequency forms a measure of the speed of the surface and is received and evaluated in an evaluation system in the form of continuously occurring digital signals.
In the development of the evaluation system, the fact that the length information obtained by the measuring process is based on a quantization in the order of magnitude of 10 .mu.m must be taken into account. Because of the speed of the material measured, which may be high, and the frequency offset used, the measured frequencies may be up to 10 MHz. For the measuring process to be accurate, it is necessary for the evaluation system to detect and evaluate all the length increments.
When using the hitherto conventional analog evaluation systems having so-called tracking filters, false measurements are often produced, particularly if the useful signal cannot be clearly separated in the evaluation system from the noise components.
In a further known evaluation system, the measured frequencies are measured in a measuring cycle and evaluated by integration in a subsequent evaluation cycle. It is true that here only an individual rapid counter of low counting capacity and a downstream adding mechanism of low speed are used so that the expenditure for equipment remains on an acceptable scale; however, with this solution it is not possible to count and add at the same time, so that individual length increments are not detected, so that falsifications in the result are caused by the alternating measuring and evaluation cycles.
With a maximum length of measured material of 100 km, evaluation may also be performed by a synchronous 35-bit incremental/decremental counter having a maximum counting frequency of 10 MHz. However, this solution would necessitate a considerable expenditure for hardware.
It is thus the object to provide an evaluation system by means of which the signals, namely the measured frequencies, are received and evaluated continuously without loss of information, without a disproportionately high expenditure being necessary for this.
In accordance with the invention, this object is achieved in that, in an optical device of the type mentioned at the outset, there is downstream of a counter intended for detecting the signals and having a high counting speed an intermediate store which is connected to an adding mechanism for pulse-wise transmission of the counter contents, in that a control mechanism for sequence control is connected to the counter, the intermediate store and the adding mechanism, and in that a pulse generator is upstream of the control mechanism.
The main advantage of this evaluation system according to the invention consists in the fact that it receives and processes the signals occurring continuously from the optical system, that is to say the measured frequency values, continuously, so that thus all the length increments are measured continuously at any speed of measured material and a correspondingly high accuracy of measurement results.
For the simultaneous rapid counting of the signals, a correspondingly rapid counter is provided which can, however, have a low counting capacity and thus requires only a low expenditure by comparison with the prior art.
The signals which have been counted by the counter within a predetermined sampling time ar transferred, once the sampling time has expired, to the store, which passes the signals on to the adding mechanism, where they are added, or subtracted as appropriate, to the previous result. The essential point is that there is available for this transfer and addition a period of time which corresponds at most to the sampling time, that is to say the pulse time. This time is sufficient for this functi
REFERENCES:
patent: 3738750 (1973-06-01), Kalb et al.
patent: 3982101 (1976-09-01), Kalb et al.
patent: 4912519 (1990-04-01), Yoshida et al.
patent: 4925297 (1990-05-01), Brown
Hellner Mark
Mesacon Gesellschaft fur Messtechnik mbH
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