Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-01-13
1990-05-15
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
358244, H01J 4014
Patent
active
049260570
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and device for acquiring and integrating repetitive electric signals.
For some years, there has been considerable development in high speed analog or digital oscilloscopes. The signals are stored by transferring to a digital memory in the first case and by means of a photographic system or a video camera in the second.
When a repetitive signal is analysed and when it is affected by random noise, without correlation with the signal, it is advantageous and even necessary to provide the sum or the mean thereof. In fact it is known that the gain of the signal to noise ratio which results from N accumulations of the noise affected signal is equal to .sqroot.N (voltage ratio gain).
This mean is very often provided digitally, either directly by means of processors included in the oscilloscope or by coupling with an external computer, or in a hybrid fashion using a video tape recorder coupled to a system for digitizing the video signal in delayed time.
Each of the above mentioned systems has the main drawback of introducing dead times or limiting the rate of acquiring successive signals:
for digital signals, the transfer time to the storage memory is typically of the order of a microsecond per measuring point,
for video tape recorder acquisition, it is not possible to exceed a rate of a few tens of Hertz.
The document Electronics, vol 49, no. 12, June 1976, pages 113-119 describes either the association with a cathode ray tube or a linear photodiode strip (CCD), or a matrix of such strips, placed upstream of the screen of the tube and receiving the electron beam therefrom, modulated in intensity by the signal.
In the first solution, the electron beam undergoes no vertical deflection, whereas in the second it effects X and Y scanning.
In both cases, the individual detector elements of the strip operate by all or nothing and each strip only delivers a single information (abscissa or ordinate) concerning the signal. The device is not able to follow high speed intensity variations.
It is the same in the CCD strip device described in the document EP-A-0 187 087.
To sum up, none of the above solutions allows repetitive signals with very rapid variation to be recorded in order to find the mean thereof.
The present invention aims at providing a method and device for recording and integrating repetitive signals answering better than those known heretofore the present requirements of signal processing, particularly in that they introduce no limit to the repetition rate of the signals to be acquired and they make it possible to obtain, for a given measurement time, a signal to noise ratio far better than those of systems available on the instrumentation market.
The method of the invention is of the trace analysis type, i.e. it comprises the generation of an electronic beam providing X and Y scanning representative of the amplitude variation of the signal as a function of time (which is not the case in the above document "Electronics").
It is characterized by recording the path of the beam on a strip of detectors each element of which, having the form of a narrow strip of given abscissa and of constant length, receives a flux proportional to the ordinate of the point of the path which corresponds to said abscissa.
Thus, the horizontal coordinate (usually the time) is associated with the position of a detector of the strip, whereas the vertical coordinate (amplitude of the signal to be measured) is proportional to the charge of this detector.
For integrating the signal, the method comprises the accumulation of the charges generated in the strip during a pre-determined number of passages less than that which would saturate the detector elements and reading the strip to collect information of the mean ordinates.
In a preferred embodiment of the device of the invention, each point of the path is transformed by an astigmatic optical system into a light segment of constant length projected with off-set on the corresponding element of the strip so that it covers a light band of height proportional t
REFERENCES:
patent: 2324851 (1943-07-01), Koch
patent: 4305098 (1981-12-01), Mitchell
patent: 4673269 (1987-06-01), Schiff et al.
Electronics, vol. 49, No. 12, 6/1976, New York, Shaphard: "Advances in CRT Design Augur Improved Oscilloscopes", pp. 113-119.
Hewlett-Packard Journal, vol. 33, No. 4, 4/1982, Oldfield et al.: "Wideband, Fast-Writing Oscilloscope Solves Difficult Measurement Problems", pp. 26-31.
Boccara Alberr-Claude
Charbonnier Francois
Fournier Daniele
Drucker William A.
Nelms David C.
Shami Khaled
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