Title: Method and device for recording, in real time, non uniformly variable data with compression of data during periods of relatively slow variation thereof

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Abstract: The data is stored in the digital mode. The device comprises a sampler and converter from the analogue to the digital mode, a first set or cascade of shift registers for data, a computing and comparison unit with switching means, a second set or cascade of shift registers for the time intervals, addition units adding one digit (+ 1), subtraction units, a logical unit with control units, and a memory or storing unit. The device may be used in a high voltage station for monitoring an electrical network to detect possible faults. The object of this invention, is to provide a method and a device for recording, in real time, non uniformly varying data with compression of data during periods of relatively slow variation thereof. Already known are data recording methods and devices which store, in digital form, data representing a variable phenomenon, the variation of which is produced at variable frequency, for example when it is a matter of both a permanent process (or operation) and a transient process (or operation). In this case, it is necessary, if it is wished to avoid making use of a very big storage capacity, to proceed with the compression of data during periods when the phenomenon under study varies slowly with respect to time. For example, the "fan" method is known. In this method, the frequency with which the sampled data is stored, follows a very complex law, which makes it difficult to code the instants of sampling, at the same time involving material errors between the compressed signal which is stored, and the original signal which corresponds to the phenomenon under study. It was also suggested to carry out the recording at a slow rate for the permanent process and at a very high rate for the transient process, but problems arose concerning the transfer from one rate to the other and the synchronization between the recording and the phenomenon. The storing of data on a magnetic record in analog form was also used but such a method requires a very wide pass band, and therefore, in the corresponding device, a very high tape speed of the magnetic recording carrier (tape or disk) relatively to the magnetic recorder heads which limits the duration of the phenomenon being stored unless very cumbersome mechanisms and carriers are used. Such a magnetic record also needs high precision rotary devices to be used and generally has to be operated in a controlled environment. The object of this invention is to provide a method and a device which allows an efficient compression, and therefore a smaller storage capacity for the recording of a relatively long phenomenon, with a small error between the reproduced signal from the recording and the original signal produced by the phenomenon under study. The method, according to the invention, for recording, in real time, non uniformly variable data, with the compression of data during periods of relatively slow variation thereof, is characterized by the fact that it comprises in combination, ON THE ONE HAND, THE FOLLOWING SUCCESSIVE OPERATIONS: CONSTANT RATE SAMPLING OF DATA IN DIGITAL FORM; STORING THE SAMPLED DATA IN THE FORM OF A SERIES WITH A DETERMINED NUMBER OF SUCCESSIVE SAMPLED DATA; STUDYING, DURING NORMAL FUNCTIONING OF A SET OF THREE SUCCESSIVE DATA STORED FROM THAT SERIES TO CHECK IF THE DIFFERENCE BETWEEN THE CENTRE DATA OF THIS SET OF THREE AND THE ARITHMETIC MEAN OF THE TWO EXTREME DATA THEREOF IS SUPERIOR OR INFERIOR, IN ABSOLUTE VALUE, TO A GIVEN LIMIT; PERFORMING IN RESPONSE TO SAID CHECKING, OF ONE OR THE OTHER OF THESE TWO OPERATIONS: THE FIRST, WHICH IS CARRIED OUT IF THE AFORESAID DIFFERENCE IS INFERIOR, IN ABSOLUTE VALUE, TO THE SAID LIMIT, CONSISTS IN SUPPRESSING THE CENTRE DATA OF THE SET OF THREE AND TO INCREMENT BY ONE ROW IN THE SERIES ALL THE DATA WHICH COME AFTER THE SUPPRESSED MIDDLE DATA, THE SECOND, WHICH IS CARRIED OUT IF THE DIFFERENCE IS SUPERIOR, IN ABSOLUTE VALUE, TO SAID LIMIT, CONSISTS IN MEMORIZING THE OLDEST DATA OF THE SERIES BY INCREMENTING BY ONE ROW ALL THE STORED DATA OF THE SERIES OF DATA; STORING A SAMPLED DATA IN THE MOST RECENT ROW OF STORAGE WHICH HAS JUST BEEN VACATED BY THE FORWARD MOVEMENT OF PART OR ALL OF THE DATA ALREADY STORED; AND ON THE OTHER HAND, IN PARALLEL WITH THE PRECEDING OPERATIONS OF STORING, STUDYING FORWARD MOVEMENT AND MEMORIZING OF SUCCESSIVE DATA, THE SUCCESSIVE OPERATIONS OF STORING AND MEMORIZING THE TIME INTERVALS SEPARATING THE EFFECTIVELY STORED, AND THEN MOMORIZED DATA. A device, also according to the invention, for embodying said method comprises, in combination: a constant rate sampler for data in digital form; a first cascade set of shift registers, the input of the first register of this stage being connected to the output of the sampler, for the storing of sampled data; a calculator and comparator unit, with three data inputs, designed to differentiate between the signal on its second input and the arithmetic mean of the signals on the first and third inputs and to compare the absolute value of this difference with a limit value applied in the form of a signal on a fourth input; switching means, the inputs of which are connected to the outputs of the shift registers of the first set and which is designed to switch to their three outputs, which are connected to the three inputs of the comparator unit, three consecutive outputs chosen from among the outputs of the aforesaid registers; a second cascade set of shift registers, the number of which is equal to the number of registers of the first set less one unit, for recording the time intervals between data stored in the registers of the first set; adder units to add one unit to the signal applied on its input, connected between the successive registers of the second set of registers as well as being upstream the first register of this set; subtracter units to subtract the value of the input of the adder unit preceding it from the value of the output of the registers of the second state; a logic unit, the inputs of which are connected to the outputs of the aforesaid subtractor units and which determines the three successive registers of the first stage the outputs of which will be connected through said switching means to the calculator and comparator unit; a control unit transmitting the decisions of the logic unit to the switching means to the registers of the first and second sets and to the adder units; and a storing or memory unit with one part, the input of which is connected to the output of the last register of the first set, and a second part, the input of which is connected to the output of the last register of the second set.


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