GB2025618A - A system for recording electrical signals - Google Patents

Abstract

A system for recording random electrical signals on a paper tape 46, in which the output paper tape recorder 25 of the system is preceded by a floppy disc magnetic recorder 50, means being provided for activating the paper tape recorder 25 before the receipt of the signals which have been delayed by being memorized in a semiconductor circuit 43. The input signals are only recorded if they vary significantly from a steady state. <IMAGE>

Description

SPECIFICATION A system for recording random electrical signals This invention relates to systems for recording random disturbances of the type which can occur in industrial installations and, more particularly, in electricity supply networks.

In this latter case in particular, the notion of service is fundamental and any incident, such as a variation in the voltage of the electricity, for example an overvoltage or an undervoltage sufficient to bring about a total breakdown in supply, requires that a complete analysis of the phenomenon should be able to be subsequently made in order to determine its causes and to prevent it from recurring. These causes are various and may be related to accidental damage to the supply lines or their associated components (circuit breakers, isoiators); they may emanate from undesirable contacts or from short circuits momentarily affecting certain components of these lines. In the case of overhead lines normally supported by pylons, a frequent cause of disturbances may be attributed to atmospheric electrical discharges, such as those due to lightning.

In any event, the monitoring of these unforeseeable disturbances necessitates on the one hand continuous surveillance and, on the other hand, the possibility of subsequently analysing each phenomenon which in turn necessitates the use of recording means.

Recording means such as these generally use an information support in the form of a moving tape on which the values to be monitored are recorded in the form of visible signals either directly or after a suitable treatment.

In the majority of cases, the material used for the support is paper which lends itself to convenient direct visual examination, to subsequent additional recording and to filing.

The recording is generally made with ink or, less frequently, using a photographic means with, in this case, the possibie need for processing.

However, the continuous recording of the values to be monitored results in an unacceptable consumption of paper, the incidents only occurring infrequently and, as already mentioned, randomly.

In order to reduce the amount of recording support used, it has already been proposed to make the recording only when a disturbance occurs.

This system of operation in the tripping mode is activated by the occurrence of the disturbance itself, the recorder remaining inactive between two disturbances.

However, the exact determination of the causes of the incidents makes it desirable to know not only the disturbed state as a whole but also the stable state prevailing immediately before the incident.

Accordingly, when an incident occurs, the recorder has to begin recording before the arrival of the disturbance signal, a requirement which can only be satisfied by the insertion of an element which introduces a delay between the moment when the signal corresponding to the disturbance activates the recorder and the moment when the recording itself begins.

This element performs a function which will be referred to hereinafter as a pre-activation memory.

In some known paper tape recorders, the preactivation memory is of the mechanical type. It is formed by a rotating intermediate support in the form of a cylinder on which the last few seconds of the value to be monitored are graphically recorded and then permanently erased. The transfer by contact to the paper tape, which is normally stationary, only takes place in the event of an incident. The pre-activation memory is thus represented by the value of the angular displacement between the writing points and contact points between the rotating cylinder and the paper.

In other paper tape recorders, the pre-activation memory is electricallyformed by a digital circuit of the "shift register" type. The analog value to be monitored is converted beforehand into a digital value and, after having been delayed, is converted back into an analog value at the register output for the final recording on papertape.

Given acceptance of the reduced separating power and the lack of precision inherent in recording in real time on paper tape, it has been possible to obtain satisfactory results with disturbance recorders of this type at the cost of attentive surveillance for keeping the recorder adequately supplied with paper tape and the maintenance of an optimal environment adapted to the recording process used.

However, in numerous other practical cases, these requirements cannot be satisfied. This is because, due to their particular characteristics and to the wide band of frequencies which they contain, the electrical disturbance signals, which often appear at extremely remote points of the networks to which access is difficult, cannot be conveyed by conventional electrical lines to an operations centre where the recording apparatus can be conveniently grouped, observed and maintained. Accordingly, one of the limitations of using apparatus of this type lies in the fact that they have to be installed on natural sites often separated by considerable distances to which only very infrequent periodic visits can be made for removing the recorded supports and, if necessary, replacing them by black supports.

This means that, in order to reduce the consumption of paper, it is necessary to select a limited tape speed which in turn results in a low resolving power and complicates analysis of the results which have to be examined under a magnifying glass. In general, the total capacity of the system is limited by the size of the roil of paper.

In addition, in the event of a failure in the operation of the paper tape recorder, no trace of the disturbance to be studied is left which seriously endangers the reliability of surveillance at remote sites.

In order to improve reliability, it has been proposed to replace the process of recording on paper tape by recording on magnetic supports, generally in the form of tape cassettes, either in analog form or in digital form.

However, in view of the orders of magnitude of the data to be recorded, the numerical input and output speed of a cassette remains low, limiting the rate of flow of information per second, particularly when several input channels have to be monitored. In addition, cassettes are fragile, difficult to change at frequent intervals at remote sites and leave no material graphic trace directly visible at remote sites for analysis and additional annotation. This particular disadvantage, although associated with a distinctly higher input rate, may be offset in cases where the magnetic support is formed by a floppy disc.

The present invention relates to a recording system which is not attended by any of these disadvantages, but instead has the combined advantages of the two types of information support, namely the magnetic support in the form of a floppy disc and the paper tape.

According to the invention, the known system of recording on paper tape is completely retained, the basic feature of the invention consisting in the insertion between two links of this system of an additional recording means comprising a magnetic support of the floppy disc type.

The association of a floppy disc with a paper tape thus constitutes a combination co-operating to achieve a common objective, providing on the one hand a high-capacity, high-resolution store facility for a large number of non-directly accessible data and, on the other hand, a direct visual examination means for analysis and action, the common objective achieved being the reliability and precision in the knowledge of the disturbances in question.

In a first mode of operation of the system, the paper tape recorder may remain permanently inactive, being activated only during periodic visits under the surveillance of the visiting official who is thus readily able immediately to see any desired part of the recording of the floppy disc.

The choice and the surveillance of the official firmly guarantees a good recording on paper with an increase in the tape speed to obtain better resolution.

In a second, particularly advantageous mode of operation of the system, the paper recorder need not be permanently installed at the site, but instead may be brought aiong by the visiting official so that a single recorder may serve several widely scattered sites. This mode of operation is permitted by the invention, the means required for extracting, processing and recording on paper the data contained in the floppy disc already being largely present in the fixed part of the system, so that the paper recorder may be lighter in weight and more transportable.

In a third mode of operation of the system, the paper recorder is installed in a central location provided with technical means affording every guarantee of recording quality and the visiting official conveys the floppy disc recorded on the site to a reader for floppy discs installed in the same central location.

In this case, the official is no longer in possession on site of means for permanently displaying the information contained in the floppy disc. However, the weight to be transported, namely the floppy disc, is greatly reduced by comparison with the paper recorder of the second mode of operation. In this case, the invention, which affords the advantage of enabling the secondary recording to be made on paper from a primary recording on a floppy disc, overcomes the limitations inherent in conventional direct recording on paper tape, namely a reduced resolution and/or a high consumption of paper and/or poor reliability. This is because each incident or disturbance may be readily displayed on paper on a large scale and with high resolution and conventional recorders, for example using an ink pen, may be usedforthis purpose.

In one preferred embodiment, however, the invention may advantageously be worked by a particular choice of the paper display recorder using ultraviolet recording on a paper sensitive to ultra-violet radiation created by the moving spot of cathodic oscilloscope. The resulting lightness and simplicity of the paper recorder are particularly advantageous in the case of the second mode of operation described above.

In addition to the recorded analog diagram itself, this system enables all the alpha-numeric identification data considered necessary and present on the magnetic support (place, date, time of recording, etc....) to be recorded.

It should also be pointed out that the insertion of a floppy disc stage, where the recording is normally made in digital form, advantageously lends itself to association with a digital pre-activation memory provided either at the output of this stage or at its input.

In this particular case, a memory such as this enables the floppy disc to be used to particular advantage by also subjecting it to the tripping mode and by leaving it inactive between two disturbances in the same way as the paper tape reacorder.

On the other hand, it is pointed out that the intermediate recording on a floppy disc provides for a significant improvement in the reliability of the system, the floppy disc stage being essentially electronic in design, having a reduced power consumption and comprising only a small number of mechanical elements which, moreover, remain inactive during its monitoring function between two disturbances.

Accordingly, after transfer to the paper tape, there are two documents which provide an additional guarantee in the event of damage or loss.

Finally, it is pointed out that the use of a floppy disc stage as an intermediate link brings to the analysis of the random disturbances all the advantages of recording the data in digital form, in particular the location of disturbances defined by their characteristics, the comparison between recordings of the same disturbance emanating from different monitoring stations, the possibility of using any law of compression for the data adapted to the type of disturbances, etc.

Accordingly, the invention consists in a recording system for displaying random electrical disturbances, comprising on the one hand a plurality of input matching circuits for introducing the signals, a first stage for multiplexing the signal, a second stage for delaying the multiplexed signals, this second stage comprising an input analog-digital conversion circuit, and a third stage which is activated by said introduction for displaying the retarded signals, characterised in that an additional stage, comprising a magnetic recording system of the "floppy disc" type, is inserted between the second and third stages.

tThe invention will be better understood from the following description in conjunction with the accom panying drawings, wherein: Figure 1 illustrates a conventional paper-tape recording system.

Figure 2 shows a recording system according to the invention.

Figure 1 shows a paper-tape recording sytem corresponding to the prior art.

It comprises, on a first channel, an input matching stage 11 for the valuesor electrical signals to be recorded which is formed by a plurality of cells, such as 12, a second multiplexing stage 7 connected to the first stage, a third stage 21 for delaying the signals, a fourth multiplexing stage 17 synchronised with the multiplexing stage 7 by the connection 20 and a fifth and last stage, a paper-tape recorder 25 with a recording input, such as 18, connected to the preceding stage.

The conventional recording system additionally comprises a second channel 30 connected in parallel with the first channel after the multiplexing stage, this second channel being connected to the paper tape recorder by a recording control circuit 32.

Finally, a time-and-date circuit 41 is connected to a recording input 70 of the recorder.

A system such as this operates as follows: The values or electrical signals corresponding to the data to be recorded are applied to the input terminals, such as 1,2,3, of level, pass-band etc. matching circuits such as 4,5,6 12.

At the output of this first stage, the signals are applied to the input terminals, such as 8, 9, 10, of a multiplexing circuit 7. The function of this second stage is successively to scan all the signals by repetitive scrutinisation in order to deliver their values to a single output terminal 13.

The two channels 29 and 30 of the system are connected to this terminal. Through the direct channel 30, the appearance of a signal to be recorded sets the recording support in motion through the control circuit of the recorder 32.

Through the retarded channel 29, the signal under goes in the signal retarding stage 21 a delay in transmission which, after the demultiplexing stage 17 will ensure the required result of applying the signal to the recording input terminal 18 of the recorder only after the recording support has been setinmotion.

The design of the delay stage was governed by the fact that it is easier to delay the propagation of an electrical signal in digital form than in analog form. It is for this reason that, according to the prior art, the retarding stage comprises an analog-digital conver sion circuit 42, a retarding circuit of the type known as a shift register 43 and a digital-analog converter 44.

The disadvantages of a recording system such as this have already been mentioned and arise out of the limited resolution of the paper-tape recordings made in real time. A modification to this system, whereby the signal is momentarily placed in a semiconductor memory and subsequently displayed on paper with a higher resolution, would result in the need for very large dimensions of this memory and/or even in a limitation of the duration of the recordable disturbances.

Figure 2 shows a recording system according to the invention.

In a drawing where the same elements as those in Figure 1 are denoted by the same reference numerals, it is characterised by the insertion in the retarding stage 21 of a magnetic floppy disc recorder.

A system such as this operates as follows. The signals to be recorded, which are applied in analog form to the inputs, such as 1,2,3, and multiplexed at 7, are converted into digital form in the conversion stage 42. For the reasons explained in detail above, they are then retarded in a semiconductor memory circuit 43 and introduced into the floppy disc recording stage 50. This stage comprises the actual recorder 51 and the associated circuits 52 for processing the signals to be recorded and controlling the recording operation itself.

As in the conventional system shown in Figure 1, the signal is applied at the output of the floppy disc recording stage to a digital-analog conversion stage 44, a demultiplexing stage 17 and a paper-tape recording stage 25.

At 53, the associated circuits 52 perform a "timeand-date" function materialised by a real time counter controlled by a synchronisation line leading to an external time-and-date clock 54. In addition, the real time counter supplies the signals for activating the input scans through the line 55. On the other hand, the associated circuits perform at 56 a function whereby the digital signals are treated and, at 57, a function whereby the words are shaped and the identification and date codes inserted. According to one advantageous aspect of the invention, this treatment comprises a programme for compressing the signals to be recorded in dependence upon their significant variations of which the object is not to introduce stationary data into the floppy disc, but oniyto memorize the necessary data in a minimal volume. The data compression programme according to the invention is as follows: On completion of each scanning cycle carried out by the multiplexing stage, the treatment circuit compares the word which has just been memorized on each of the channels with the word memorized on the corresponding channels during a preceding scanning cycle and, depending on the differences observed, the circuit decides whether or not to precede with the recording of the new scrutinisation.

- The decision is made for all the input channels in dependence upon the variations of all the channels: the recording is only omitted if all the channels have remained very close to the value taken as reference.

- In the interests of safety, the treatment circuit limits the number of scrutinisations eliminated to a predetermined value.

- Each scrutinisation recorded is preceded by a code which indicates the number of scrutinisations which have been eliminated since the last recording.

- The scrutinisation taken as reference for the comparison at the instant t may be the scrutinisation made at the instant (t-1), if the quiescent state of the lines under surveillance is totally unknown, or the scrutinisation made at the instant (t-T) if a periodic signal of known period T is normally present on the lines.

The tolerances of the comparison and the limiting value of the number of scrutinisations eliminated are defined in dependence upon the use of the recording system itself.

As explained above, the data may readily be displayed by using a digital-analog converter 44 followed by a demultiplexer 17 synchronised with the multiplexer 42 by the line 45 and connected to a paper-tape recorder 25.

In addition, if the paper-tape recorder is adapted for recording data in digital form, the insertion according to the invention of a digital floppy disc recorder affords the additional advantage that, in addition to the analog data corresponding to the signals, data characterising the date, technical conditions, etc. may be directly added to the paper tape in alpha-numeric form according to any desired character code. This possibility is permitted in particular by cathode tube recorders using paper sensitive to ultra-violet radiation.

For a collection of orders of magnitude given by way of example, the following results were obtained according to whether the disturbance recording system corresponds to the prior art or to the invention: For a typical speed of the paper tape of 20 cm per second, a standard roll of paper 30 metres long used in the conventional system enables disturbances having a maximum total duration of 150 seconds to be recorded with a given degree of resolution. With the insertion of a floppy disc stage according to the invention, the maximum total duration is increased to 400 seconds without compression of the data and to 700 seconds with compression.

Finally, by slowing down the floppy disc during the recording on paper, the expansion of the time scale on the paper enables the degree of resolution to be increased by between 5 and 6 times whilst, at the same time, keeping the consumption of paper at a low level by selecting only those disturbances considered to be of interest.

Claims (10)

1. A system for recording random electrical signals displayed on a moving support (46), comprising a plurality of input matching circuits (4) for the introduction of the signals, a first stage (42) for multiplexing these signals, a second stage (30) for retarding the multiplexed signals, this second stage comprising an imput analog-digital conversion circuit (43), and a third stage (25) which is brought into operation by said introduction, for displaying the retarded signals, wherein an additional stage (52), comprising a magnetic recording system of the detachable "floppy disc" type (51), is inserted between the second and third stages, the disc being immobile between two said introductions.

2. A system for recording electrical signals as claimed in Claim 1, wherein the magnetic recording system comprises a circuit for treating the signals according to a data compression programme.

3. A system for recording electrical signals as claimed in Claim 1, wherein is comprised a demultiplexing stage at the input terminals of the output display stage.

4. A system for recording electrical signals as claimed in Claim 2, wherein the control circuit of the magnetic recording system is governed by the circuit for treating the signals.

5. A system for recording electrical signals as claimed in Claim 1,wherein at least some of the electrical input signals are in digital form.

6. A system for recording electrical signals as claimed in Claim 1,wherein the moving display support is a paper tape, the display being obtained by the action of ultra-violet radiation on a material deposited on said moving support.

7. A system for recording electrical signals as claimed in Claim 1, wherein the output display stage comprises input recording terminals for applying digital signals.

8. A system for recording electrical signals as claimed in Claim 8, wherein said digital signals represent in particular alphanumeric time-and-date symbols.

9. A system for recording electrical signals as claimed in Claim 1, wherein the output display stage is a detachable and portable unit.

10. A system for recording electrical signals substantially as described with reference to Figure 2 of the accompanying drawings.