A METHOD AND A DEVICE FOR RECORDING A DEVIATION OF A MONITORED SIGNAL

Abstract: A method and a device for discovering and recording signal deviations that occur at long time intervals. The method comprises the steps of sensing the signal and analyzing the signal with respect to its frequency content and amplitude, monitoring the signal during a chosen initiation period in which the signal does not contain a deviation that is to be discovered and registered, forming a mean value of the signal during the initiation period and establishing an upper and a lower limit value of the signal, and sensing the signal after said initiation period and comparing the signal with said limit values and recording the signal over a pre-selected time period when one of said limit values is transgressed. The inventive device is implemented with a plug-in board in a personal computer, wherewith the board carried components are designed to carry out the method steps, such that the signal will be recorded on the hard disk of the computer in the event of a malfunction.

Description: A METHOD AND A DEVICE FOR RECORDING A DEVIATION OF A MONITORED SIGNAL The present invention relates to a method of detecting and recording signal deviations that occur at relatively long time intervals, in accordance with the preamble of Claim 1. The invention also relates to a corresponding device according to the preamble of the independent apparatus Claim. The invention finds use in, for instance, identifying a malfunction in an electronic circuit or electronic apparatus when the malfunction occurs with short duration and with long time intervals, and particularly also with a relatively small deviation from a normal function. This type of error is naturally very difficult to locate with conventional methods (cooling and/or heating certain components while simultaneously analyzing resultant signal changes, in order to find malfunctioning components) . Accordingly, an object of the present invention is to provide a technique that will enable the indication of a signal deviation which is indicative of some form of malfunction, and therewith also to obtain information relating to the character of the deviation when the signal deviation occurs over long time intervals, of short duration and of small size. The object of the invention also includes the provision of a technique which can be implemented at relatively low costs, both with respect to apparatus and operator working time. This object is achieved with the method defined in the accompanying independent method Claim. The object is also achieved with the device defined in the independent apparatus Claim. Further developments of the invention will be evident from the accompanying dependent Claims. The signal is initially analyzed with respect to its frequency content and amplitude and a mean signal-value is thereafter determined on the basis of the frequency analysis. An upper and a lower limit value of the formed mean-value signal is also determined. The measured object must behave faultlessly during this initiation phase and may not exhibit any of the faults that have occasioned observation of the signal. In practice, this means that the signal is monitored by an operator during the initiation phase. Because the degree of mean value formation and the upper and lower signal limit values can be established, those occasions on which the signal formed by the mean value exceeds the upper or lower limit value, i.e. shows a deviation or fault, can be detected with the aid of simple means. The mean value of the signal to be monitored is suitably sampled continuously. The transgression of a limit value is utilized to trigger recording of the signal with high information density over a limited time period. The mean value is formed conveniently by quadration, so as to enable any drawbacks or inconveniences with direct mean values for essentially periodic signals to be avoided. The invention can be applied to a signal which, in the absence of malfunctioning, can be mean-value formed with a certain time constant to a constant signal which has a not negligible deviation from a constant signal which with the same time constant is mean-value formed by the signal containing the fault deviations. The invention preferably includes the construction of a plug- in board that can be fitted in a conventional personal computer or the like. The board will include means for forming the mean values of the sensed signal and the value for activating registration of the signal when a limit value is exceeded. The board or card, is suitably constructed for adaptation to different amplitude ranges of the sensed signal and also different frequency ranges of said signal, said board suitably being set to the correct ranges on the basis of the initial signal analysis. When the board triggers registration of the signal, this is suitably registered on the computer hard disk. According to one preferred embodiment of the invention, the signal can also be registered during short time periods at relatively long time intervals, so that slow tendencies towards signal changes can be subsequently followed. When applying the invention, particularly in conjunction with electronic circuits, it is suitable also to sense at least one further signal, so as to obtain comparison material in a subsequent closer analysis of the "erroneous" signal. For instance, the further signal may be registered on the same occasion as registering the primary sensed signal of interest. Alternatively, several different signal can be sensed and registered simultaneously in the same way. According to the invention, a computer can be used for signal monitoring purposes. For instance, after the initiation phase, the computer can be used to log the measurement values at a relatively slow rate until one of the signals transgresses one of its limit values, this transgression causing logging of the signals to commence at a higher rate over a limited time period. One of the advantages afforded by the invention is that a signal can be followed over a long period of time even in the case of a personal computer with its relatively limited memory size, and the course of this signal recorded in conjunction with malfunctioning that occurs at a low frequency. When this measuring process is terminated, the entire measuring sequence can be analyzed graphically on some form of display screen. It is therewith possible to zoom-in graphically on each time point at which a limit value has been transgressed, and the course of the signal compared with that of another signal logged at the same time. This enables the operator to establish the reason for the fault, or at least to come closer to cause of the fault. If the measuring sequence performed does not clearly lead to an indication of the reason for the fault in an electronic circuit, the operator is able to choose a set of other signals on the basis of the result of the first measuring sequence, this second measuring sequence giving a more positive indication of the cause of the fault, or at least eliminating possible fault sources. The invention is, of course, not restricted to use in conjunction with electronic circuits, but can also be used for checking sequences statistically, for instance. the invention can thus be applied in conjunction with manufacturing processes, i.e. statistical process controls of manufacturing processes, with the intention of discovering problems and enhancing the quality of the manufacturing process . The invention will now be described in more detail with reference to the accompanying drawings. Fig. 1 is a block schematic which illustrates the invention. Shown in Fig. 1 is an electronic circuit 1 and a personal computer 2. A signal is taken out from a selected point in the circuit 1 and fed into the computer. The computer is then caused to form a mean value of the signal in a mean-value forming device 21, preferably in the form of a card (a plug- in board) . Initial frequency analysis is used to determine the degree to which the mean-value of the signal is formed. An operator is able to study the signal concerned on a screen 3 that can be coupled to the computer 2. The computer 2 also includes devices 22 for establishing an upper and a lower limit value for the monitored signal forming said mean value. These devices 22 may suitably be included in the insert card. The limit values are established over an initiation period in which the signal must be error-free, or faultless, i.e. exhibit none of the malfunctions that have occasioned the study of the signal. The mean value of the signal to be monitored may be sampled continuously. A triggering means 23 (which is also suitably integrated in the board) is designed to cause the signal to be registered, or recorded, in a recording device 25 (the computer hard disk) over a selected time period, when the mean-value signal has transgressed the upper or the lower limit value of the formed mean value. The signal can be recorded in the recording device 25 with the aid of time controlled elements 24 (which are also suitably integrated in the card) which pass the signal to the recording device 25 during selected time periods at a relatively slow rate. The recording device 25 may comprise the storage means of a personal computer. Naturally, the signal taken from the circuit 1 may also be amplified and processed by the computer 2 or the plug-in board to enable the signal to be shown rapidly on a display device or screen. The recording device 25 is, of course, also adapted to image its recorded contents on the display device, optionally at a different rate. Example of use It is assumed that an audio amplifier that comprises five amplifier stages "produces poor sound" for some minutes in the week. Service technicians are unable to bring forwards the fault with the aid of conventional cooling/heating/ bending techniques and find no way of analyzing the fault. This instrument can now be connected after the last and before the first amplifier stage for instance, and a suitable input signal in the form of a signal generator or noise generator then applied to the amplifier input. The alarm level, frequency range and voltage range of the instrument are then set and the measuring process commenced by monitoring over a period of less than one minute during the time the reference values are set. Monitoring can then be continued for the time necessary to develop the fault. Since the instrument is alarmed, the result is analyzed and a comparison made between the results from the third and the last amplifier stages carried out. If the signal sensed upstream of the third stage is faultless, the sensing point is moved closer to the fault and a new measuring process begun, whereafter the fault is encircled in a resource-lean manner . The inventive device is constructed for rapid results, i.e. to produce a particularly high time resolution of recorded signals. This can be achieved in particular by at least duplicating all important components and parts of the device, such as to establish two or more parallel working channels for parallel sensing of the signals concerned. This endeavour is in contrast to devices of conventional construction with which multiplexing is used. By generating a particularly high time resolution with respect to the recorded signal or signals in accordance with the invention, favourable advantages are achieved when monitoring slow systems or feed-back systems. The order in which the faults occur is then known and the primary fault can then be deduced and distinguished, or separated, from developed signal deviations. It would be difficult to read the primary cause of the malfunctioning in the absence of such high time resolution of the recorded signal.

Claims: CLAIMS 1. A method of discovering and recording signal deviations that occur at long time intervals, characterized by monitoring the signal over a chosen initiation period in which the signal does not contain a deviation that is to be discovered and recorded, and sensing the signal with respect to its frequency content and amplitude, and determining on the basis of the sensed frequency content the mean-value forming degree of the signal, and establishing an upper and a lower limit value for the formed mean-value signal, and at the end of the initiation period sensing the formed mean- value signal and comparing this signal with the mean-value formed limit values, and recording the signal over a pre- selected time period when said signal transgresses one of said limit values. 2. A method according to Claim 1, characterized by recording the signal over short time periods and relatively long time intervals subsequent to said initiation period. 3. A method according to Claim 1 or 2, characterized by logging with the aid of a computer the measurement values relating to the monitored signal at a relatively slow rate until the signal transgresses one of its limit values, wherewith logging is carried out at a higher rate over a limited period of time. 4. A method according to any one of Claims 1-3, characterized by analyzing the measuring sequence graphically upon termination of the measuring process, wherewith an operator studies the measuring process graphically in detail at that time point at which a limit value has been transgressed. 5. A method according to any one of Claims 1-4, characterized by sensing at least one further signal at the same time of sensing the signal of primary interest, and recording said further signal simultaneously with the signal of primary interest. 6. A device for discovering and recording signal deviations that occur at long time intervals, characterized by means for monitoring the signal over a pre-selected initiating period to ensure that the monitored signal does not contain over the initiation period a signal deviation that it is desired to discover and record; means for sensing the frequency content and amplitude of the signal; means for determining on the basis of the sensed frequency content the mean value forming degree of the signal; means for establishing an upper and a lower limit value of the formed mean-value signal; means for sensing the formed mean-value signal subsequent to said initiation period; means for comparing the formed mean-value signal with said limit values; and means for recording the signal over a pre-selected time period upon transgression of a limit value. 7. A device according to Claim 6, characterized by means for recording the signal over a short time period at relatively long time intervals also in the absence of a limit value transgression. 8. A device according to one of Claims 6 or 7, characterized by means for recording the monitored signal with high information density over a limited time period subsequent to the transgression of a limit value. 9. A device according to any one of Claims 6-8, characterized in that at least one further signal is sensed and recorded simultaneously with the signal of primary interest . 10. A device according to any one of Claims 6-9, characterized in that the device includes a personal computer whose memory store forms said recording means and a computer plug-in board or board which contains the remainder of said means .

Inventors: NORDSTROEM CHRISTER, NORDSTROEM, CHRISTER
Applicants: NORDSTROEM CHRISTER, NORDSTROEM, CHRISTER
Application year: 1997
Main classification: G01D1
IPC codes: G01D1