DE3612234A1 - Method and arrangement for data acquisition and data reduction in disturbance value detection systems - Google Patents

Abstract

In the case of a method for data acquisition and data reduction for determining disturbance values in the electricity supply field, the disturbance signals are sampled, digitised and evaluated. In order to make possible a favourable buffer-storage capability for even high-frequency disturbance signals, the zero crossings of the disturbance signal are determined, using comparators, after single and double differentiation and the levels and times of the zero crossings are stored, it being possible to carry out simple reconstruction of the signal behaviour in accordance with conventional algorithms. The invention can primarily be used in electricity supply company monitoring systems. <IMAGE>

Description

The invention relates to a method and an order according to the preamble of claim 1.

In the invention of interference in the area of over monitoring of phase currents and voltages, for example in the field of electricity supply, the over monitored signals are recorded, digitized, into a memory filed and evaluated at a later date. There sufficient with high-frequency components of the interference signals to be accurately detected, it is necessary to use the signals a high temporal resolution.

The acquisition, digitization and storage of the sturgeon data takes place at predefined times. Conditionally through the existing processing and storage medium, a compromise must be made. The sturgeon signals are recorded with a relatively low sampling rate sums up. A microprocessor evaluates these signals and takes a data reduction by means of complicated and time-consuming algorithms. The disadvantage of this ver driving is that timely processing only then is possible if the sampling rate remains low or that timely acquisition and data reduction at high sampling rate, as it would be required, not possible is.

The invention is based, to evaluate the task tendency data in such a way that they on a usual Chen data storage or that these signals over Long-distance lines can be transmitted.

This object is achieved with a fiction according to the method of the type mentioned at the outset Characteristic of claim 1.

Advantageously, it is thus possible to switch off evaluation of the monitored signals using an analog Circuit to specify the time of a scan. The main sizes of interest in the evaluation are maxima and minima of the signal. By differences Decoration of the measurement signal and evaluation of the zero crossings of the differentiated signal, the time of a Ma xima and minima of the measurement signal are determined and thus the Digitization can be triggered. So that the later recon structure of the signal is possible, the time must also these maxima and minima can be determined. This informa tion is obtained from a time counter. Because the monitor ten signals interference in the course of the signal between Wed. nima and maxima must be determined when such an event occurs. Through the difference tion of the previously differentiated signal the turning points are determined and thus the record level and time can be triggered. So that is the reconstruction of the original signal curve with sufficient accuracy in most cases ensures.

With increased accuracy requirements, Ge Generation of the third derivative of the input signal (white further differentiators) and evaluation of the zero crossings rapid changes in the steepness of the input signal be recognized.  

In addition to the triggering of the digitali specified above is a trigger by an overflow of time counter, which is only the time between two Scans, provided. This allows DC voltage conditions or slow changes in the monitored signal be recognized. Furthermore, since only time spans he can be grasped, the required size of the time memory The data word provided remains limited.

A modification of this procedure can be found in the recording and playback of musical information with CD (Compact Disc) and a better one Enable playback. By evaluating the minima and Maxima of the input signal and coding of the time information tion in the LSB (Last Significant Bit) can in the signal curve the high-frequency portion can be reproduced better.

The method according to the invention can be particularly advantageous with an arrangement specified in claim 2 leads.

The invention is described in more detail with reference to two figures ben and explained, being

Fig. 1 is a block diagram of an embodiment for performing the data acquisition and reduction in a fault detection system and

Fig. 2 shows a waveform at a fault value.

In FIG. 1, a low-pass filter TP is shown, the transition from the one to a sample and hold SH and to a differentiator block D 1 is performed. The output of the differentiator is on the one hand to a further differentiator D 2 and to a zero crossing detection circuit NE . Both the output of the differentiation RERS D 2 and the first zero-cross detection TIC NE 1 as well as the output of a further, renzierer the Diffe D circuit 2 downstream zero-crossing detection NE 2 is the input of a control TIC ST performed. The output of the sample-and-hold circuit SH is led to the input of an analog / digital converter AD , the sample-and-hold circuit being clocked from the output of the control ST ; this clock is also present at the input of the analog / digital converter AD like a time counter Z. The overflow output of the time counter Z is switched to a third input of the control ST . The output signals are the level, the time value and the control clock T.

In the case of the signal curve S shown in FIG. 2, the actual signal is shown in dotted lines. The highlighted points represent stored values of this signal according to amplitude and time. In the example shown, the signal is reproduced with a resolution of 455 μs and a frequency of the basic signal of 50 Hz. Part of this signal profile S 1 is detailed with a different resolution of 110 µs shown at the same basic frequency.

The function of the exemplary embodiment of the fault detection system is explained below. Quick yourself changing signals are processed so that they can be processed can be periodically with a signal, the Fre quenz is higher by a certain factor - after the Shannon's theorem more than twice - sampled. This The process corresponds to a modulation of the scanning Si gnals, which is also a by-product of an amplitude module tion of the demodulated measurement signal caused.

The amplitude modulation of the measurement signal can be very easily calculate according to the following formula:  

Fa = sampling frequency, Fs = frequency of the measurement signal, AM % = amplitude modulation of the measurement signal.

It should be noted here that individual signal peaks too subject to the above effect.

So that the amplitude of the measurement signal with an accuracy of 0.1% is detected in each period, the sample must frequency seventy times higher than the frequency of the measurement signal lie. 1% accuracy means less scanning frequency (22 × frequency of the measurement signal).

The signals that are captured, digitized and further processed works or just saved (e.g. musical Signals or interference signals), are random and exist at least from individual impulses. So that capturing this Signals can be made with the desired accuracy, it must be ensured that the sampling frequency is off is chosen high enough. This means that quick, expensive sample-and-hold and analog / digital converters be used and that a digital, timely Next processing of the signals with standard processors not is possible.

Optimal data acquisition should be such that the ver worked signals are as pure as possible. If instead of specifying the measured value too firmly only the time of relevant changes tion of the measurement signal and associated level recorded a much higher sampling rate is proposed deceives. An automatic adjustment of the number of meas value at the frequency of the monitored signal is through given such a procedure.

When recording fault values in the field of electricity supply voltages and currents must be monitored,  whose fundamental frequency is 50 or 60 Hz and whose Frequency spectrum ranges up to approx. 550 or 660 Hz. These Signals are predominantly periodic in nature (phase span voltage / current). Aperiodic signals (during switching operations) and unique peaks also occur. All these Sizes must be recorded so that a well-founded Ana lysis and an unadulterated graphic output into one can be done later.

For this to happen, conventional systems must the time resolution and thus the sampling rate correspond appropriate maximum frequency and desired accuracy be placed. Signals with a frequency of 660 Hz and a level resolution of + ¹ / ₁₂₈ must be conventional with with a temporal resolution of 60 µs (16 500 Hz) be steady. This means a very high data rate not justifiable with the means available is.

The simple shown in the embodiment analog preprocessing it is possible to make the striking Determine points of the monitored signals. It can be easily verified that maximum, minimum and Turning points of a curve are sufficient to complete this curve reconstruct.

The analog preprocessing must accordingly enable the acquisition of these points. By means of the two differentiators D 1 , D 2 and two comparators (zero crossing detection circuits NE 1 , NE 2 ) connected in series, which determine a change in the polarity at the output of both dif ferentators D 1 , D 2 , the digitization of the current level can be controlled and the point in time or the time span between two sampling points of the signal curve S or S 1 according to FIG. 2 can be determined.

Through this simple process is a first data reduction reached (8 bytes per period of a sine vibration). A huge relief for the microprocess this gives sors. Thus, one more data reduction by means of the known methods relatively time done uncritically.

The reconstruction of the input signal can be done using a programs with the help of e.g. B. Lagrangian Polynomials or the cubic spline function (see e.g. Micro-Computer 12/85, Franzis-Verlag, Sei 108 and 109).

Claims (3)

1. Method for data acquisition and reduction in the determination of interference in monitoring systems for phase currents and voltages, in which

• - the interference signals (S, S 1 ) are sampled, digitized and evaluated,

characterized,

• - That after two differentiations of the signal Minima and maxima of the interference signal are determined and the Scanning and digitization are triggered and
• - a simple reconstruction after buffering and evaluation of the signal curve is carried out.

2. Arrangement for performing the method according to claim 1,

• - With two series-connected differentiators (D 1 , D 2 ), at the outputs of which there is a zero-crossing detection circuit (NE 1 , NE 2 ), the signal to be evaluated via a low-pass filter (TP) at the input of the first differentiator (D 1 ) ( S) is present,
• - with a control (ST) , at whose input the outputs of the zero crossing detection circuits (NE 1 and NE 2 ) are present and the overflow output of a time counter (Z) ,
• - With a sample-and-hold circuit (SH) , at whose input the output signal of the low-pass filter (TP) is present and whose output signal is routed to an analog / digital converter (AD) , the clock inputs of which are clocked by the output of the control are and
• - With outputs for the level value on the analog / digital converter (AD) and the time value on the time counter (Z) .