EP0141929A1 - Method and arrangement for measuring modifications of the capacitive state at a protecting fence - Google Patents

Abstract

At a security fence comprising a plurality of electrodes disposed in parallel, a transmitter applies an alternating voltage to at least one of the electrodes. Remaining electrodes are grounded as receive electrodes. An ammeter measures electrode current and a measured value corresponding to an operating capacitance of this electrode is acquired and provided in every electrode circuit. Disruption factors are compensated on the basis of these measured values by means of comparison to earlier measured values of the same or of the other electrodes and by means of comparison to specific measured value patterns. An alarm is triggered only given non-compensatable measured values.

Description

The invention relates to a method and an arrangement for measuring capacitive changes in state of a protective fence having a plurality of wire electrodes arranged in parallel, wherein an alternating voltage is applied to at least one of the electrodes and measurement signals are received at at least one electrode, and interference from temporal changes in the measurement signals - or alarm criteria are derived.

It has long been known and customary to determine the intrusion of unauthorized persons into a protected area by means of capacity measurements or by evaluating changes in capacity and to use them to raise the alarm. Capacitive protective fences are used in particular for monitoring extensive open-air systems, since they can be used to reliably detect all changes in condition and thus also the approach and intrusion of unauthorized persons. A problem with such protective fences, however, is that changes in capacity are also caused by interference, in particular by weather conditions, such as rain, snow and frost, but also by birds and small animals, which temporarily sit on the electrodes or slip under the fence. Such interferences should on the one hand not lead to the alarm being given, while on the other hand an intruding person must be reliably recognized and reported in any case. For example, it is known to measure the partial capacitances between the transmitting and receiving electrodes and to evaluate the resulting difference between these partial capacitances via a differential bridge in order to eliminate symmetrically occurring environmental influences (DE-PS 12 20 289). In the case of such bridge circuits, sudden changes in capacitance of a certain size and continuous changes in capacitance with a defined rate of change are used as alarm criteria. With these relatively simple alarm criteria, however, there is only a low level of interference immunity.

It is also already known (DE-OS 31 10 352) to measure the partial capacities and the inherent partial capacities of an electrode system by switching over the potentials of the individual electrodes. The measurement results, namely all system capacities, are evaluated using microcomputers so that a high level of interference immunity is achieved. However, this method has the disadvantage that a large number of complex switching devices must be provided in the vicinity of the electrodes, and that relatively high potentials must be constantly switched between the individual electrodes. In addition, only a partial or own part capacity can be obtained per measurement. Because of the settling times when switching, a complete measurement therefore takes a relatively long time.

In the earlier application P 32 22 640.3 a method has already been described in which the partial and the proprietary. partial capacities of an electrode system can all be measured simultaneously using different frequencies. In this case, too, high interference immunity can be achieved by evaluation using microcomputers. However, this method also has the disadvantage that, because of the different measuring frequencies, a high level of circuitry is required for the transmitters and the receiving devices with appropriate filters.

The object of the invention is to provide a measuring method and an arrangement for measuring capacitive changes in state of the type mentioned at the outset, the circuit complexity for the measurement being considerably reduced compared to the known methods and nevertheless high immunity to interference being ensured.

According to the invention, this object is achieved in that the current intensity is determined as a measurement signal in each of the connected electrodes and a measurement value for the operating capacity of the electrode in question is obtained therefrom, and in that from the change in the measurement values of individual electrodes in comparison with their respective rest value and / or In comparison with the other electrodes, fault or alarm signals can be derived.

With the current measurement according to the invention at the individual electrodes, a number of measured values corresponding to the number of electrodes is obtained and thus a high redundancy of the alarm message. Each measured current value is proportional to the operating capacity of this relevant electrode with a certain connection in the entire electrode system. It is not necessary to determine the individual partial capacities and individual partial capacities.

The measured values corresponding to the number of electrodes can be evaluated via the known properties assigned to the respective electrode. For example, electrode thickenings that occur simultaneously on all electrodes can be identified as an accumulation of water, snow or frost and can be compensated for during the evaluation.

To compensate for uniformly acting interferences, such as the weather influences mentioned, it is expedient to add an average value from the measured values of all electrodes form and compare each individual measured value, which is multiplied by a factor derived from the geometric arrangement, with this mean value. In the case of general weather influences, the difference between the mean value and the individual values provided with a factor must then be approximately zero. However, if this difference deviates significantly from zero for individual electrodes, it can be concluded that there is an object specifically on these electrodes which has changed the capacitance significantly beyond the weather conditions.

For a (human) intruder, there are also characteristic time-current profiles or time operating capacity profiles that differ significantly from the profile of faults. For example, a human's penetration between two electrodes can be distinguished from a bird's placement by comparing the steepness of the current change with given patterns. For the demarcation between a human and a hatching small animal, the fact can be used that the current changes of neighboring electrodes are determined by the mass of the approaching body, so that here too the comparison with predetermined patterns enables a distinction to be made.

For special applications, it can be advantageous to connect all electrodes as transmitter electrodes to the alternating voltage of the transmitter. For a security fence, however, it is generally expedient to switch the electrodes partly as transmitting electrodes and partly as earthed receiving electrodes, with the successively arranged electrodes being switched alternately as transmitting electrodes and receiving electrodes in a particularly advantageous embodiment. A particularly good and redundant alarm statement can be obtained by measuring the transmitter and receiver currents, since for an intruder penetrating the fence, the changes in transmitter and receiver currents are in opposite directions. The evaluation of the current measurements is also particularly simple if the transmitter electrodes are all connected to the same voltage and the receiver electrodes are connected to ground potential.

An arrangement for carrying out the method according to the invention is expediently constructed in such a way that a transmitter device can be connected to one or more electrodes, that current measuring devices for measuring the current intensity are provided in each of the electrodes and that the current measuring devices have an evaluation circuit with comparison devices for comparing the individual measured values with the Measured values of the other electrodes determined at the same time, with the measured values of the same electrode in each case determined earlier. is connected with saved values.

• Fig. 1 die schematische Anordnung eines Schutzzauns mit Sender und Strommeßeinrichtungen,
• Fig. 2 ein Blockschaltbild für die Auswertung der an dem Schutzzaun gewonnenen Meßwerte,
• Fig. 3 eine detailliertere Schaltung der Funktionseinheiten in der Vergleichseinrichtung VG2,
• Fig. 4 ein Diagramm zur Darstellung der Kapazitätsänderungen aufgrund unterschiedlicher Annäherungsgeschwindigkeiten eines Vogels und eines Menschen.
• Fig. 1 zeigt schematisch einen Schutzzaun mit sieben

The invention is explained in more detail below using an exemplary embodiment. It shows

• 1 shows the schematic arrangement of a protective fence with transmitter and current measuring devices,
• 2 shows a block diagram for the evaluation of the measured values obtained on the protective fence,
• 3 shows a more detailed circuit of the functional units in the comparison device VG2,
• Fig. 4 is a diagram showing the changes in capacity due to different approach speeds of a bird and a human.
• Fig. 1 shows schematically a protective fence with seven

Electrodes that are alternately connected one above the other as transmitting electrodes and as receiving electrodes in the order of their arrangement. The transmitting electrodes 1S, 3S, 5S and 7S are all connected to a common alternating current transmitter S, which generates an alternating voltage U _s of, for example, 100 V and 10 kHz. The receiving electrodes 2E, 4E and 6E, however, are all connected to ground potential. Each electrode has an intrinsic capacitance compared to the earth potential, for example, the electrode 1S has the capacitance C ₁₁ or the electrode 7S has the intrinsic capacitance C ₇₇ . There are partial capacitances between the individual electrodes, for example capacitance C ₁₂ between electrodes 1S and 2E or capacitance C ₅₂ between electrodes 5S and 2E.

One of the current measuring devices IM1 to IM7 is switched into the circuit of each electrode 1S to 7S, the current ^I _{1S '} ^I _2E ••• to I _7S flowing in the respective transmitting or receiving ^{electrode being present} when the transmission voltage U _{s is applied} the transmitter electrodes are measured This means that a potential switchover is not required when measuring, and a single transmitter frequency is also sufficient. The current measured in the respective electrode is proportional to the operating capacity of this relevant electrode. For the example shown in FIG. 1, the following applies to the individual currents with the same transmission voltage U _S :

The sum of the respective partial capacities and own partial capacities in parentheses is the operating capacity for the electrode in question. With a system With the method according to the invention, n currents or n operating capacitances Cp of μ = 1 ... n are measured from n electrodes. From this, n measured values can be obtained for further evaluation. It is therefore not necessary to determine the individual partial capacities or own partial capacities.

FIG. 2 shows in a block diagram the evaluation of the measurement signals obtained according to FIG. 1. From the current measuring device IM, which contains, for example, the seven current measuring devices IM1 to IM7 from FIG. 1, the seven current measured values are passed over a bandpass filter BF for further evaluation in order to switch off higher-frequency processes. For example, the bandpass filter covers a range from 0.0001 Hz to about 10 Hz. The current measuring device IM can of course also contain a single measuring device instead of the individual measuring devices IM1 to IM7, with which the seven electrodes are scanned using multiplex technology. With each scan, the new measured values are compared in a comparison device VG1 with the earlier measured values of the same electrodes contained in a memory SP1. If the values are unchanged from the previous values or rest values, there is no need for further processing. However, the measured values are stored for a certain time, so that a certain number of comparison measured values from previous samples are available.

If the measured values have changed compared to an earlier scan, the comparison device VG1 generates a signal for the further comparison devices VG2, VG3 and VG4. When this signal is present, the measured values for the operating capacities C _µ (µ = 1 ... 7) are fed from the comparison device VG1 or via the memory SP1 to the further comparison devices VG2, VG3 and VG4. In these comparison devices, alarms criteria derived from different points of view.

The mode of operation of the comparison device VG2 can be seen from FIG. 3. With the signal from the comparison device VG1, the measured values of the operating capacitances C _{μ are} passed to a first arithmetic circuit RE1 via an AND gate AN1. In this arithmetic circuit, an associated wire diameter D is calculated for each operating capacity. The wire diameter is a function f _µ of the operating capacity C. This function is different for each wire. Therefore, when the system is set up, these functions f (C _µ ) are determined experimentally for each electrode and stored in the calculation circuit RE1. As long as the electrodes are unchanged, the actual electrode diameter D results in the computing circuit RE1. This electrode diameter can increase due to weather influences, for example due to the formation of frost, which results in a corresponding change in the measured operating capacity. However, the operating capacity can also change due to other influences, such as the placement of a bird or the penetration of a human being, in such a way that an apparently enlarged electrode diameter is calculated in the computing circuit RE1.

From the electrode diameters D _µ ( _µ = 1 ... 7) calculated in the calculation circuit RE1, an average is then formed in the mean value generator MB, specifically according to the relationship

Dieser Mittelwert D_m wird dann einer zweiten Rechenschaltung RE2 zugeführt.

This mean value D _m is then fed to a second arithmetic circuit RE2.

In the second arithmetic circuit RE2, the mean value D _m is in turn converted into a value for the operating capacity for converted every single electrode, according to the relationship C'µ = g (D _M ).

The function g _μ is the inverse of the function f _μ described above for each individual electrode and, like this, denotes the dependence between the electrode diameter and the operating capacity for the normal state of the individual electrodes. The values for g for _µ = 1 ... 7 are determined experimentally like the values for f for the system in the normal state or calculated from f and stored in the calculation circuit RE2. There, the value C '= g (D _M ) is now formed from the average electrode diameter D _M via the function g _µ for each electrode and subtracted from the measured value for the operating capacity C _µ . This results in a compensated measured value of the operating capacity C _uk for each electrode. This compensation of the measured values via the described averaging and subtraction results in a value of approximately 0 for all electrodes, as long as there is a uniform thickening of the electrodes due to weather influences. However, if the difference, ie the compensated value C _uk , _differs significantly from 0 or a threshold value C _Sµ in the case of individual electrodes, an intruder can be identified from this. For this purpose, the values C _{µk are fed to} a comparator device KO in which a threshold value C _{Sµ is} stored for each electrode. If it is found in the comparator _device that a value C _{µk is} greater than the associated threshold value S _Sµ , a signal vg2 is emitted at the output.

In order to be able to further differentiate whether the intruder identified is a bird, a small animal or a human, the measured values C _{μ of} the individual electrodes are fed to further comparison devices VG3 and VG4.

In the comparison device VG3, the slope of the change in the measured value is determined by comparison with the stored measured values from the previous scans from the memory SP1 and compared with a predetermined pattern. This evaluates the fact that, for example, a bird approaches the fence much faster than a human can.

wird hier das Alarmkriterium vg3 abgeleitet.4 shows a diagram for this, a typical course of the operating capacity C being plotted over time. The curve C _µV represents the course of the measured value when a bird is approaching it. A steep increase in the operating capacity C is determined between the two measuring times T _m and T _{m + 1} . The operating capacity then remains the same until a steep drop in operating capacity indicates that the bird is flying away at a later point in time. In comparison, the curve for the approach of a person crawling under the fence, for example, shows a completely different course. The curve C _µM shows a relatively slow rise between the times T _m and T _{m + 1} and, accordingly, a slower fall again at a later point in time. In the comparison device VG3 (FIG. 2), a signal is therefore derived from the approach speed of the intruder, ie from the time course of the change in C _μ , in comparison with a threshold value v _S. From the condition

the alarm criterion vg3 is derived here.

wird das Alarmkriterium vg4 abgeleitet, falls die Änderung der Betriebskapazität aufgrund der Masse des eindringenden Körpers über dem Schwellenwert liegt.In the comparison device VG4, the changes in the measured values determined in comparison with the previous scans are compared with stored sample values. These sample values set a limit for the alarm where the mass and the measurement value caused by this mass Change in the pattern of a small animal or bird compared to the pattern caused by the mass of a human body. This is done in a simple manner by comparing the absolute measured value change Δ C _μ corresponding to the mass of the intruder with a threshold value cs. The threshold value for the receiving electrodes and for the transmitting electrodes can be different. This threshold value or these threshold values are also determined experimentally for the relevant plant and stored in the comparison device VG4. With each query, the relationship can

the alarm criterion vg4 is derived if the change in operating capacity due to the mass of the penetrating body is above the threshold value.

An alarm signal AL is only triggered via the coincidence element AN2 when the determined changes in measured values cannot be fully compensated for either by the mean value compensation in the comparison device VG2 or by the steepness-related compensation in the comparison device VG3 or in the delimitation compensation of the comparison device VG4.

In addition, a sabotage detection SE is also provided in a manner known per se, as shown in FIG. 2. This sabotage detection device SE is supplied with both the measured current values from the current measuring device IM for the individual electrodes and the measured voltage value at the individual electrodes. A measuring device UM is used for voltage measurement, which can be connected via a sampling switch AS to the individual electrodes 1S to 7S with each query. If it is found in the sabotage detection device SE that the voltage drops sharply or approaches 0 or that the If the electrode current I _µ goes to 0 at one of the electrodes, a short circuit or a wire break is recognized and evaluated to generate a sabotage signal SAB.

The described evaluation of the measured values is expediently carried out by a microcomputer in which the respective measured values and the values required for comparison are stored and which carries out the comparison operations.

Claims (12)

1. A method for measuring changes in capacitance on a protective fence having a plurality of wire electrodes arranged in parallel, wherein an alternating voltage is applied to at least one of the electrodes and measurement signals are received at at least one of the electrodes, and disturbance or alarm signals are derived from changes in the measurement signals over time, characterized in that in each of the connected electrodes (1S, 2E, ... 7S) the current strength (I1S to I _7S ) is determined as a measurement signal and a measurement value for the operating capacity of the electrode in question (1S to 7S) is obtained therefrom and that fault or alarm criteria are derived from the change in the measured values of individual electrodes with respect to their respective rest values and / or with respect to the other electrodes. 2. The method according to claim 1, characterized in that an average value is formed from the measured values of all electrodes (1S to 7S) and that an alarm signal is derived from the comparison of the individual measured values multiplied by a geometrically determined factor with the average value with significant deviation . 3. The method according to claim 2, characterized in that for averaging from the operating capacities the electrode diameters to be assigned to the individual electrodes is calculated and from this the mean is formed for comparison with the calculated individual diameters multiplied by their respective factor. 4. The method according to any one of claims 1 to 3, characterized characterized in that the steepness of change of the measured values of individual electrodes is determined and compared with predetermined patterns. 5. The method according to any one of claims 1 to 4, characterized in that the absolute change in the measured values of adjacent electrodes is determined and compared with predetermined patterns. 6. The method according to any one of claims 1 to 5, characterized in that all electrodes are switched as transmitting electrodes. 7. The method according to any one of claims 1 to 5, characterized in that the electrodes arranged in succession are switched alternately as transmitting electrodes (1S, 3S, 5S, 7S) and as receiving electrodes (2E, 4E, 6E). 8. The method according to any one of claims 1 to 7, characterized in that the transmitting electrodes are all connected to the same voltage and the receiving electrodes are connected to ground potential. 9. The method according to any one of claims 1 to 7, characterized in that a part of the electrodes is acted upon with a voltage opposite the transmission voltage (U _S ). 10. The method according to any one of claims 1 to 7 and 9, characterized in that the transmitter electrodes are operated with different voltages, for example with staggered voltages. 11. Arrangement for performing the method according to claim 1, characterized in that a transmitting device (S) is connected to one or more electrodes (1S, 3S, 5S, 7S), that current measuring devices (IM1 to IM7) for measuring the current in the circuit of each electrode (1S, 2E, 3S, 4E, 5S , 6E, 7S) are provided and that the current measuring devices are provided with an evaluation device with comparison devices for comparing the measured values with an average value (VG2), for comparing the rate of change of the measured values with a predetermined pattern (VG3) and for comparing the measured value changes with predetermined patterns (VG4) is connected downstream. 12. The arrangement according to claim 9, characterized in that one of the comparison devices contains arithmetic units for calculating the electrode diameter from the operating capacities, for forming an average of the electrode diameter and for subtracting the electrode diameter multiplied by an individual factor from the average.

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