GB2151360A - Apparatus for locating fault points in electric guide loops - Google Patents

Abstract

Apparatus for locating a fault point having increased conductor resistance, such as a break (3),in electric guide loops (2) to which is applied a periodic electrical signal from at least one current generator (1) consists of a movable unit (19) which comprises in one common housing (20) two capacitive sensor plates (6, 7) which are positioned in succession, one after the other. To each one of the plates is connected a device (24) for detection of the presence of a voltage difference between said plates when they are positioned adjacent the loop (2). A device (18) is provided to indicate the occurrence of changes of the condition of said detection involving increased conductor resistance, such as breaks, in any one guide loop (2). <IMAGE>

Description

SPECIFICATION An apparatus for locating fault points having increased conductor resistance in electric guide loops The subject invention concerhs an apparatus for locating fault points having increased conductor resistance, such as breaks, in electric guide loops to which is applied a periodic electrical signal from at least one current generator for the purpose of controlling the movements of loop-guided vehicles along the guide loop.

Apparatuses for locating interruptions in conductors are previously known which utilize a capactive coupling for detection purposes.

However, these apparatuses are not freely movable units but are connected to the electric loop via a cable in order to obtain a reference signal in response to the phase position of the periodic voltage in the loop. It is obviously possible to replace the cable connection by wireless transmission but to do so would involve a considerable rise in costs and increased sensitivity to disturbance.

The purpose of the subject invention is to provide an apparatus which does not have the deficiencies outlined above and is easy to handle, reliable and may be produced at comparatively low costs.

These objectives are met in an apparatus in accordance with the subject invention which is characterised in that it consists of one single, competely freely movable unit which in a common housing comprises at least two capacitors which are positioned in succession, one after the other, spaced a fixed distance apart, a first device which is connected to each one of the two capacitors for detection of the presence of any voltage difference between the two capacitors and a second device for indication of any changes of the condition of said detection involving increased conductor resistance, such as breaks or similar faults in any one of the guide loops.

The invention will be described in closer detail in the following with reference to the accompanying drawings, wherein Figure 1 is a schematic view of an electric guide loop in which the apparatus in accordance with the subject invention may be used, Figure 2 is a block diagram showing the structure of the apparatus of the subject invention in accordance with one embodiment thereof, and Figure 3 illustrates one example of a typical arrangement of an apparatus in accordance with the invention.

Fig. 1 shows a simplified version of an installation wherein the apparatus of the subject invention may be used. The installation consists of a current generator 1 to which is connected an electric guide loop 2. The current generator 1 is designed to emit a periodic- electric current of one or several predetermined frequencies. Loops of this kind are used for example to control the movements of driver-less transportation vehicles, which vehicles are equipped with control devices to sense, e.g. inductively, the magnetic field generated when alternating current is fed through the guide loop 2. In one existing system there are usually a large number of loops which run adjacent one another. By supplying the loops with current of different frequencies from different current generators the control may be made selectively.For this purpose frequencies within the tone frequency range may be used. The loops are generally embedded in the flooring on which the driverless vehicles travel. The current generator 1 comprises one or several oscillators the frequency or frequencies of which determine the frequency of the guide loop 2.

By numeral 3 is symbolically represented a point with an increased resistance in the guide loop 2 which the apparatus in accordance with the invention is designed to locate. The break or fault point 3 can be a non-intended mechanical break in the loop or be a point with increased resistance which brings about such changes of the electricity properties of the loop that the latter is rendered at least partially non-operational. The increased resistance can appear in a joint connection having poor electrical contact between its contact surfaces. To locate the fault point is difficult and calls for special means and the apparatus in accordance with the subject invention offers one advantageous solution to this locating problem.The fault results in an increased resistance up to infinite magnitude in the loop, whereby the voltage signal in one section 4 of the loop on one side of the fault of break point is given an increased amplitude, whereas the signal decreases or disappears in the other section 5 of the loop on the opposite side of the break point, which generally is connected to earth. At the same time, owing to the increased or infinite resistance in the loop the current generator is overamplified and in consequence thereof the signal, which normally is essentially sinusoidal, is converted to a square wave shape, resulting in the generation of a large number of overtones.

The apparatus in accordance with the invention is designed to make use of the change in the electrical condition of the loop referred to above to locate the fault or break point 3 in the guide loop 2.

Fig. 2 shows schematically the structure of the apparatus in accordance with the invention. As appears from Fig. 2 the apparatus in accordance with the invention comprises two capacitors 6, 7 which are arranged in succession, one after the other and are intended to be moved along the guide loop 2 in such a manner that each capacitor will be placed above the guide loop. The two capacitors 6, 7 are incorporated in a differential capacitor which is connected to each one of the two inputs 8, 9 of a differential amplifier 10. To the output 11 of the differential amplifier 10 is connected the input 1 2 of a rectifier 1 3 to the output 14 of which is connected the input 1 5 of an amplifier 16.The output 1 7 of the latter is connected to an indicating instrument 1 8 in the form of a voltmeter. The differential amplifier 10, the rectifier 1 3 and the amplifier 1 6 together form an apparatus 24 for detection of voltage differences.

As appears from Fig. 3 all the components described with reference to Fig. 2 are enclosed in one single unit 1 9 which is intended to be moved along the guide loop 2. The unit 1 9 is constructed as a closed box-shaped housing 20 having a handle 21 of preferably the same dimensions as a conventional broomstick in order to allow the apparatus to be handled and displaced conveniently across a floor. Fig. 3 shows the cover 29 in a crosssectional view with the apparatus interior being represented entirely schematically. The boxshaped cover can either be an openbottom cover or be equipped with a bottom wall 22 of an electrically non-conductive or nonscreening material, at least in the area opposite the capacitors 6, 7.The capacitors consist of two plates which are positioned at the same level in the housing 20 and extend in one and the same plane. This plane is to extend in parallel with the plane of the substratum 23, usually a floor across which the apparatus is displaced. In addition, the capacitor plates 6, 7 are positioned in alignment and thus not in laterally offset relationship in their own plane, that is, across the plane of the drawing figure paper sheet. Furthermore, the cover of the unit 1 9 also encloses the detector device 24.Batteries or accumulators preferably are used as the source of power for the electronic equipment in the unit 1 9. The indicating instrument 1 8 thus is connected to the detecting device 24, said indicating instrument being a device designed to indicate the occurrence of a point or points of a break or other conductive fault in a guide loop 2. The indicating instrument 1 8 is mounted in the housing 20 so as to be easily readable by the user.

The apparatus in accordance with the invention operates in the following manner. Upon occurrence of a suspected break or fault in a guide loop 2 the locating apparatus in accordance with the subject invention, that is, the unit 19, is pulled out and is moved along the guide loop 2 in such a manner as to ensure that the unit is displaced along the loop in the direction indicated by arrow 25. In other words, the apparatus is moved in such a way that the two capacitor plates 6, 7 will be positioned one after the other in succession as seen in the longitudinal direction of the loop 2, that is, in the direction of arrow 25. One ofthe ends of the guide loop 2 is chosen as the starting point and it is of no importance which end that is chosen.However, should a particular section of the guide loop be suspected to be the one where the fault exists, another point could, of course, be chosen as the starting point. The locating apparatus 1 9 is not connected by a cable to any fixed portion but is a freely movable unit utilizing only the capacitive coupling between the capacitors 6, 7 and the guide loop section 5. Owing to the comparative proximity of the capacitor plates 6, 7 to the loop section 5 the plates are charged by the electro-magnetic field which is generated around the guide loop 2 when the latter is connected to the current generator 1 which aims at emitting electric current. Upon the occurrence of a break, the current is cut off, whereas the other loop section 4 still is energized.The two capacitor plates 6, 7 are charged up to a predetermined voltage under the influence of the field generated by the alternating voltage present in the guide loop 2. On the side of the break point in the loop which is connected to earth and therefore is de-energized, the voltage of the capacitor plates 6, 7 is zero, that is, equal voltage, and the differential amplifier 24 therefore detects voltage difference zero and does not emit an output signal across the output 11. Consequently, the indicating instrument 1 8 shows no reading.Conditions remain the same as long as the locating apparatus is being moved along the guide loop on the opposite side of the point of break or fault 3, since in this case the capacitor plates 6, 7 receive approximately equal voltage loads and consequently the differential amplifier 10 still emits output signal zero and the indicating instrument 1 8 still shows substantially no reading. In case the apparatus 1 9 is turned or lifted at an angle some small voltage difference might occur but this will only result in a minor reading.

When the apparatus in accordance with the invention passes a point of break or fault the following sequence of events will take place when the capacitor plates 6, 7 assume the position shown in Fig. 3. The capacitor plate 6 which is positioned above section 4 of the energized guide loop is loaded to a predetermined voltage, while the other capacitor plate 7 which is positioned above the loop section which is de-energized is not similarly loaded or possibly is loaded to a considerably lower voltage than is capacitor plate 6. Some minor loading may occur under the influence from the field generated in the energized loop section 4 or in a case where complete interruption is not present, but for example a poor contact in a joint. Consequently, different voltages are applied to the two input terminals 8, 9 of the differential amplifier 10, with the result that an output signal is emitted from the amplifier output which is rectified by the rectifier 1 3 and amplified by the amplifier 16 and thereafter produces a significant reading in the indicating instrument 18. When the apparatus has been moved past the break point 3 and the two capacitor plates 6, 7 are again positioned on the same side of the break point, they again receive essentially equal voltage and the indicating instrument 1 8 therefore returns to substantially zero.

The apparatus may be used also when several guide loops are positioned closely adjacent one another and one of them is suspected to have a break or fault point 3 therein. The reason therefore is that the capacitor plates 6, 7 will always have different voltages as soon as a break or fault occurs.

The locating operation is facilitated because, as mentioned in the aforegoing, a fault or break results in an increased resistance up to infinite magnitude in guide loop 2 and therefore in a larger voltage amplitude in the fully energized loop section. Because of the overamplification of the current generator 1 with an increased share of overtones the detection work is further facilitated.

From a mechanical point of view the locating apparatus 1 9 thus is moved across the support or substratum 23 in which the guide loop 2 is embedded. The displacement may be effected by the operator grasping the handle 21 to move the apparatus in front of himself, allowing the apparatus to slide with its lower face 26 in contact with the support.

In this case the lower face 26 should be in the form of a low-friction wear-resistant surface. Alternatively, wheels, rollers or the like may be used.

The invention is not limited to the embodiment described above and illustrated in the drawings but may be modified in a variety of ways within the scope of the appended claims. In the aforegoing has been described an embodiment according to which one end of the guide loop 2 is connected to earth in such a manner that one side 5 of the loop experiences voltage disappearance upon loop breaks or faults. However, it is entirely within the inventive idea to design the current generator 1 in such a manner that also this section 5 of the loop is energized in the event of a capacitor fault. The apparatus in accordance with the invention is operational also in such cases, since the two sections 4, 5 of the guide loop 2 then receives voltage signals with difference in phase.The result is that at every moment the two capacitor plates 6, 7 on one or the other side of the break point receives equal voltages, and therefore there is no or only an unsignificant reading in the indicating instrument 1 8 whereas at every moment, when the capacitor plates 6, 7 are positioned on different sides of the point of break or fault, they exhibit a voltage difference which results in a definite reading in the indicating instrument 18. In addition indication of a located point of break or fault may be registered by other means than an indicating instrument. For instance, the indicating instrument 1 8 may be replaced by an optic or accoustic indicating instrument which is activated whenever the voltage exceeds a predetermined threshold value, thus eliminating voltage changes caused by careless handling of the apparatus. The apparatus may also be used to locate faults in other electric guide loops, such as loops designed to guide busses, trolleys and similar vehicles into stoppingplaces. However, the apparatus is not limited to the uses referred to above but may be used in electrical guide loops generally in which periodic electrical signals occur.

Claims (6)

1. An apparatus for locating a fault point (3) having increased conductor resistance, such as a break, in electric guide loops (2) to which is applied a periodic electrical signal from at least one current generator (1) for the purpose of controlling the movements of loopguided vehicles along the guide loop, characterized in that the apparatus (19) consists of one single, completely freely movable unit which in a common housing (20) comprises at least two capacitors (6, 7) which are positioned in succession, one after the other, spaced a fixed distance apart, a first device (24) which is connected to each one of the two capacitors for detection of the presence of any voltage difference between said two capacitors, and a second device (18) for indication of any changes of the condition of said detection involving increased conductor resistance, such as breaks or similar faults in any one of the guide loops (2).

2. An apparatus as claimed in claim 1, characterized in that the two capacitors are formed by a differential capacitor.

3. An apparatus as claimed in claim 1 or 2, characterized in that said first device (24) comprises a differential amplifier (10) having two inputs (8, 9) each one of which is connected to its respective one of the two capacitors (6, 7), said amplifier arranged to emit across its output (11) a signal to detect the presence of any change of condition of said detection.

4. An apparatus as claimed in claim 3, characterized in that to the output (11) of the differential amplifier (10) is connected a rectifier (13) and an amplifier (16) connected to and in sequence after said rectifier, said indicating device (18) being connected to the output (17) of said amplifier (16).

5. An apparatus as claimed in claim 4, characterized in that the indicating device (18) is a voltmeter.

6. An apparatus as claimed in any one of the preceding claims, characterized in that the two capacitors (6, 7) are capacitor plates positioned in one and the same plane, said plane extending in parallel with the lower face (26) of said housing (20), said plates being positioned in opposite relationship without lateral displacement.