ARRANGEMENT FOR THE CONTACT-LESS TESTING OF THE PRESENCE OF AN ELECTRICAL VOLTAGE

Abstract: An arrangement for the contact-less testing for the presence of an electrical voltage in an electrical conductor or component. The arrangement comprises a sensor device (21), exhibiting an electrical conductor of a specified length, one end (22) of which is open, a first amplifier stage (24), to the input of which the opposite end (31) of the sensor device is connected, and a second amplifier stage (26), the input (32) of which is connected to the output (25) from the first amplifier stage. The second amplifier stage exhibits an indicator device (20) which, when an electric current is induced through the sensor device, will indicate the presence of an electrical voltage in the aforementioned component within a specified sensing area in the vicinity of the sensing device.

Description: Arrangement for the contact—less testing of the presence of an electrical voltage Techni ca I Field: The present invention relates to an arrangement for the contact—less testing of the presence of an electrical voltage in an electrical conductor or component. Technical Problem: There are available portable test devices for the contact—less testing of the presence of an electrical voltage, for example for finding concealed electrical conductors. The commercially available devices sense the magnetic field, however, which requires a current to be flowing through the conductor, that is to say a current consumer must be connected. Furthermore these devices are not, as a general rule, so selective as to permit them to be used for checking whether a single fuse in a group installation is defective because of the positioning of the fuses adjacent to one another. Previously disclosed devices can thus wrongly indicate the presence of a voltage as a result of the interference of the magnetic field of an adjacent fuse. The object of the present invention is to propose an easily handled arrangement by means of which the disadvantages referred to above are eliminated. The Solution: The aforementioned object is achieved by means of an arrangement in accordance with the present invention, which is characterized in that the arrangement comprises a sensor device, exhibiting an electrical conductor of a specified length, one end of which is open, a first amplifier stage, to the input of which the opposite end of the sensor device is connected, and a second amplifier stage, the input of which is connected to the output from the first amplifier stage, in addition to which the second amplifier stage exhibits an indicator device which is so arranged as to -indicate the presence of an electrical voltage in the aforementioned component within a specified sensing area in the vicinity of the sensor device, and in that the second amplifier stage contains a rectifier so arranged, in the presence of a detected voltage in the aforementioned electrical component, as to conduct an electrical current through the indicator device for the purpose of the actuation of same. Brief Description of the Drawings: The invention is described below in greater detail in relation to a couple of illustrative embodiments with reference to the accompanying drawings, in which Fig. 1 shows a side view of a test arrangement in accordance with the invention as a first illustrative embodiment; Fig. 2 shows a schematic longitudinal section through the arrangement in accordance with Fig. 1; Figs. 3 and 4 show corresponding views of the test arrangement in accordance with a second illustrative embodiment; Fig. 5 shows a connection diagram for the arrangement in accordance with the invention; and Fig. 6 shows an example of the application of the arrangement. Preferred Embodi ent: A first example of the mechanical construction of the test arrangement can be appreciated from Figs. 1 and 2. The test arrangement can be given an extremely compact construction similar in shape to a pen with a tubular casing 1 and an attachment clip 2 for securing the arrangement in a pocket or similar. The main part of the space inside the test arrangement is taken up by a current source consisting of two series—connected batteries or accumulators 4, with one of the poles of one of the batteries, usually the positive pole 6, connected to an electronic circuit 7 via a switching device 8. The other pole . of the other battery, i.e. in this case the negative pole 9, is connected via a spring element 10 to the electrically conducting casing 11 in a similar fashion to the arrangement used in a flashlight. A detachable end plug 12 supports the spring element 10 and can be removed to permit replacement of the batteries. In the example shown here the electrical circuit with its zero potential connection (see below) is connected to the conducting casing and is intended to be situated in a cylindrical component 13 made of an electrically insulating material, for example of moulded plastic with an opaque body 14. This cylindrical component can be assembled in a detachable fashion with the tubular electrically conducting component 11 by means of a threaded section 15. At the front end of the test arrangement, which constitutes the sensing tip 16, there is provided a conical part 17 which is translucent and is provided with, for example, a facetted surface 18. The conical part 17 exhibits more precisely the form of a truncated cone with a preferably flat end surface 19. The conical part 17 houses an indicator device 20 which, in the example illustrated, is of an optical type in the form of, for example, a light emitting diode capable of being switched between a lit and an extinguished state. Also housed inside the conical part 17 is a sensor device 21 which exhibits a free, i.e. an open ' end 22, situated behind the end surface 19, and an end 23 connected to the electrical circuit 7. The facetted surface 18 is formed by the prism grinding process and acts as a lens for the light emitted by the light emitting diode in its lit state. The sensor device 21 consists of an electrical conductor of precisely determined length. Figs. 3 and 4 show a second embodiment of the test arrangement. This differs from the first embodiment essentially in that it is executed as a lamp with a bulb 42 situated between the batteries 4, 5 and the electrical circuit 7. This is situated in a slightly protruding translucent and preferably knurled section 43, in which case a separate bulb is not required. The switch for the bulb and possibly also for the electrical circuit 7 may be built into the clip 2, for example. The layout of the electrical circuit 7 in accordance with a proposed example may be appreciated from Fig. 5. The electrical circuit 7 in actual fact represents the test arrangement as such, although other components have been included to permit the practical function of the arrangement. The electrical circuit 7 and thus the test arrangement itself is constructed from a first amplifier stage 24 and a second amplifier stage 26 connected to the output 25 from the first amplifier stage. The source of current 4, 5 is intended to be connected by its positive pole to the positive connection point 27 and to be connected by its negative pole to the negative connection point 28, which also constitutes the 'earth' for the arrangement, that is to say its zero potential. The first amplifier stage 24 consists in the example shown of a so—called Darlington pair of two transistors 29, 30, which are thus connected together in a Darlington arrangement, as shown in the Figure. The sensor device 21 in the form of the electrical conductor is, as stated above, free or open at one of its ends, that is to say it is not connected electrically to anything, and is connected at its other end to the base 31 of the first transistor 29 in the first amplifier stage 24. Also included in the circuit is a resistance 33 of, for example, 10 ohms connected between the output 25 of the first amplifier stage and the input 32 of the second amplifier stage 26, and a resistance 34 of, for example, 2 kiloohms, connected between the input 32 of the second amplifier stage and its positive connection point 27. Also included is a capacitor 35 of, for example, 1 microfarad. The principal component parts of the second amplifier stage 26 consist of a transistor 36 and the indicator device 20 in the form of the light—emitting diode. The particular design of the test, arrangement with an open base allows the sensor device 21 to act as an antenna which senses the electrical field in an electrical conductor or component. In this way the test arrangement provides an indication of electrical voltage, irrespective of whether or not a current is flowing through the conductor or the component. This is extremely important, for example, for checking whether or not fuses are defective. Experience has shown that .the procedure of checking fuses simply by examining the coloured end—plate of a fuse is very unreliable, since the plate will often remain in its position even if the fuse has blown and the conductive wire present inside the fuse has melted. The sensitivity of the arrangement for such an application is adjusted so that the arrangement will not sense the electrical field from any adjacent fuses, or from one side of the fuse holder which will, of course, remain electrically conductive when a fuse blows. The test arrangement is used in such a way that the rod— or perr-shaped arrangement is pointed at the fuse 37 in question which is to be tested in a group installation 38, and more specifically with its sensing tip 16 positioned relatively close to or against the inspection glass 39 in the fuse holder 40; see Fig. 6. Indication of whether a fuse is defective or sound is achieved simply by activating the indicator device 20 and switching it from a first state to a second state,in the example illustrated here by the light—emitting diode lighting up, if the fuse is sound and if a voltage is accordingly present at the end of the fuse situated closest to the sensing tip 16. When the light-emitting diode is extinguished, the input 32 to the second amplifier stage 26, that is to say the control electrode in the form of the base of the transistor 36, will exhibit a potential such that the transistor 36 is open, that is to say that a current will not flow in the circuit indicated by the arrows 41. When the test arrangement is held up to the fuse 37 which is to be tested, nothing will happen if the fuse is defective, since in this case no electrical field will be present at the sensor device 21 of such a strength as to cause an indication to be given. This is the case because only that end of the fuse furthest away from the test arrangement will exhibit a voltage, that is to say the part situated in the bottom of the fuse holder 40. The sensitivity of the arrangement is thus adjusted in such a way that it will not react to the electrical field at a distance of about the length of a fuse. This is true at least in the presence of a mains voltage of 1.10-380 V. If the fuse is sound, which means that the fuse is also live at its end situated closest to the sensing tip 16, an electrical field will be present at the sensor device 21 of such a strength that a potential difference will occur in the conductor which acts as an antenna, which constitutes the sensor device 21, said potential difference being amplified in the first amplifier stage by the transistors 29, 30 changing state with regard to their conductivity, which in turn gives rise to a potential difference at the input 32 to the second amplifier stage 26, that is to say the control electrode in the form of the base of the transistor 36, due to the discharge of the capacitor 35, in which case the transistor 36 will change its state of conductivity from a cut—off state to a conductive state, with the result that a current will flow in the direction of the arrows 41 from the positive pole 27 through the light—emitting diode 20 and to the negative pole 28, in which case the light—emitting diode will be caused to light and the conical part 17 will be imparted with an even, strong light because of the prism—ground surface. The light—emitting diode may, for example, be of the high—intensity light—emitting diode type, enabling a clear indication to be seen even in daylight conditions. When the test arrangement is moved away from the fuse, the light—emitting diode will -be extinguished rapidly because of the change in the state of the conductivity of the Darlington transistors, since the absence of electrical field strength will once more produce a potential difference in the sensor device 21 executed as an open base. This in turn will cause a change to occur in the potential at the base 32 of the transistor 26, thereby cutting off that transistor, which will thus act as a rectifier. There is no need for the circuit to be closed via the human body, as a result of which the arrangement can, if so desired, be executed with an insulated casing. The invention is not restricted to the illustrative embodiments described above and illustrated in the drawings, but may be modified in a number of ways within the scope of the following Patent Claims. For example the antenna, that is to say the sensor device 21, can be directed by means of a screened antenna with a screen which is connected to the negative pole 28. In this way the antenna is less sensitive in an angular sense, that is to say to electrical fields from conductors which are situated alongside the test arrangement in its longitudinal sense. The screen can be executed in such a way that it is capable of being connected and disconnected for the purpose of varying the sensitivity. The length of the sensor device 21 as such can also be selected so as to provide the desired sensitivity so that the test arrangement will not react to the electrical field from adjacent fuses. The arrangement can also be equipped with two sensor devices of different lengths, which may be connected alternately so as to provide a choice between two levels of sensitivity. No manually operated change—over switch for the current source is required, since the arrangement uses practically no current at all when the transistors are cut off and the light—emitting diode is thus extinguished, as far as the embodiments in accordance with Figs. 1 and 2 are concerned. A change—over switch may be included, however, as a safety measure. In the interests of clarity it must be pointed out that the expression 'contact—less' is used to denote that the test arrangements do not require to be brought into contact with the electrical conductor or component which is'to be tested.

Claims: Pa t e n t C l a i s: 1. An arrangement for the contact—less testing of the presence of an electrical voltage in an electrical conductor or component (37 ) , c h a r a c t e r i z ed in that the arrangement comprises a sensor device (21), exhibiting an electrical conductor of a specified length, one end (22) of which is open, a first amplifier stage (24), to the input of which the opposite end (31) of the sensor device is connected, and a second amplifier stage (26)^ the input (32) of which is connected to the output (25) from the first amplifier stage, in addition to which the second amplifier stage exhibits an indicator device (20) which is so arranged as to indicate the presence of an electrical voltage in the aforementioned component within a specified sensing area in the vicinity of the sensor device, and in that the second amplifier stage (26) contains a rectifier (36) so arranged, in the presence of a detected voltage in the aforementioned electrical component, as to conduct an electric current through the indicator device (20) for the purpose of the actuation of same. 2. An arrangement according to Patent Claim 1, c h a r a c t e r¬ i z e d in that the indicator device consists of a light—emitting unit, preferably a light—emitting diode. 3. An arrangement according to any of the preceding Patent Claims, c h a r a c t e r i z e d in that the first amplifier stage (24) is so arranged as to produce very high current amplification. 4. An arrangement according to Patent Claim 3, c h a r a c t e r¬ i z e d in that the first amplifier stage (24) consists of two transistors connected together in a Darlington arrangement, with a first transistor (29) exhibiting an open base through the connection of the base to the opposite end (31) of the sensor device (21) which is open at one end (22). 5. An arrangement according to any of the preceding Patent Claims, c h a r a c t e r i z e d in that the sensor device ( 21 ) exhibits, in addition to an electrical conductor, partially enclosing electrical screening. 6. An arrangement according to any of the preceding Patent Claims, .. c h a r a c t e r i z e d in that the arrangement is constructed in the form of an essentially rod-shaped unit with a long sleeve—shaped component (1), inside which a current source is accommodated, a component situated ahead of the current source, which contains an electrical circuit, and situated ahead of it a sensing tip, which is executed in an electrically insulating material and which contains at least the sensor device (21). 7. An arrangement according to Patent Claim 6, c h a r a c t e r¬ i z e d in that, in the event of the indicator device (20) being an optical device so arranged as to emit a beam of light when indicating, the indicator device is situated in the sensing tip 071-, which in this case is executed in a transparent material. 8. An arrangement according to Patent Claim 7, c h a r a c t e r¬ i z e d in that the sensing tip (.T is essentially conical and tapers in the direction of the end of the arrangement and exhibits a prismatic ground lens surface at the conical generated surface. 9. An arrangement according to Patent Claim 7, c h a r a c t e r¬ i z ed in that the sensing tip. (16) exhibits essentially the form of a truncated cone with an essentially flat end surface (19), behind which is situated the free, open end (22) of the sensor device.

Inventors: NYLEN HARDY, NYLEN, HARDY
Applicants: NYLEN HARDY, NYLEN, HARDY
Application year: 1986
Main classification: G01R19
IPC codes: G01R19