GB1562578A

GB1562578A - Electrical circuit test devices

Info

Publication number: GB1562578A
Application number: GB15591/78A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1977-04-21
Filing date: 1978-04-20
Publication date: 1980-03-12
Also published as: SE7804537L; BE866251A; CA1101072A; JPS6019460B2; DK172978A; FR2388281A1; IT7822519A0; AR213041A1; SE425270B; NL7804231A; IT1094448B; FR2388281B1; JPS53132389A; LU79484A1

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRICAL CIRCUIT TEST DEVICES (71) We, SIEMENS AKTIENGESELLSCHAFT, a German Company of Berlin and Munich, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to electrical circuit test devices for detecting the presence and polarity of an electric potential or performing a continuity test, the device comprising two test probes connected by a cable.

The German Patent Specification No.

2,060,884 describes a test device for indicating the polarity and the phase state of electric potentials relative to a given reference potential, wherein two luminescence diodes are connected in parallel with opposite polarities, and a series current limiting resistor is provided. The two luminescent diodes are disposed by a protective window in a pencil-like housing of a test probe which also contains the series current limiting resistor and has a metal point at one end.

The two luminescence diodes are connected via the currenet limiting resistor between the metal point and a test line which leads out of the pencil-like housing. When testing the presence of a d.c. voltage causes one or the other of the luminescence diodes to be illuminated, in accordance with the polarity, whereas when an a.c. voltage is present then both luminescence diodes are illuminated.

If the current limiting resistor is in the form of a ceramic cold conductor thermistor which, as is known, may consist of ferroelectric material on a base of n-doped and/or p-doped barium titanate, and has a temperature dependence such that in the region of the Curie temperature it exhibits a sudden increase in its electrical resistance by approximately 4 powers of ten, this device can be used to check voltages from approx imately 2 V up to 500 V. The ceramic cold conductor exerts a protective function for the luminescence diodes, as it limits the cur rent if current flow causes self heating to a value above the Curie temperature, with the consequent considerable increase in resis tance.

However, in many cases it is not only necessary to determine whether a device is connected to a current source, i.e. to detect whether a voltage is present and ascertain the nature of the polarity thereof, but it is also desirable to be able to check whether there is continuity of an electric conductor path, so that it can be ascertained whether an electric component, an electric assembly or the like load circuit may be traversed by current when connected to a source. This checking of continuity for the passage of current is often of particular interest, and may be desired when it is not necessary to check voltages.

Current continuity path checking devices operate in accordance with the principle that a current is supplied from a test voltage source to flow throug the electrical conductor path which is to be checked, and an acoustic or optical signal is normally provided to indicate whether there is a passage of current or not.

The U.S. Patent Specification No.

3,870,950 describes an input protection circuit for electric current path continuity checking device which contains a separate current source and a current flow indicator for testing voltage-free circuits, with protection from alien voltages which could jeopardise the current flow indicator, a semiconductor switch and a cold-conductor thermistor being connected in series, with the freeends of probe pins serving as connecting terminals, the current source and the current flow indicator being connected in series between the free ends, one free end being connected via the semiconductor switch and the other via the cold conductor thermistor.

One object of the present invention is to provide a voltage test device of a type known per se for detecting any electric voltage and/or the polarity thereof with further capabilities so that it can readily be used as a continuity test device by the passage of current through an electric conductor path, with adequate protection functions provided to increase the reliability of the device.

The invention consists in an electrical circuit test device for detecting the presence and polarity of an electric voltage, and for conducting a continuity test, said device comprising two probes in the form of handles connected by a cable and provided with contact points, at least one of said handles serving as a housing for circuit components of the device, said components including two luminescence diodes connected in parallel with opposite polarities, which diodes are connected to one contact point via a ceramic cold conductor thermistor, and to the other contact point via a keying switch which normally establishes direct contact, but can be operated to bring into the series path the series combination of a bettary source and a protective diode poled to conduct current from said battery when said contact points are conductively connected during a continuity test.

Preferably the keying switch is arranged in front of a guard ring.

Preferably the keying switch is connected in parallel with a Zener diode.

Advantageously, one handle may contain all the components and the second handle simply serves as a contact point probe.

The invention will now be described with reference to the drawings, in which: Figure 1 schematically illustrates constructional details of one exemplary embodiment of the test device; Figure 2 is a schematic circuit diagram of one exemplary embodiment of the invention; Figure 3 is a schematic circuit diagram of a further exemplary embodiment of the invention; Figure 4 schematically illustrates constructional details of another embodiment of the test device; Figure 5 schematically illustrates details of yet another exemplary embodiment of the test device; Figure 6 shows details of a preferred form of battery housing for use in embodiments of the invention; and Figure 7 is a section along the line IV-IV of Figure 5 showing the battery housing in the extracted position.

In the embodiment shown in Figure 1, the test device consists of two probes in the form of handles 1 and 2 which house the electrical components and electrical connection paths.

The handle 1 contains two luminescence diodes 11 and 12, which are visible from the exterior. A guard ring 13 surrounds the handle 1 to serve as a protection against a user's finger slipping onto a voltage source when a test is being carried out. A metal point 14 at one end of the handle 1 serves as a contact element to connect the test device to a line, component or circuit point which is to be checked. A contact point 15 is provided on the handle 2, and the two handles are connected together by a cable 16.

The handle 2 has a continuous guard ring 17 for protection, similar to the ring 13 of the handle 1. A keying switch 5 is arranged between the metal point 15 and the ring 17.

The handle 2 accommodates a battery 3 and a protective diode 4, and the circuit elements are wired together in accordance with the circuit diagram shown in Figure 2.

The battery, the protective diode and the keying switch 5 can all be accommodated in the handle 1, so that the handle 2 is a simple test probe, as shown in the embodiments illustrated in Figure 4 and 5.

In the circuit diagram shown in Figure 2, the terminal points 14 and 15 correspond to the metal contact points of the test device.

The ceramic cold conductor thermistor 18 is connected in series with the parallel arrangement of the oppositely poled luminescence diodes 11 and 12 to the keying switch 5, which in the rest position 9 is connected to a direct connection line leading to the metal contact point 15. The keying switch 5 is spring-loaded, and is depressed manually to effect a continuity check so that contact is made with a switch terminal 8 to bring a battery 3 into circuit in series with a protective diode 4. The battery 3 has a positive pole 7 and a negative pole 6, and the diode 4 is poled to conduct current from the battery if there is a continuous conductive path present when making a continuity check.

The operation of the device is as follows.

For a voltage check, the keying switch is left in its rest position, so that any voltage difference presented to the metal contact points flows via the thermistor and one of the luminescence diodes, to cause it to glow, the particular diode indicating the polarity of the potential. If an a.c. potential is present, then both diodes glow. An excessively high potential will cause the thermistor to be heated above its Curie temperature so that its resistance rises rapidly, and so protects the diodes from damage.

For a continuity check, the metal contact points are positioned on the path to be checked, and the keying switch 5 is depressed so that current can flow from the battery 3 if there is continuity, and diode will glow. If an a.c. voltage or d.c. voltage is erroneously connected via the circuit under test during a continuity check, this will be fed in via the metal points 14 and 15 and if of one polarity could produce a charging current and thus a gas discharge in the battery, which could lead to its destruction if it is of encased design. The ceramic cold conductor thermistor provided for the protection of the luminenscence of diodes also serves to protect the battery, and thus has a combined effect which virtually eliminates the danger of destruction, but as the cold conductor requires a specific length of time in order to become high-ohmic by self heating the protective diode 4 is incorporated into the protective circuit to block excessive current flow until the thermistor comes into operation.

The battery 3 may be a primary cell structure or a secondary cell structure, e.g. a 12 V monocell. In place of a protective diode, it is also possible to use another semiconductor circuit element, for example a transistor or a triac arranged to provide a similar protective function.

In the modified circuit shown in Figure 3, which may be used in place of the circuit illustrated in Figure 2 is expanded by the addition of a Zener diode 19 connected across the keying switch 5 to link the bridging parallel line 10 to the adjacent junction of the parallel diode combination.

In practice the Zener diode 19 provides three further protective functions. Firstly, the keying switch 5 is protected from high voltages. Secondly, during the testing of high voltages, mistaken actuation of the keying switch 5 is prevented from leading to breakdown of the battery 3 and/or the protective diode 4. Thirdly, provision is made to ensure there is lighting of a diode during a voltage test, if a voltage is present, even if the keying switch is inadvertently depressed and the test device does not hold a battery, or if its battery is fully discharged. Without such a Zener diode such a combination of equipment failure and operator error could result in the absence of any warning indication which could be a danger as there is in fact a voltage present.

The forwards voltage of the Zener diode 19 should be selected in accordance with the voltage of the battery 3. A Zener diode for 15 V is particularly suitable in the case of battery voltages of less than 15 V, e.g. 12 V.

In the further embodiment shown in Figure 4, the test device again consists of two handles 1 and 2, but the handle 2 contains no circuit components, and merely has the function of bearing the contact point 15, and is provided with a guard ring 17, whereas the handle 1 connected to the handle 2 via the line 16 contains all the components of the circuit illustrated in Figure 2 or Figure 3.

The luminescent diodes 11 and 12 are arranged between the contact point 14 and the guard ring 13, so that they are easily visible. They may be mutually aligned parallel to the longitudinal axis, or transverse thereto.

The handle 1 also possesses the keying switch 5, which is positioned on that side of the guard ring 13 opposite the luminescence diodes 11 and 12, i.e. on that side of the handle 1 which is enclosed by the operators hand, when in use.

Within the handle 1 there is arranged the battery 3, which lies with its poles 6 and 7 engaged between clamping contact springs 20 and 21. The battery 3 is accommodated in a battery container 22 which itself is provided with an opening 23 matched to the size of the battery.

A projection 24 serves to allow the extractable housing 22 to be positively engaged with the wall of the housing 1 when in the inserted state.

In order to extract the battery 3 from the recess 23 of the container 22, the wall thereof is partially removed at one end 25 so that free areas are formed on both sides of the battery end through which the battery can be gripped.

When the container 22 has been extracted, an opening is provided through which the protective components, i.e. the cold conductor 18, protective diode 4, and the Zener diode 19 if provided, are all accessible from the exterior, for repair or replacement.

In the alternative embodiment shown in Figure 5, the test device again consists of two handles 1 and 2 very similar to the embodiment shown in Figure 4.

Figure 6 illustrates details of the battery container 22 with the cylindircal cavity 23 in which the battery 3 can be accommodated.

The cavity 23 is partially closed at the lefthand end 30, as drawn, in such manner that only the positive pole 7 of the battery passes through opening 31. At the other end, the opening of the cavity 23 corresponds to the cross-section of the battery 3. The length of the cavity 23 between the ends 30 and 32 corresponds exactly to the length of the battery less its positive pole 7, so that if the battery is incorrectly inserted into the recess 23, the positive pole 7 projects towards the right. If the housing 22 were then impressed into the opening 26 (Figure 5) of the handle 1, the positive pole 7 would prevent complete insertion, because it projects beyond the outer dimensions of the container 22.

As shown in the cross-section shown in Figure 7, the container 22 can be fully removed from the handle 1, for example, when the device requires to be serviced.

However, the container cannot be readily extracted during normal use, because this is prevented by the projections 27 (Figure 6).

In place of the projections 27 it is also possible to provide a bead 28 which extends along the entire length of the container 22.

Since, when the container 22 is in this limited state of extraction, in accordance with Figure 7, the opening 26 remains closed to prevent access to the interior, so that it is not normally possible to touch the contact 20 or the contact 21. The projections serve to lock the container 22 in the fully inserted state.

It is most advantageous to install the container 22 into the handle 1 when this handle is itself assembled. The handle 1 in this embodiment consists of two halves 33 and 34, as indicated in Figure 5 and Figure 7, which are screwed together or firmly glued to one another in a plane 35. Prior to this assembly, the handle half 33 can be elastically deformed in the region of the opening 26 to such an extent that the battery container can be inserted. The glueing of the two handle halves 33 and 34 along the line 35 cancels this elastically, so that the container 22 can no longer be readily extracted if the hand halves are not simultaneously disassembled.

Naturally, it is also possible to bevel the projections as indicated by the line 36 in Figure 7, so that the projections act, as it were, as barbs. In this case the battery container can be installed following the assembly of the handle 1 by forceful pressure, but cannot be fully extracted without the use of a suitable tool.

This embodiment of the invention ensures that when the test device is used to indicate a voltage, then in the event of any misactuation of the keying switch 5, and possibly a breakdown of the protective diode 19 which bridges this keying switch 5, two possible dangers are avoided, namely the touching of the contacts 20 and 21 or the possibility that due to the misinsertion of the battery into the cavity 23 the negative pole 6 of the battery 3 lies in the recess in such manner that it incorrectly touches the contact 21 and does not - as is correct - touch the contact 20. Naturally the touching of the contacts 20 and 21 by a user in the event of misactuation of the key 5 during the display of a voltage could be a serious and dangerous condition.

WHAT WE CLAIM IS: 1. An electrical circuit test device for detecting the presence and polarity of an electric voltage, and for conducting a continuity test, said device comprising two probes in the form of handles connected by a cable and provided with contact points, at least one of said handles serving as a housing for circuit components of the device, said components including two luminescence diodes connected in parallel with opposite polarities, which diodes are con nected to one contact point via a ceramic cold conductor thermister, and to the other contact point via a keying switch which normally establishes direct contact, but can be operated to bring into the series path the series combination of a battery source and a protective diode poled to conduct current from said battery when said contact points are conductively connected during a continuity test.

2. A test device as claimed in Claim 1, in which said keying switch is arranged between a guard ring surrounding its handle and the metal point of the handle.

3. A test device as claimed in Claim 1 or Claim 2, in which a Zener diode is connected in parallel to the keying switch.

4. A test device as claimed in any one of Claims 1 to 3, the circuit components of the device are accommodated in one said handle.

5. A test device as claimed in Claim 4 when dependant upon Claim 1 or upon Claim 3 when dependant upon Claim 1, in which said luminescent diodes are positioned between said guard ring and said contact point of said one housing, whilst said keying switch is mounted on the other side of said guard ring adjacent a recess in which a battery container holds a battery connected between contact springs, said battery container being releasably secured in its operating position by frictional engagement.

6. A test device as claimed in Claim 5, in which said ceramic cold conductor thermistor, and said protective diode are positioned in said housing to be accessible from the exterior when said battery container is removed.

7. A test device as claimed in Claim 5 or Claim 6, when dependant upon Claim 3, in which said Zener diode is accommodated in the housing to be accessible from the exterior when said battery container is removed.

8. A test device as claimed in any one of Claims 5 to 7, in which retaining means are provided which prevent said battery container being freely removed to expose the interior of the housing when opened to effect battery replacement.

9. A test device as claimed in Claim 8, in which said retaining means are projections on said housing which normally retain the battery container from being fully removed from said housing.

10. A test device as claimed in Claim 8 or Claim 9, in which said battery container contains a cylindrical cavity for the accommodation of the battery, one end of which has a restricted opening into which the positive battery terminal fits, the other end being equal in diameter to the diameter of the battery, and the length between the two ends being equal to the length of the battery body, the length of the opening in the hous

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. In place of the projections 27 it is also possible to provide a bead 28 which extends along the entire length of the container 22. Since, when the container 22 is in this limited state of extraction, in accordance with Figure 7, the opening 26 remains closed to prevent access to the interior, so that it is not normally possible to touch the contact 20 or the contact 21. The projections serve to lock the container 22 in the fully inserted state. It is most advantageous to install the container 22 into the handle 1 when this handle is itself assembled. The handle 1 in this embodiment consists of two halves 33 and 34, as indicated in Figure 5 and Figure 7, which are screwed together or firmly glued to one another in a plane 35. Prior to this assembly, the handle half 33 can be elastically deformed in the region of the opening 26 to such an extent that the battery container can be inserted. The glueing of the two handle halves 33 and 34 along the line 35 cancels this elastically, so that the container 22 can no longer be readily extracted if the hand halves are not simultaneously disassembled. Naturally, it is also possible to bevel the projections as indicated by the line 36 in Figure 7, so that the projections act, as it were, as barbs. In this case the battery container can be installed following the assembly of the handle 1 by forceful pressure, but cannot be fully extracted without the use of a suitable tool. This embodiment of the invention ensures that when the test device is used to indicate a voltage, then in the event of any misactuation of the keying switch 5, and possibly a breakdown of the protective diode 19 which bridges this keying switch 5, two possible dangers are avoided, namely the touching of the contacts 20 and 21 or the possibility that due to the misinsertion of the battery into the cavity 23 the negative pole 6 of the battery 3 lies in the recess in such manner that it incorrectly touches the contact 21 and does not - as is correct - touch the contact 20. Naturally the touching of the contacts 20 and 21 by a user in the event of misactuation of the key 5 during the display of a voltage could be a serious and dangerous condition. WHAT WE CLAIM IS:

1. An electrical circuit test device for detecting the presence and polarity of an electric voltage, and for conducting a continuity test, said device comprising two probes in the form of handles connected by a cable and provided with contact points, at least one of said handles serving as a housing for circuit components of the device, said components including two luminescence diodes connected in parallel with opposite polarities, which diodes are con nected to one contact point via a ceramic cold conductor thermister, and to the other contact point via a keying switch which normally establishes direct contact, but can be operated to bring into the series path the series combination of a battery source and a protective diode poled to conduct current from said battery when said contact points are conductively connected during a continuity test.

ing being substantially equal to the length of the battery container.

11. An electrical circuit test device substantially as described with reference to Figure 1, Figure 4 or Figures 5, 6 and 7.

12. An electrical circuit test device as claimed in Claim 11, having a circuit substantially as described with reference to Figure 2 or Figure 3.