WO1989006365A1

WO1989006365A1 - Voltage indication apparatus

Info

Publication number: WO1989006365A1
Application number: PCT/AU1989/000001
Authority: WO
Inventors: Richard Woodcraft
Original assignee: Richard Woodcraft
Priority date: 1988-01-04
Filing date: 1989-01-03
Publication date: 1989-07-13
Also published as: AU2916989A; AU611760B2; GB2236193A; GB9019708D0

Abstract

Voltage indication apparatus (10) is disclosed including a first Light-Emitting Diodes (16) and a second Light-Emitting Diode (17) attached in parallel opposed relationship between a test probe (18) and a centre tap (13) on a voltage divider formed from a pair of resistors (11 and 12), the latter being terminated by alligator clips (14 and 15) which may be connected to the power rails of a circuit to be tested. During testing, current passes through and illuminates the first Light-Emitting Diode (16) if the test probe (18) is connected to a voltage between the voltage at the centre tap (13), which is typically half of the voltage between the power rails, and the voltage of the negative power rail. If the test probe (18) is connected to a voltage between the voltage at the centre tap (13) and the positive power rail, the second Light-Emitting Diode (17) will be illuminated. The apparatus is not polarised, and the alligator clips (14 and 15) may be connected to either power rail.

Description

VOLTAGE INDICATION APPARATUS

— BACKGROUND OF THB INVENTION — This invention relates to voltage indication apparatus. This invention has particular but not exclusive application to automotive electrical system voltage indication, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as digital electronic circuit voltage indication. Voltage indication or measurement is necessary for trouble shooting in electrical systems. This is usually carried out by connecting a voltmeter to test points within the system. Voltmeters are expensive and can be damaged easily. Frequently, most wires in wiring assemblies have only two possible voltage levels which are equal to the low and high voltage levels provided by the power supply. Typical examples of such systems are automotive electrical systems and many types of digital electronic circuits. In such systems, it is usually sufficient for the voltage indicating means to indicate whether a test point in the system is at the upper system voltage level, the lower system voltage level, or is not connected to either.

~ DESCRIPTION OF THB PRIOR ART — A light bulb fitted with probe-type leads is often used by mechanics as a voltage indicator. Such an indicator can indicate that a voltage difference exists between two test points, but is incapable of distinguishing between test points at the same voltage, and test points which are not connected to one another, as the light bulb will remain dark in both cases. In addition, such test lamps can damage the electronics of modern electrical systems by drawing excessive currents from them. They are also susceptible to damage by shock loads.

An indicating tool which is useful for determining the presence of voltages within a circuit is the "LOGIC PROBE", which is commonly used in digital electronic circuit testing. Logic probes, however, contain integrated circuit electronics which are relative expensive compared to passive components, and are easily damaged by voltage spikes such as may be present in the electrical system. For instance, automotive electrical systems typically include voltage spikes over 200 volts reflected from the ignition system. A logic probe for use in such an environment thus requires the further complication of protection circuitry to protect the integrated circuits. A further disadvantage of logic probes is that their power leads must be connected to the power rails of a circuit under test in the correct polarity, or damage to the probe may result. This shortcoming can only be alleviated by adding further components to^' the probe. The present invention aims to alleviate the above disadvantages and to provide voltage indication apparatus which will be reliable and efficient in use. Other objects and advantages of this invention will hereinafter become apparent. With the foregoing and other objects in view, this invention in one aspect resides broadly in voltage indication apparatus for testing in an electrical system, and including:- voltage division means ; circuit connectors connectible between a respective upper system voltage conductor and a lower system voltage conductor and said voltage division means whereby an intermediate voltage point may be produced in said voltage division means, and a pair of polarised indicating means connected in opposed polarity between said intermediate voltage point and a test probe. Preferably, the voltage division means is a pair of resistors connected in series as a voltage divider, although of course other voltage division means such as integrated circuits, zener diodes, or a resistor combined with a zener diode may be used if desired. Preferably the polarised indicating means are in the form of light emitting diodes (LED) whereby a selected one of the pair may be illuminated when a voltage of one polarity or the other is present across the polarised indicating means . Of course, if desired, other polarised indicating means such as polarity-sensitive buzzers, or incandescent lights in series with diodes, may be used. A tri-colour LED assembly, incorporating two LEDs in a parallel opposed-polarity configuration within a single component may be used if desired. Power supply indication means may be provided, connected between the upper system voltage terminal and the lower system voltage terminal whereby an indication of an applied voltage between the upper and lower system voltage terminals may be provided. The power supply indication means may include a LED, and the LED may be connected to the upper and lower system voltage levels through a bridge of diodes and a current limiting resistor, such that the LED will be supplied with current of the correct polarity regardless of the polarity of the voltage across the power supply indication means.

The voltage indication means may be adapted for operation with a power supply of a particular voltage level. If desired, however, the voltage indication means may include adjustable resistance means within the voltage divider or in series with the polarised indicating means whereby a selected current flow through the polarised indicating means may be maintained regardless of variations in the power supply voltage. In particular, voltage indication means may be provided having resistance values in the voltage divider which are variable by the operation of switching means between values suitable for operation with a twelve-volt power supply and values suitable for operation with a twenty- four-volt power supply.

In another aspect of this invention, voltage indication means is disclosed includin :- a single attachment clip connectible to a zero voltage level; a test probe connectible to an upper voltage level or to said zero voltage level; voltage indicating means connected between said attachment clip and said test probe, said voltage indicating means providing a visual or audible indication of the presence of a voltage of selected polarity between said attachment clip and said test probe; and conductivity indicating means connected between said attachment clip and said test probe and adapted for providing a visual or audible indication of the presence of circuit continuity between said attachment clip and said test probe. Preferably, the indicating means are in the form of

LEDs, and a battery is provided within the conductivity indicating means for supplying the current necessary to light the LED associated with the conductivity indicating means. Preferably also the voltage indicating means and the conductivity means each include a zener diode, such that circulation of current from the battery through the voltage indicating means is inhibited.

In a further aspect, this invention resides in voltage o indicating means including an analog-to-digital converter connectible to a circuit through clamping means to provide power for its operation and having a test probe connected to its input terminal, said analog-to-digital converter having a plurality of LEDs connected to its outputs, whereby voltages measured by said test probe may be converted to voltage range data, and whereby selected LEDs may be energised to indicate the voltage range of the voltage measured by said test probe. In a further aspect, this invention resides in a test probe assembly for testing an electrical system, and including: - a voltage indication means as defined in any one of the preceding claims ; an elongate housing enclosing said voltage indication means; a conductive member extending from one end of said elongate housing and connected to said test probe; mounting means in the end of said housing for mounting said polarised indicating means, and a flexible circuit connection attachable to the respective circuit connector and a system voltage conductor.

The test probe assembly may include mounting means for mounting power supply indication means .

— BRIEF DESCRIPTION OF THE DRAWINGS — In order that this invention may be more easily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention, wherein:-

FIG. 1 is a schematic diagram of a voltage indicating apparatus; FIG. 2 is a schematic diagram of a variation to the voltage indicating apparatus of FIG. 1;

FIG. 3 is a schematic diagram of a further variation to the voltage indicating apparatus of FIG. 1; FIG. 4 is a schematic diagram of an alternative embodiment of voltage indicating apparatus; FIG. 5 is yet another embodiment of voltage indicating apparatus , and FIG. 6 is a test probe assembly according to the invention.

— DESCRIPTION OF THE PREFERRED EMBODIMENTS — The voltage indicating apparatus 10 shown in FIG. 1 includes a pair of resistors 11 and 12 connected to a common junction 13, and with their free ends attached to alligator clips 14 and 15. The anode of a first light emitting diode (LED) 16 and the cathode of a second LED 17 are also attached to the common junction 13, while the cathode of the first LED 16 and the anode of the second LED 17 are both attached to a test probe 18. The circuitry is enclosed in a housing 19.

In the preferred embodiment, the apparatus 10 is adapted for use in twelve volt automotive electrical systems, and the resistors 11 and 12 are approximately equal in value.

In use, the alligator clips 14 and 15 are attached to the positive .and negative supply rails of the twelve volt electrical system, producing a voltage at the junction 13 six volts above the negative supply rail. It is not necessary to connect the alligator clips 14 and 15 to selected supply rails, as the desired voltage will be produced at the junction 13 with the alligator clips 14 and 15 in either possible orientation.

When the test probe 18 is not connected to the electrical system under test, the LEDs 16 and 17 have no voltage across them and thus do not light up. When the test probe 18 is connected to a point in the circuit under test which is between approximately eight and twelve volts potential, current flows through the second LED 17 and the resistor 11 or 12 connected to the zero volt supply rail, and it lights. It is preferred that the LED indicating a twelve volt rail be red.

When the test probe 18 is connected to a point in the circuit under test which is at zero potential, current flows through the first LED 16 and the resistor 11 or 12 connected to the twelve volt supply rail. It is preferred that the LED indicating a zero rail be green.

The voltage indicating apparatus 20 shown in FIG. 2 is similar in operation to the apparatus 10, but it includes further resistors 22 and 24 which are placed in series with resistors 21 and 23 respectively, and which may be shorted by respective poles of a voltage selection switch 23. The values of the resistors 21 and 23 are selected for operation on vehicles with twelve volt electrical systems , and the values of the resistors 22 and 24 are selected such that the respective series combinations of resistors 21 and 22 and 23 and 24 are suited for operation on vehicles with twenty-four volt electrical systems .

When it is desired to use the voltage indicating apparatus 20 on a vehicle with a twelve volt electrical system, the switch 23 is placed in the closed position, shorting out the resistors 22 and 24. When it is desired to use the apparatus 20 on a vehicle with a twenty-four volt electrical system, the switch 23 is opened, increasing the values of resistance between the junction 25 and the alligator clips 26 and 27 to values suitable for operation at the higher voltage.

The voltage indicating apparatus 40 shown in FIG. 3 is similar to the apparatus 10, with the addition of an indicating light, preferably yellow or amber, to indicate that the apparatus 40 is being correctly energised from the supply rails. The indicating light assembly 41 consists of a current-limiting resistor 42, a bridge of diodes 43 and a LED 44 connected within the diodes 43. The assembly 41 is connected between the alligator clips 45 and 46.

When the apparatus 40 is connected between a pair of supply rails, current passes through the resistor 42, the diodes 43 and the LED 44 , lighting the LED 44 to indicate that the apparatus 40 is powered. The diodes 43 route the current in the correct direction through the LED 44 regardless of the orientation of the alligator clips 45 and 46 relative to the supply rails. FIG. 5 shows a form of voltage indicating apparatus 50 which requires the connection of a single alligator clip 51 to either supply rail. Between the alligator clip 51 and the test probe 52 are two series assemblies of components placed in parallel. The positive indicating assembly 53 has the cathode of a red LED 54 connected to the alligator clip 51, while the anode of the LED 54 is connected to the anode of a six-volt zener diode 55. The cathode of the six-volt zener diode 55 is connected to the test probe 52 through a current- limiting resistor 56. The negative indicating assembly 57 is a series combination of a resistor 60, a six-volt zener diode 61, a green LED 62 and a twelve-volt battery 63. The zener diode 61 is oriented with its anode towards the test probe 52, while the green LED 62 has its anode towards the alligator clip 51. The battery 63 has its positive terminal oriented towards the test probe 52.

The voltage indicating apparatus 50 is prepared for use by connecting the alligator clip 51 to one of the supply rails , such as for instance the zero voltage rail. Current is prevented from flowing from the battery 63 through the circuit comprised by the positive indicating assembly 53 and the negative indicating assembly 57 by the sum of the zener voltages of the zener diodes 55 and 61 and the knee voltages of the LEDs 54 and 62, which is greater than the voltage of the battery 63.

When the test probe 52 is placed on a point at twelve volts potential, current flows through the positive indicating assembly 53 and lights the red LED 54. When the test probe 52 is placed on a point at zero potential, the ends of the negative indicating assembly 57 are effectively shorted, and the battery 63 drives current through the green LED 62. The voltage indicating apparatus 70 shown in FIG. 5 utilises an analog-to-digital converter 71 which is powered by connecting it to the positive and negative supply rails of the circuit under test by alligator clips 72 and 73. A test probe 74 is connected to the input of the converter 71, and a series of LED indicator lights 75 is connected to the digital outputs of the converter 71.

In use, the alligator clips 72 and 73 are connected to the positive and negative supply rails of the circuit under test, and the test probe 74 is placed on a point of unknown potential. The converter 71 measures the analog voltage on the test probe 74, and energises one or more of the lights 75 to indicate the level of voltage on the test probe 74 relative to the positive and negative supply rails.

Referring now to FIG. 6, it will be seen that the test probe assembly 80 includes a voltage indication apparatus 81 mounted within a housing 82 which terminates in a probe tip 83 which is connected to the test probe of the voltage indication apparatus 81. Power leads 84 extend from the voltage dividing αεans through the housing 82 and terminate in alligator clips 85 which may be attached to the power rails of a circuit under test. LEDs 86,. 87 and 90 are mounted on the rear face 91 of the housing 82.

In use, the alligator clips 84 are connected to the power rails of a circuit under test (in any polarity), and the power LED 85 (yellow) lights if the power rails are live.

When the probe tip 83 is touched to a point on the circuit which is near the lower rail voltage, the "low" voltage LED (green) lights. When the probe tip 83 is touched to a point on the circuit approaching the upper rail voltage, the "high" voltage LED (red) lights.

It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is defined in the appended claims .

Claims

— CLAIMS —

1. Voltage indication apparatus for testing in an electrical system, and including:- voltage division means; circuit connectors connectible between a respective upper system voltage conductor and a lower system voltage conductor and said voltage division means whereby an intermediate voltage point may be produced in said voltage division means, and a pair of polarised indicating means connected in opposed polarity between said intermediate voltage point and a test probe.

2. Voltage indication apparatus as defined in Claim 1, wherein said voltage division means includes a pair of resistors connected in series as a voltage divider.

3. Voltage indication apparatus as defined in Claim 1 or Claim 2, wherein said polarised indicating means include light emitting diodes (LED) whereby a selected one of said " pair may be illuminated when a voltage of one polarity or the other is present across said polarised indicating means.

4. Voltage indication apparatus as defined in any one of the preceding claims, wherein there is provided power supply indication means connected between said upper system voltage conductor and said lower system voltage conductor whereby an indication of an applied voltage between the upper and lower system voltage conductors may be provided.

5. Voltage indication apparatus as defined in Claim 4, wherein said power supply indication means includes a LED connected to said upper and said lower system voltage conductors through a bridge of diodes and a current limiting resistor.

6. Voltage indication apparatus as defined in any one of Claims 2 to 5 , wherein one or both of said resistors are adjustable for operation with power supplies of a differing voltage levels .

7. Voltage indication apparatus as defined in Claim 6 , wherein said resistors are switchable between values of resistance appropriate for operation with a twelve-volt power supply and values appropriate for operation with a twenty- four-volt power supply.

8. Voltage indication apparatus includin :- a circuit connector connectible to an electrical conductor; a test probe connectible to a further electrical conductor; voltage indicating means connected between said circuit connector and said test probe, said voltage indicating means providing a visual or audible indication of the presence of a voltage of selected polarity between said circuit connector and said test probe; and conductivity indicating means connected between said attachment clip and said test probe and adapted for providing a visual or audible indication of the presence of circuit continuity between said attachment clip and said test probe.

9. Voltage indication apparatus as defined in Claim 8, wherein said indicating means include LEDs.

10. Voltage indication apparatus as defined in Claim 9, wherein said conductivity indicating means includes a battery wired in series with a LED and current limiting means.

11. Voltage indication apparatus as defined in Claim 10, wherein said voltage indicating means and said conductivity means each include a series zener diode, such that circulation of current from said battery through said voltage indicating means is inhibited.

12. Voltage indicating means for testing in an electrical system, and including:- an analog-to-digital converter connectible to a circuit through conductive attachment means for providing power for its operation; a test probe connected to the input conductor of said analog- to-digital converter, and a plurality of LEDs connected to the binary outputs of said analog-to-digital converter, whereby voltages measured by said test probe may be converted to voltage range data, and whereby selected LEDs may be energised to indicate the voltage range of the voltage measured by said test probe.

13. A test probe assembly for testing an electrical system, and including;- a voltage indication means as defined in any one of the preceding claims ; an elongate housing enclosing said voltage indication means; a conductive member extending from one end of said elongate housing and connected to said test probe; mounting means in the end of said housing for mounting said polarised indicating means, and a flexible circuit connection attachable to the respective circuit connector and a system voltage conductor.

14. A test probe assembly as defined in Claim 12 or claim 4, wherein said mounting means includes a mounting for said power supply indication means .