GB2331588A

GB2331588A - Electrical test device

Info

Publication number: GB2331588A
Application number: GB9723370A
Authority: GB
Inventors: Gavin Peter Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-11-06
Filing date: 1997-11-06
Publication date: 1999-05-26
Anticipated expiration: 2017-11-06
Also published as: GB2331588B; GB2331588A9; GB9723370D0

Abstract

An electrical test device comprises test connection terminals 11, 12, a switch 15 and first and second indicators 13, 14. The said device is arranged such that when the switch 15 completes a test circuit the first indicator 14 provides a signal when the resistance detected between the said terminals 11, 12 is equal to or less than a predetermined level and/or the second indicator 13 provides a signal when the resistance between the said terminals 11, 12 is equal to or greater than a predetermined level. The indicators 13, 14 may be different coloured light emitting diodes. The device may be used to test fuses. As an indication should be provided for a fuse whether it provides an open circuit or a short circuit, no fuse should be rejected as faulty merely due to the failure of the battery supply used within the device. If the battery fails neither of the indicators 13, 14 will operate.

Description

1 Electrical Test Device 2331588 This invention relates to an electrical

test device.

Electrical test devices are well known f or testing electrical equipment and supplies. One such electrical test device is the so-called multimeter, which is able to measure a. c and d. c. current and voltage as well as measure electrical resistance.

The most common requirement for an electrical test device in the home is for testing the continuity of mains fuses. However, multimeters are relatively expensive to buy just for this purpose and moreover multimeters can be difficult to set and read, unless the person is familiar with using a multimeter. Thus, it is common practice to replace and discard perfectly good fuses.

Continuity testers are known which emit a light or a sound when its two terminals are connected together, thereby indicating a short circuit. However, a disadvantage of continuity testers and multimeters is that it is often dif f icult to determine when an apparent open circuit is in f act attributable to a fault with the test device as opposed to an open circuit in the article being tested.

I have now devices and electrical test device which alleviates the abovementioned problem.

In accordance with this invention there is provided an electrical test device comprising a pair of terminals for connecting to the article to be tested, a test switch having a first state and a second state, low resistance indicator means arranged to provide a first signal when the switch is in the first state and to provide a second signal when the switch is in the second state and a resistance of less than a predetermined value is detected between the terminals, and high resistance indicator means arranged to provide a first signal when the switch is in the first state and to provide a second signal when the switch is in the second state and a resistance of more than a predetermined value is detected between the terminals.

In use, when testing fuses, the low resistance 1 2 indicator provides an indication that the fuse is good and the high resistance indicator provides an indicator that the fuse is f aulty. If no indication is provided, then it will be evident that the test device itself is faulty. 5 Preferably the indicator means are arranged to illuminate when the switch is in said second state and their respective appropriate resistances are detected between the terminals. Preferably the indicator means are arranged to illuminate in different colours so that they can be distinguished.

Preferably said predetermined resistance values are the same, both indicator means being arranged to illuminate if the detected resistance value is the same as said predetermined resistance.

Preferably the terminals are connected in series with said low resistance indicator means.

Preferably said high resistance indicator means comprises a pair of terminals, the high resistance indicator means being arranged to produce said second signal when a voltage above a predetermined value is connected across its terminals.

Preferably the high resistance indicator means is connected in parallel with said terminals; and most preferably in parallel with the series connection of the terminals and the low resistance indicator means. Preferably the high resistance indicator means comprises one or more diodes which determine the voltage at which said second signal is produced. 30 An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a plan view of an electrical test device in accordance with this invention for testing fuses; Figure 2 is an end view of the device of Figure 1; and Figure 3 is a schematic diagram of the device of Figure 1.

Referring to Figures 1 and 2 of the drawings, there is shown an electrical test device for testing fuses, comprising 3 a housing 10 and a pair of spaced apart C-shaped terminals 11, 12 disposed on the upper surface of the housing 10 for receiving respective ends of an elongate cylindrical fuse 20. Red and green light emitting diodes (LEDs) 13, 14 and a pushto-make switch 15 are also disposed on the upper surf ace of the housing 10.

A battery 16 and a printed circuit board 17 are housed inside the housing. The printed circuit board 17 comprises terminals that are connected via respective wires to terminals of the LEDs 13, 14 and switch 15, as well as to the C-shaped terminals 11, 12.

Ref rring to Figure 3 of the drawings, the positive terminal of the battery 16 is connected to the anode of the green LED 14 via the switch 15 and a series load resistor 19.

The cathode of the green LED 14 is connected to one of the Cshaped terminals 11. The other C-shaped terminal 12 is connected directly to the negative terminal of the battery 16.

The anode of the green LED 14 is also connected to the anode of the red LED 13. The cathode of the red LED is connected to the anode of the first of two series-connected diodes 18. The cathode of the second of the two diodes 18 is connected to the negative terminal of the battery 16.

In use, when a good fuse 20 is connected between the Cshaped terminals 11, 12 and the switch 15 is closed, current flows from the battery 16 through the resistor 19 and through the green LED 14 and the fuse 20, thereby illuminating the LED 14: the value of the resistor 19 is chosen such that about 1OmA flows through the LED 14.

Assuming that the resistance of the good fuse is negligible and assuming that a volt drop of 0.7 volts is developed across the forward biassed p-n junction of the green LED 14, it will be appreciated that the voltage between the anode of the red LED 13 and the cathode of the second seriesconnected diode is also 0.7 volts. 35 This low voltage is insufficient to drive the diodes 18 and red LED 13 into conduction and thus the red LED does not illuminate when a good fuse is connected between the terminals 11, 12. If an open circuit or high resistance fuse 20 is 4 connected between the terminals 11, 12 and the switch 15 is closed, then little or no current flows through the green LED 14. Thus, substantially the full battery voltage is applied between the anode of the red LED 13 and the cathode of the second of the series-connected diodes 18, thereby illuminating the red LED 13. A similar situation occurs when no fuse 20 is inserted.

It will be appreciated that a green light gives a positive indication that the fuse is good and a red light gives a positive indication that either no fuse is fitted or the fuse is faulty. If there are no lights, then this will either mean that the battery is exhausted or the test device is faulty. In this manner, spurious results and the wastage of good fuses can be avoided.

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Claims

1. An electrical test device comprising a pair of terminals f or connecting to an article to be tested, a test switch having a first state and a second state, a low resistance indicator arranged to provide a first signal when the switch is in the first state and to provide a second signal when the switch is in the second state and a resistance of less than a predetermined value is detected between the terminals, and a high resistance indicator arranged to provide a first signal when the switch is in the first state and to provide a second signal when the switch is in the second state and a resistance of more than a predetermined value is detected between the terminals.

2. An electrical test device as claimed in claim 1, in which the indicators are arranged to illuminate when the switch is in said second state and their respective appropriate resistances are detected between the terminals.

3. An electrical test device as claimed in claim 1 or claim 2, in which the indicators are arranged to illuminate in different colours.

4. An electrical test device as claimed in any preceding claim, in which said predetermined resistance values are the same, both indicators being arranged to illuminate if the detected resistance value is the same as said predetermined resistance value.

5. An electrical test device as claimed in any preceding claim, in which the terminals are connected in series with said low resistance indicator.

6. An electrical test device as claimed in any preceding claim, in which said high resistance indicator is in series with at least one diode for determining the resistance value at which said second signal is produced.

7. An electrical test device as claimed in claim 6, in which the series connection of the high resistance indicator and its associated diode or diodes is connected in parallel with the series connection of the terminals and the low resistance indicator.

8. An electrical test device substantially as hereinbefore described with reference to and as shown in the accompanying drawing.