GB2170914A

GB2170914A - Testing electrical continuity and detecting voltage sources

Info

Publication number: GB2170914A
Application number: GB08603008A
Authority: GB
Inventors: John Lazenby Macdonald
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-02-09
Filing date: 1986-02-06
Publication date: 1986-08-13
Also published as: GB8503368D0; GB8603008D0; HK55790A; GB2170914B

Abstract

A hand held device for testing electrical continuity and detecting voltage sources comprises a voltage source (2), an LED indicator (4) a transistor (1), a probe (8) and a contact terminal (6) connected and arranged as shown. In use, the probe (8) is applied to a circuit to be tested and the user's body closes the circuit between the circuit to be tested and the contact terminal (6), such that if the circuit to be tested comprises electrical continuity or a voltage source, a voltage is applied to the semiconductor control (1) which turns on causing illumination of the LED. <IMAGE>

Description

SPECIFICATION A-hand held device for use in both testing electrical continuity and detecting voltage sources The present invention relates to a hand held device for use in both-testing electrical conti nuity and detecting voltage sources.

It is known to test electrical continuity by connecting a voltage source in series with an indicator-device, such as a meter or light bu)b across the circuit to be tested. However, this type of device requires the use of two probes or leads connected -across the circuit to be tested- which makes it awkward to use.

A number of devices are known for detect ing voltage sources. A simple device which can be used to check for the presence of an A.C. voltage source comprises a neon indica tor connected on one sideto a probe which can be placed in contact with the suspected source of A.C. voltage and on the other side to an earthing contact which the user touches to complete the circuit. This device is very effective, but cannot be used to test for D.C..

voltage source. Of course, a voltmeter can be connected to measure both A.C. and D.C. vol tage sources, but where it is required simply to detect the presence of a voltage source a voltmeter is unnecessarily sophisticated and expensive. Moreover, a voltmeter must be connected across the voltage source which means two probes or leads are required with the attendant difficulties of connection.

It is an objector the present invention to provide a hand held device for use in both testing electrical continuity and detecting vol tage sources, which requires the use of only one probe to form a direct contact with the circuit to be tested.

According to the present invention there is provided a hand held device for use in both testing electrical continuity and detecting vol tage sources, comprising a voltage source, in dicator means connected to one side of the voltage source, a semiconductor switch con nected between the indicator means and the other side of the voltage source, which semi conductor switch is turned on by the applica tion of a voltage thereto, a contact terminal connected to the voltage source and adapted in use to be in contact with a user of the device-and a probe connected to the semicon ductor switch, wherein in use the probe is applied to a circuit to be tested and the users body closes the circuit between the circuit to be tested and the contact terminal such that if the circuit to be tested comprises electrical continuity or a voltage source a voltage is applied to the semiconductor switch which turns on causing the indicator means to turn on.

Preferably, the semiconductor switch com prises a transistor having high input impedance and high input sensitivity. Such a transistor may be a Darlington pair type transistor connected in common emitter mode.

Preferably, the indicator means comprises a light emitting diode.

Preferably, half wave rectifier means are connected between the probe circuit and the semiconductor switch to half wave rectify A.C. voltages applied thereto. In addition, a smoothing capacitor may be connected across the output side of the half wave rectifier circuit.

Preferably, a high value resistance is connected between the probe and the semiconductor switch to attenuate voltages applied thereto.

Preferably, the device comprises a housing to the exterior of which the contact terminal is mounted so as tc; freely make electrical contact with a user of the device when held and from an end of which the probe extends.

Preferably, a connection from the contact terminal mounted to the exterior of the housing to the interior of the casing is provided by patches of conductive Velcro, (RTM) one of which is connected to the contact terminal and another of which is mounted in the casing, the two being connected together through an aperture in the casing beneath the contact terminal.

Preferably, the voltage source comprises a battery.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 shows a circuit diagram of a device embodying the present invention; and Figure 2 shows a device embodying the present invention.

Referring to Fig. 1 there is shown a transistor 1 connected in common emitter mode across a 9 volt battery 2. Although not shown the transistor 1 is a Darlington pair type transistor which has high input impedance and high input sensitivity. A 470my resistor 3 and a light emitting diode (LED) 4 are connected in series between the collector 5 of the transistor 1 and the battery 2, and to the junction between the resistor 3 and LED 4 is connected a contact terminal 6. To the base 7 of the MPS AT13 transistor 1 is connected a series connected arrangement of a probe 8, resistor 9a, 96 and a diode 10. The diode 10 is connected with it's anode to the base 7 of the transistor 1 and as such ensures that only positive voltages are conducted to the base 7 of transistor 1.Each resistor 9a, 96 has a high value of the order 4.7 Megohms and serves to attenuate any voltages applied to the base 7 via the probe 8. Between the base 7 and the emitter 10 of the transistor 1 is connected a parallel connected arrangement of 0.033 nanoFarad capacitor 11 and a 10MQ resistor 12. The pur pose of the capacitor 11 and the resistor 12 is to smooth out A.C. -voltages applied to the base of-transistor 1 via the probe 8.

-The -transistor 1 acts as a semiconductor switch which conducts between the collector 5 and the emitter 10 when a voltage is ap plied'to the base 7. When the transistor 1 is turned on current flows in the LED 4 which in consequence lights up.

Referring to Fig. 2 the components of the circuit of Fig.'2 are connected to a circuit board 13 which is mounted in a housing 14.

The LED 4-is soldered directly onto the circuit board 13 and is mounted in a hole in the housing 14 so as to be easily visible when the device is in use. Being mounted within the housing 14 the LED 4 fixes the position of the circuit board 13 within the housing 14. The probe 8 is secured in a slot 15 in the front end of the housing 14 and extends forward therefrom so as to be easily applied to a ter minal of a circuit to be tested. The probe 8 is connected to the circuit board 13 by resistor 9, one end of which is soldered to the probe 8 and the other end of which is soldered to the circuit board 13. The contact terminal 6 is mounted to the exterior of the housing 14 in such a position that the hand of a user of the device can esily make electrical contact with it when the housing 14 is picked up.The con tact terminal 6 is connected to the circuit board 13 by means of two patches of con ductive Velcro-(RTM) 16, 17. Patch 16 is scured to the underside of the contact termi nal 6 through a hole 18 in the housing 14 and patch 1 7 is secured directly to the circuit board;13. When the LED 4 engages in the hole provided therefore in the housing 14 the two patches 16, 17 mate up and by pushing them together a releasably secure connection is provided.

The operation of-the device embodying the present invention to test for electrical conti nuity and to detect a voltage source will now be described.

In order to test for electrical continuity the device embodying the present invention is held by the user so as to make contact with the contact terminal 6 and the probe 8 is applied to one side of the circuit. The user then closes the circuit between the contact terminal 6 and the probe 8 with his body by touching the other side of the circuit to be tested from the probe 8. If the circuit is con tinuous a small current will flow from the bat tery 2 to the base 7 of transistor 1 which will turn on and the LED 4 will light up.The de vice embodying the present invention can be used to test electrical continuity in any situa tion where the user can apply the probe 8 to one end of the circuit and touch the other end of the circuit, however, it is particularly suited to testing-fuses, electric lights and wires which can- be held at one end in one hand whilst the probe 8 is applied using the other hand to the other end. It can also be used to check semi-conductor components and particularly diodes. In this respect the integrity of the device can be roughly assessed by checking that the DN junctions thereof conduct in one direction, but not the other.

The procedure for checking a voltage source is identical to that described above for checking electrical continuity in that the probe 8 is applied to one side of the voltage circuit and the other side of the voltage source is connected to the contact terminal 6 through the users body which contacts both the contact terminal 6 and the other side of the voltage source. Where a voltage source is present it causes a voltage to be applied to the base 7 of transistor 1 which turns on, causing the LED 4 to light up. Of course, where the voltage source to be checked is a D.C. voltage source, such as a battery, the probe 8 must be applied to the positive terminal thereof or the diode 10 will be reverse biased and will not conduct.Indeed, because of this the device provides a convenient means of checking the polarity of a voltage as only position voltages relative to the voltage on the contact terminal will cause the LED 4 to light up.

However, where the voltage source is an A.C.

voltage source the diode 10 conducts the positive going side of the waveform to the base 7. Moreover, a degree of smoothing is provided by capacitor 11 and resistor 12.

Where the voltage source to be checked is a battery this can most conveniently be done by holding the device embodying the present in one hand whilst touching the contact terminal 6 and touching- the probe 8 to the positive side of the battery. The user can then close the circuit by touching the negative terminal of the battery with his other hand. In the case of an A.C. voltage source this will usually be, or be derived from, the mains circuit and as such will be earthed to ground. - In this case there is no need for the user to touch the earth side of the circuit with his free hand as an effective earth will usually be provided through his feet.

The device embodying the present invention provides a highly effective, yet very simple to use means for use in both testing electrical continuity and checking A.C. and D.C. voltage sources. It is particularly useful for checking the electrics of a car as the body of the car provides a common ground which can be touched anywhere to complete the circuit.

This means the device can very quickly and simply check lights, ignition circuits etc. Moreover, the device embodying the present invention is very safe to use as the input impedance of the base circuit is very high, being of the order of Megohms, which means that even where the device is used to check A.C.

mains voltages the current through the user will be very low. A 10 Megohms resistor 12 may be selected from any suitable value in the range 4.7 to 10 Megohms.

Claims

1. A hand held device for use in both testing electrical continuity and detecting voltage sources, comprising a voltage source, indicator means connected to one side of the voltage source, a semiconductor switch connected between the indicator means and the other side of the voltage source, which semiconductor switch is turned on by the appiica- tion of a voltage thereto, a contact terminal connected to the voltage source and adapted in use to be in contact with a user of the device and a probe connected to the semiconductor switch, wherein in use the probe is applied to a circuit to be tested and the users body closes the circuit between the circuit to be tested and the contact terminal such that if the circuit to be tested comprises electrical continuity or a voltage source a voltage is applied to the semiconductor switch which turns on casing the indicator means to turn on.

2 A hand held device as claimed in claim 1 wherein the semiconductor switch comprises a transistor having high input impedance and high input sensitivity.

3. A hand held device as claimed in claim 2 wherein the transistor is a Darlington pair transistor connected in common emitter mode.

4. A hand held device as claimed in claim 1 wherein the indicator means comprises a light emitting diode.

5. A hand held device as claimed in Claim 1 wherein half wave rectifier means are connected between the probe circuit and the semiconductor switch to half wave rectify A.C. voltages applied thereto.

6. A hand held device as claimed in Claim 5 wherein a smoothing capacitor is connected across the output side of the half wave rectifier circuit.

7. A hand held device as claimed in Claim 1 wherein a high value resistance is connected between the probe and the semiconductor switch to attenuate voltages applied thereto.

8. A hand held device as claimed in Claim 1 wherein the device comprises a housing to the exterior of which the contact terminal is mounted so as to freely make electrical contact with a user of the device when held and from an end of which the probe extends.

9. A hand held device as claimed in Claim 1 wherein a connection from the contact terminal mounted to the exterior of the housing to the interior of the casing is provided by patches of conductive Velcro, (RTM) one of which is connected to the contact terminal and another of which is mounted in the casing, the two being connected together through an aperture in the casing beneath the contact terminal.

10. A hand held device as claimed in Claim 1 wherein the voltage source comprises a battery.