GB2338310A

GB2338310A - Electrical test meter with audible and visual measurement indication means

Info

Publication number: GB2338310A
Application number: GB9910867A
Authority: GB
Inventors: David Peter Grant
Original assignee: ACT METERS Ltd
Current assignee: ACT METERS Ltd
Priority date: 1998-06-11
Filing date: 1999-05-12
Publication date: 1999-12-15
Also published as: GB9910867D0

Abstract

An electrical test meter 10 comprises means for measuring an electrical parameter, means 32 for displaying the measured parameter and means 16 for generating a tone corresponding to the measured parameter. The electrical parameter may relate to resistance or voltage. The display means 32 may be a needle/dial, LED or LCD. The tone generating means 16 may include an amplifier linked to a loudspeaker. The test meter may be part of a kit used in identifying faults in alarm systems. A method of testing an alarm system using the test meter is also disclosed.

Description

1 TITLE: Circuit Testing

DESCRIPTIO

2338310 This invention concerns electrical circuit testing.

Conventional test meters are used for testing electrical circuitry for faults by meg resistance, voltage or current between two points and comparing the measurement with that when the circuit is in good working order. The use of a test meter is fairly simple in domestic equipment, such as a television set. However, problems arise when testing alarm circuits that have alarm detectors, such as electrical contacts, passive IR detectors, pressure pads and the like situated mainly some distance from a control unit for the alarm circuit and often in separate rooms. A person on his own cannot test such alarm circuits with a conventional test meter, since another person is required to activate the alarm detectors, such as by breaking contacts, while the first person remains at the control panel to monitor the signal received and indicated by a test meter connected to the control unit.

The object of this invention is to provide a test meter that may be used by a single person to test electrical circuitry, such as alarm circuitry, wherein alarm detectors are remote from the circuitry testing place, namely the control unit for the circuit.

According to this invention there is provided an electrical circuit test meter having means for connection to an electrical circuit, means for selectively measuring an electrical parameter of the circuit, means for displaying the parameter 2 measurement and means for generating a tone corresponding to the parameter measurement.

Typically the parameter chosen for measurement will be electrical resistance. Preferably resistance variations down to 0.01 ohm may be measured by the test meter of the invention and such measurement variation indicated both by the display me= and by variation in pitch of the tone generated.

The test meter is ideally suited to testing alarm circuits. The meter may be connected to the control unit of the alarm circuit and switched on to produce a continuous tone of the same pitch. Then the various alarm detectors can be checked, to ensure that they are operating correctly. For example, electrical contacts can be tapped and provided they are m order there should be no change m the tone. If however, the tone changes when the contacts are tapped, that indicates there is a fault that needs rectifying.

The tone may be generated via a loudspeaker associated with, preferably within, the test meter body. The tone is preferably generated via an amplifier so that the volume can be adjusted, preferably through a range of 0 to 90 dB.

To enable the test meter to be moved from the circuit control unit nearer to a test location, which may be usefW for larger installations, an extension cable may be provided, typically of about 14 metres in length to connect between the test meter and the control unit.

Preferably the test meters of the invention will be arranged to test continuity, resistance and voltage over the ranges 0-20 ohms, 0-200 ohms, 0-2K, 0-20K, 0-200K and 0-200 vdc.

3 The display means of the test meter of the invention may be of any suitable type, such as a movable needle over a marked dial, a fight emitting diode display or preferably a liquid crystal display.

The test meter of the invention is preferably battery powered and preferably the batteries used are rechargeable.

The invention further comprehends an electrical circuit testing kit comprising a test meter of the invention powered by one or more rechargeable batteries, an extension cable and a battery charger. Preferably the testing kit of the invention is provided in a carrying case, ideally of briefcase type.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a test meter of the invention; Figure 2 is a circuit diagram of the test meter of Figure 1; and Figure 3 shows the test meter of Figures 1 and 2 in use.

Referring to the accompanying drawings, a test meter 10 suitable for use in testing electrical alarm circuits comprises a body 12, which may be made of sheet metal or of plastics material. The body 12 contains electronic circuitry (see Figure 2) for selective measurement of continuity, resistance and voltage. For selection of the parameter to be measured there is a selection knob 14 on the front of the test meter. Continuity, resistance and voltage ranges provided are 20 ohms, 200 ohms, 2K, 20K, 200K and 200 vdc.

The circuitry also includes means for generating a tone of variable pitch to be output via loudspeaker 16. A volume control knob 18 is provided on the front of the 4 test meter body.

Connection to an electrical circuit is via a co-axial connector 20 on the front of the test meter body, to which co-axial connector 22 having a first coaxial cable part 23 splitting to two leads 24, 26 each with a crocodile clip for gripping onto an electrical contact or wire are connected. An extension cable 28 wound on drum 30 may be interposed between the connectors 20 and 22, so that the test meter can be carried a distance away from a control unit of a circuit under test, typically a distance of about 14 metres.

The measurement taken is shown on liquid crystal display 32 on the front of the test meter body. An onloff switch 34 is also provided on the front of the test meter body. The test meter 10 is powered by rechargeable batteries. The batteries may be recharged in situ, for which a suitable battery charge may be provided.

The test meter 10 may be used in the following exemplary manner. The meter is connected to the control unit 51 of an electrical alarm circuit 50 under test across appropriate contacts thereof. The circuit shown has an electrical contact 52 that, for example, is made when a door or window is closed but broken when the door or window is opened. The test meter is switched on and resistance measurement selected. A continuous tone at a particular pitch is generated via the loudspeaker of the test meter. With the contact 52 closed, the contact can be tapped to ascertain if there is any change in the resistance measurement across the contact. Any change will be indicated by the display and more importantly by a change in the pitch of the tone. Any change indicates that the contact is faulty and needs repairing or replacing.

The test meter can be left at the control unit and the tone emitted used as an indication of any faults in the circuit or the meter may be connected to the control unit via the extension cable, so that the meter can be carried to each test site of the circuit as far as is possible.

6

Claims

CLAIMS 1. An electrical circuit test meter having means for connection to

an electrical circuit, means for selectively measuring an electrical parameter of the circuit, means for displaying the parameter measurement and means for generating a tone corresponding to the parameter measurement.
2. A test meter as claimed in claim 1, wherein the parameter chosen for measurement is electrical resistance.
3. A test meter as claimed in claim 2, wherein resistance variations down to 0. 0 1 ohm are measured and such measurement variation indicated both by the display means and by variation in pitch of the tone generated.
4. A test meter as claimed in claim 1, 2 or 3, wherein the tone is generated via a loudspeaker associated with the test meter body.
5. A test meter as claimed in claim 4, wherein the tone is generated via an amplifier so that the volume can be adjusted.
6. A test meter as claimed in claim 5, wherein the volume is adjustable through a ranae of 0 to 90 dB.
7. A test meter as claimed in any one of claims 1 to 6, having an extension cable for connection between the test meter and a remote location.
8. A test meter as claimed in any one of claims 1 to 7, arranged to test continuity, resistance and voltage over the ranges 0-20 ohms, 0-200 ohms, 0-2K, 020K, 0-20 OK

ZP and 0-200 vdc.
9. A test meter as claimed in any one of claims 1 to 8, wherein the display means is a movable needle over a marked dial, a light emitting diode display or a liquid crystal 7 display.
10. A test meter as claimed in any one of claims 1 to 9, wherein the test meter is battery powered,
11. A test meter as claimed in claim 10, wherein the batteries used are rechargeable.
12. An electrical circuit testing kit comprising a test meter as claimed in any one of claims 1 to 11 powered by one or more rechargeable batteries, an extension cable and a battery charger.
13. A method of testing an alarm circuit comprising connecting a test meter as claimed in any one of claims 1 to 12 to the control unit of an alarm circuit and switching on the meter to produce a continuous tone of the same pitch, and checking alarm detectors in turn to assess whether they are operating correctly by reference to changes in the tone produced by the test meter.
14. A test meter substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.