GB2219408A - Electrical voltage tester - Google Patents

Abstract

In a voltage tester, an output signal from a voltage level and voltage polarity detecting circuit (3) is delivered via an optical coupling device (4) to a matrix circuit (5) which converts the signal into a binary address signal for a speech synthesizing section (6) to cause reproduction of a corresponding one of a set of stored spoken messages indicating the polarity and/or value of the sensed voltage. <IMAGE>

Description

Description of Invention "Electrical voltage tester" THIS INVENTION relates to an electrical voltage tester, particularly for testing the polarity and value of a voltage.

Known voltage testers comprise probes for contacting points in an electrical circuit whose polarity and voltage are to be tested, measurement circuitry for measuring the polarity and value of the voltage and visual indicating means to indicate the measured polarity and value.

In certain circumstances, when working with relatively high voltages, it can be hazardous for a user of such a tester to remove his eyes from the probes in order to consult the visual indicating means of the tester. There are also circumstances where it is difficult or impossible to look at or see the visual indicating means of the tester whilst applying the probes.

The present invention aims to provide a voltage tester which is safe and convenient to use in difficult circumstances and, to this end, there is provided a voltage tester comprising probe means for sensing a voltage to be tested, detecting means for detecting the polarity and/or value of the sensed voltage and delivering a corresponding electrical output signal, and audible signal generating means for generating in response to the output signal of the detecting means an audible signal selected from a set of audible signals identifying respective polarities and/or voltage values.

In order that the invention may be readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a polarity and voltage tester embodying the present invention; Figure 2 is a circuit diagram of the Figure 1 tester; Figure 3 is a logic table indicating the relationship between the inputs to a speech synthesizing section of the tester and an overall set of spoken messages generated by the speech synthesizing section; Figure 4 is a logic table indicating the relationship between the inputs to the speech synthesizing and a set of spoken polarity messages; and Figure 5 is a logic table indicating the relationship between the inputs to the speech synthesizing section and a set of spoken voltage value messages.

Referring firstly to the block diagram of Figure 1, a portable voltage tester embodying the invention comprises a pair of input leads 1 and 2 connected to probes for detecting an electrical voltage to be tested.

The polarity and value of the voltage between the two leads 1 and 2 is determined in a detecting circuit 3.

The detecting circuit 3 delivers on eight output lines 10 to 17 an output signal which depends upon the polarity and value of the voltage being tested.

The signals on the output lines 10 to 17 are applied via an optical coupling circuit 4 to corresponding input lines 20 to 27 of converting means in the form of a matrix circuit 5 which converts a signal on the input lines 20 to 27 to a corresponding binary signal on three binary address lines AO, Al and A2 as an input signal for an audible signal generator in the form of a speech synthesizing section 6 which stores eight predetermined spoken messages as shown in Figure 3 and has an audio output device 7, such as a loud speaker.

The detecting circuit has a reading detected output line 18 coupled to a start line 19 connected to the speech synthesizing board 6 via the optical coupling circuit 4, a start signal being applied to line 18 upon detection of a voltage across the lines 1 and 2 above a predetermined threshold.

The matrix circuit comprises a function switch 8 which places the tester in one of two modes, a first mode being for detection of the polarity of a test voltage and the other mode being for measurement of the value of the test voltage.

With the function switch in the polarity mode, a polarity signal received by the matrix circuit 5 from the detecting circuit 3 is converted into a corresponding address signal on the address lines AO to A2. The three possible polarity messages are indicated in Figure 4, together with an indication of the corresponding signals required on the address lines to identify each of the messages.

With the function switch in its value measuring position, a voltage value signal received by the matrix circuit 5 from the detecting circuit 3 is converted into a respective address signal on the address lines of the speech synthesizing section 6. The detecting circuit 3 detects whether a voltage under test attains any one of a set of five predetermined voltages, in the present case 12, 24, 50, 110 and 240 volts, and the resulting address signal identifies one of five corresponding voltage value messages stored at the corresponding address in the speech synthesizing section. The five possible voltage value messages are shown in Figure 5, together with their corresponding addresses.

Thus, in use of the tester, the function switch 8 may first be set to its polarity position, so that the polarity of a test voltage across lines 1 and 2 is communicated to the user of the tester as being either "positive", "negative" or "a/c" by reproduction through the device 7 of the corresponding stored message No. 2, 3 or 4 identified by the address signal emerging from the matrix circuit 5. Similarly, to measure the value of the test voltage, the function switch 8 is placed in its value measuring position, so that the address signal produced at the input to the speech synthesizing section 6 identifies that one of the stored voltage value messages Nos. 1 and 5 to 8 which corresponds to the value of the test voltage, such message being audibly reproduced through the device 7.

Figure 2 of the drawings illustrates one example of circuit 3 for implementing the various functions of the polarity and voltage tester illustrated in Figure 1. In Figure 2, elements corresponding to elements shown in Figure 1 are identified by the same reference numerals.

The circuit 3 of Figure 2 employs, as the optocoupling circuit 4, opto-isolating devices 4A, 4B and 4C.

Devices 4A and 4B each comprise four pairs of optically coupled light-emitting diodes and photosensitive transistors and the device 4C comprises a single lightemitting diode and photosensitive transistor pair.

A power supply for the speech synthesizing section 6 and the devices 4A, 4B is provided by a 9 volt battery 30 having its positive and negative terminals connected to respective positive and negative terminals 31 and 32 of the speech synthesizing section 6 via an on/off switch 33. A respective capacitor 34, 35, 36 is connected between each of the address lines AO, Al and A2 and the negative terminal 32. A light-emitting diode 37 is connected across terminals 31 and 32 to indicate an indication of the state of the switch 33.

In Figure 2, an input capacitor 40 of the detecting circuit 3 is connected across input lines 1 and 2. A first pair of diodes 41 and 42 in the device 4A are connected in series between the lines 1 and 2 for conducting current in one direction and a second pair of diodes 43 and 44 are connected in series between the lines 1 and 2 for conducting current in the other direction. The detector circuit 3 comprises a bridge rectifier circuit 45 for rectifying the input voltage and providing a rectified test voltage at its terminals 46 and 47. Terminal 46 is connected to one plate of a capacitor 48 and via a first indicator diode 49, first diode 50 of device 4B and a voltage divider to the other plate of capacitor 48. The voltage divider comprises resistors 51 to 55 connected in series, resistor 51 having a diode 38 connected in parallel therewith.

A resistor 56 connects the junction of diode 50 and the resistor/diode combination 51, 52 to the base of a first switching transistor 57 having its collector connected to the one plate of the capacitor 48 via a collector resistor 58. The emitter of transistor 57 is connected via a second diode 59 of device 4B, a second indicator diode 60 and a diode 61 to the emitter of a second switching transistor 62 having its base connected to the junction of resistors 51 and 52 and its collector connected to a line 63 containing diode 64 and connected to terminal 47 of rectifier 45. The junction of diodes 60 and 61 is connected via a third diode 65 of device 4B and a third indicator diode 66 to the emitter of a third switching transistor 67 having its base connected to the junction of resistors 52 and 53 and its collector connected to the line 63.The junction of the emitter of transistor 67 and the diode 66 is connected via a fourth diode 68 of device 4B and a fourth indicator diode 69 to the emitter of a fourth switching diode 70 having its base connected to the junction of resistors 53 and 54 and its collector connected to line 63. The junction of diode 69 and the emitter of transistor 70 is connected via the diode 71 of device 4c and a fifth indicator diode 72 to the emitter of a fifth switching transistor 73 having its base connected to the junction of resistors 54 and 55 and its collector connected to line 63. The junction of diode 72 and the emitter of transistor 73 is connected via a sixth indicator diode 74 to the emitter of a sixth switching transistor 75 having its base connected to the junction of resistor 55 and capacitor 48 and its collector connected to line 63.The junction of capacitor 48 and resistor 55 is also connected via resistor 76 to the base of a transistor 78 of a transistor pair comprising transistors 78 and 79, in which the emitter of transistor 78 is connected to the base of transistor 79 and the collectors of the two transistors are connected together and via a resistor 80 to the junction of diode 50 and resistor 51. The base of transistor 78 is connected to line 63 via resistor 77 and the emitter of transistor 79 is connected to the terminal 47 of rectifier 45 via resistors 81 and 82 and to the anode of diode 64 in line 63 via resistor 83.

Figure 2 illustrates the function switch 8 of the matrix circuit in the polarity mode. In this mode, the function switch connects the positive terminal 31 of the speech synthesizing section 6 to the collectors of two transistors 100 and 101 corresponding to the diodes 43 a nd 42 respectively of the device 4A. The function switch also connects the negative terminal 32 to the emitters of the transistors 102, 103 corresponding respectively to diodes 41 and 44 of device 4A.

In the value measuring mode, the function switch 8 connects the positive terminal 31 to the collectors of each of the transistors 104, 105 and 106 corresponding respectively to the diodes 59, 65 and 68 of the device 4B. In addition, the function switch 8 connects the negative terminal 32 to the emitter of the transistor 107 corresponding to the diode 50 of the device 4B.

A photosensitive transistor 108 of the device 4C has its emitter connected to the junction of diodes 61 and 65 and its collector connected to the junction of diodes 65 and 66, so that the transistor 108 is connected in parallel with the diode 65.

In operation of the device with the polarity switch 8 set in its polarity mode, the application across the input lines 1 and 2 of a test voltage having value of at least 6 volts and a positive polarity causes the diodes 43 and 44 to conduct, thereby rendering transistors 101 and 103 conducting, so that transistor 103 delivers a signal on line 19 to a start terminal 99 of section 6 and the transistor 100 delivers a signal on address line AO.

As can be seen from Figure 4 of the drawings, this results in message No. 2 being generated by the speech synthesizer section 6 and the user of the tester is audibly informed that the polarity of the test voltage is positive.

If the test voltage applied to lines 1 and 2 is at least 6 volts and negative, diodes 41 and 42 conduct and render corresponding transistors 102 and 101 conducting, so that transistor 102 delivers a start signal to terminal 99 and transistor 101 delivers a signal on address line Al, thereby generating the appropriate message No. 3 as indicated in Figure 4.

The application of an alternating voltage of at least 6 volts across input leads 1 and 2 results in all four diodes 41 to 44 conducting, with the result that transistors 102 and 103 deliver a start signal to terminal 99 and transistors 100 and 101 deliver signals to address lines AO and Al, thereby generating message No. 4 in Figure 4.

If the function switch 8 set in its voltage value measuring mode, the operation of the device is as follows: A rectified test voltage appears between terminals 46 and 47 of rectifier 45 and is applied across the voltage divider 51 to 55. Assuming that the test voltage has a level of at least 12 volts, current flows through diode 50 of device 4B, thereby activating transistor 107 to send a start signal to start terminal 99 of the speech synthesizer section 6. If the voltage does not attain 24 volts, then none of the diodes 59, 65, 68 and 71 conducts and no signal is sent from the corresponding transistors 104 to 107 on the address lines AO to A2. In these circumstances, as shown in Figure 5, the speech synthesizer 6 emits message No. 1 to audibly inform the user that the test voltage is 12 volts.If the test voltage attain 24 volts, then the second switching transistor 62 conducts, so that current also passes through diode 59 and activates transistor 104 in addition to transistor 107, so that the speech synthesizer receives both a start signal at terminal 99 and a signal on address line A2. Under these circumstances, the speech synthesizer generates the speech message No. 5 to indicate that the test voltage is 24 volts.

With a test voltage which attains 50 volts, the third switching transistor 67 conducts, so that current also flows through diode 65 and activates transistor 105 and the speech synthesizer consequently receives a start signal on terminal 99 and signals on both of address lines A2 and AO. As a result, the spoken message No. 6 is generated.

When the test voltage exceeds 110 volts, the fourth switching transistor 70 is brought into operation, with the result that diode 68 also conducts and transistor 106 is activated. The speech synthesizer then receives a start signal from transistor 107 and address signals from each of transistors 104 to 106 on three address lines and the spoken message No. 8 is generated to announce that 110 volts have been detected.

If a test voltage of 240 volt is received, the fifth switching transistor 73 comes into operation and diode 71 of device 4C conducts to activate its corresponding transistor 107 which acts to short circuit diode 65 and thus deactivates transistor 105 to remove the signal from address line AO and thereby cause message No.

7 to be generated to indicate that 240 volts are present.

The voltage corresponding to the spoken message is also visually indicated by diodes 49, 60, 66, 69 and 72.

In addition, if a test voltage reaching 415 volts is detected, the sixth switching transistor 75 is switched on to energise the further indicator diode 74 to indicate visually that this level of voltage has been detected.

Claims (11)

CLAIMS:

1. A voltage tester comprising probe means for sensing a voltage to be tested, detecting means for detecting the polarity and/or value of the sensed voltage and delivering a corresponding electrical output signal, and audible signal generating means for generating in response to the output signal of the detecting means an audible signal selected from a set of audible signals identifying respective polarities and/or voltage values.

2. A voltage tester according to claim 1, wherein digital audio signals defining the set of audible signals are stored at respective addressable locations in a memory of the audible signal generating means and converting means are provided for converting the output signal of the detecting means into an address signal identifying the location at which a corresponding digital audio signal is stored.

3. A voltage tester according to claim 2, comprising isolating means interposed between the detecting means and the converting means for electrically isolating the converting means from the detecting means.

4. A voltage tester according to claim 3, wherein the isolating means comprises a plurality of light-emitting elements receiving the output signal of the detecting means and transmitting the output signal to associated optically coupled photosensitive elements incorporated in the converting means.

5. A voltage tester according to claim 4, wherein the isolating means has a first group of light-emitting elements arranged to be selectively energised in dependence upon the polarity of the sensed voltage and a second group of light-emitting elements adapted to be selectively energised in dependence upon the value of the sensed voltage, selecting means being provided to select the output of the first group of elements or the output of the second group of elements for conversion by the converting means.

6. A voltage tester according to claim 5, wherein the selecting means comprises switch means incorporated in the converting means.

7. A voltage tester according to any one of claims 1 to 3, wherein the detecting means delivers a polarity signal representing the polarity of the sensed voltage and a voltage value signal representing the value of the sensed voltage, and selecting means are provided for selecting the polarity signal or the voltage value signal as the output signal of the detecting means.

8. A voltage tester according to any preceding claim, including means for generating a control signal indicating that a voltage above a predetermined level has been sensed for enabling the audible signal generating means.

9. A voltage tester according to any preceding claim, wherein the audible signal generating means comprises speech synthesizing means for reproducing a spoken message selected from a set of predetermined spoken messages.

10. A voltage tester substantially as hereinbefore described with reference to the accompanying drawings.

11. Any novel feature or combination of features described herein.