AU2003270983A1 - Portable electric appliance tester - Google Patents

Description

11689AU

ORIGINAL

Complete Specification Applicant: David George Lewis Title: Portable electric appliance tester Address for Service: LESICAR PERRIN, 49 Wright Street, Adelaide, South Australia 5000, Australia The following statement is a full description of this invention, including the best method of performing it known to me/us: A Portable Electric Appliance Tester The present invention relates to a portable electric appliance tester and in particular to a single unit capable of carrying out three separate tests, High Voltage, Low Voltage and Polarity/Continuity on various electrical items concurrently and in real time.

BACKGROUND OF THE INVENTION It is a requirement of Australian law, as in many other countries that electrical equipment passes a safety check Australian Standard 3760 (AS3760). Accordingly there have been developed portable electric appliance testers capable of displaying a Pass or Fail result in accordance with specific tests made to specific electrical items. Examples of testers that are currently being used as an Australian industry standard include the range of TRIO testers with analogue displays and the range of WAVECOM testers that incorporate digital displays. The TRIO testers test the insulation resistance, earth resistance, and electrical continuity of earthed (Class 1) appliances, double insulated (Class 2) appliances, as well as extension leads and EPOD's (power-boards) while WAVECOM have a range of single-test units. The abovementioned devices comply with the Australian Standard 3760 (AS3760) wherein Class 1 appliances and leads are tested so that earth resistance is below 1 Ohm and insulation resistance between active/neutral and earth is above 1 Mega-Ohm and Class 2 appliances so that the insulation resistance between active/neutral and any exposed metal is above 1 Mega-Ohm. Polarity testing is not currently required of AS3760.

One of the difficulties of existing units such as the TRIO tester mentioned above are that they are relatively large and heavy kg) units. Further they test each of the features (insulation resistance, earth resistance and electrical continuity) separately, store the result and then only at the end of the test sequence display a Pass or Fail answer. This method of testing requires isolating components in its circuitry such as timers and relays that add to the overall cost of the unit and are common contributors to unit breakdown.

These units also commonly include a 500V high voltage test but not a 250V test which means that, for example, when a power board that includes a common surge protector is tested, the surge protector breaks down due to the voltage exceeding its 270V limit and a false Fail result is indicated.

A further difficulty with existing units is that they typically require mains power to operate and are therefore not truly portable units.

There are currently no testers, to the best knowledge of the applicant, that perform the abovementioned tests concurrently and in real time.

It is therefore an object of the present invention to overcome at least some of the aforementioned problems or provide the public with a useful alternative.

It is a further object of the present invention to provide a portable electric appliance tester and a method of concurrently testing insulation resistance, earth resistance and electrical continuity.

SUMMARY OF THE INVENTION Therefore in one form of the invention there is proposed a portable electric testing apparatus including: an insulation resistance testing means; an earth resistance testing means; a continuity testing means; and a polarity testing means whereby said apparatus is configured so that each of said testing means is capable of functioning concurrently and in real time.

In a further form of the invention there is proposed an electrical testing apparatus for measuring insulation resistance, earth resistance and polarity in an extension lead having an active, neutral and an earth including: a first socket to which is electrically connected one end of said lead; a second socket to which is electrically connected the other end of said lead; an insulation circuit, earth resistance circuit and a polarity circuit electrically connected to said first and second sockets; a first battery means to provide power to said insulation circuit; a second battery means to provide power to said earth resistance circuit; a third battery means to provide power to said polarity circuit; said insulation circuit including a first analogue ammeter said circuit configured so that when the first ammeter is at full scale deflection it indicates to the user that there is a contact between the active and earth or neutral and earth wires of the lead; said earth resistance circuit including a second analogue ammeter said circuit configured so that when the second ammeter is at full scale deflection it indicates to the user that the earth of the lead is not continuous; said polarity circuit including a light that illuminates if the active or neutral wires of the lead have been crossed wherein a user is simultaneously provided with a reading of each of the three circuits.

In preference said first socket is a female socket and said second socket is a male socket.

In preference there is a third male socket of a different configuration to said second socket.

In preference said insulation circuit is adapted to operate at a voltage of some 500 Volts said voltage causing full-scale deflection of the first ammeter.

In preference said apparatus insulation circuit is further adapted to operate at a voltage of some 250 Volts that causes full scale deflection of the first ammeter, said apparatus including a voltage selection switch to change the operating voltage of the circuit to 250 Volts.

In preference said insulation circuit, earth resistance circuit and polarity circuit is powered by a rechargeable 6 Volt 1.2 Amp battery.

In preference said insulation circuit is powered by 9 Volt DC batteries.

In preference said earth resistance circuit is powered by at least 4.5 Volt DC batteries.

In preference said polarity circuit is powered by 3 Volt DC batteries.

In preference said apparatus includes a low battery warning for the insulation and earth resistance circuit batteries.

In preference said low battery warning is a light emitting diode.

In preference said insulation circuit batteries and earth resistance batteries are adapted to be rechargeable.

Preferably said apparatus further includes a voltage calibration means adapted to calibrate the first ammeter to half-scale deflection. This provides a visual indication to the user that the equipment is calibrated correctly.

In a further form of the invention there is proposed a portable electric appliance testing unit, said unit having a testing circuit able to perform three functions, said functions including an insulation resistance test, an earth resistance test and a polarity test, said circuit comprising: a dual centre-scale first analogue test meter reading resistance from 5 Megohms to 500 Kilo ohms and indicating a pass or fail for said insulation resistance test; a second analogue test meter reading resistance from 0 ohms to 2 ohms and indicating a pass or fail for said earth resistance test; and a light indicator able to perform three different indications for said electrical polarity test, i.e.

if polarity in a lead is correct, incorrect or if polarity doesn't exist.

In a still further form of the invention there is proposed an electrical testing apparatus for testing the electrical safety of an appliance by measuring insulation resistance and earth resistance in two separate circuits including: a first socket to which is electrically connected said appliance; said insulation circuit electrically connected to said first socket and including a first analogue ammeter said circuit configured so that when the first ammeter is at full deflection it indicates to the user that there is continuity between active and earth and the appliance is unsafe; said earth resistance circuit electrically connected to said first socket and including a probe and a second.analogue ammeter said circuit configured so that when the probe is connected with conductive elements on said appliance zero deflection of the second ammeter indicates that there is no current flowing to the probe and the appliance is unsafe.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate several implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings, Figure 1 is a perspective view of a portable electric appliance tester in accordance with a first embodiment of the present invention; Figure 2 is a perspective view of the portable electric appliance tester of Figure 1 in use, testing a toaster; Figure 3 is an interconnect diagram of the entire unit of Figure 1; Figure 4 is a detailed schematic of the current limiters for both the High and Low Voltage tests with reference to Figure 2; Figure 5 is a detailed schematic of the High Voltage testing circuit of the invention with reference to Figure 3; Figure 6 is a detailed schematic of the Metering circuits for both the High and Low Voltage tests with reference to Figure 3 and Figure Figure 7 is a detailed schematic of the constant current battery charger of the tester of Figure 1; Figure 8 is a detailed schematic of the low battery warning of the tester of Figure 1; Figure 9 is a perspective view of a portable electric appliance tester in accordance with a second embodiment of the present invention testing an extension lead; Figure 10 is a perspective view of the portable electric appliance tester of Figure 9 testing an electrical appliance; Figure 11 is a top view of the electric tester of Figure 9; Figure 12 is a detailed schematic of the High Voltage testing circuit and other circuitry associated with the electric tester of Figure 9; and Figure 13 is a detailed schematic of the Low Voltage testing circuit and other circuitry associated with the electric tester of Figure 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts.

A first embodiment of the present invention can be seen in Figures 1-8.

Figure 1 illustrates the portable electric appliance tester unit 2 housed in a box made up of two elongate horizontal flat surfaces 4 and 6, spaced apart by two elongate vertical side panels 8 and 10 and two elongate vertical end panels 12 and 14 which together make up the rigid rectangular unit 2. Bottom surface 6 is the surface placed on any horizontal surface 16, top surface 4 provides the display area and side 8 and 14 typically provide the input and output surfaces for the present invention. Each of these will now be explained in more detail.

Top surface 4 houses four indicators, a High Voltage (HV) analogue test meter 18 which provides an indication of insulation resistance, a Low Voltage (LV) analogue test meter which tests earth resistance, a red/green LED (light-emitting diode) 22 to indicate polarity, and a red LED 24 to indicate battery condition. It also houses a rocker switch 26 to turn the tester on and off and a 3-position rotary switch 28 capable of switching between a first position 29 set for the 250V voltage scale, a second position 30 set for the 500V voltage scale and a third position 31 to test on board calibration.

The HV meter 18 is mounted to surface 4 with nuts and studs (not shown). The surface of the meter is divided into two areas that may be painted in different colours to provide an easily visual indicator as to whether a test has passed or failed. Needle 32 pivotably moves to signal either a Pass 34(usually painted green) or a Fail 36 (usually painted red) on either side of two centre scales for the 500V and 250V tests. The LV meter spaced apart from meter 18 and mounted in the same way to surface 4, consists of the same pivotable movement of a needle 42, however in this test to indicate a Pass or Fail on either side of only one centre scale. The other abovementioned features, namely LED 24 and switches 26 and 28 should be well known to those skilled in the art.

Located on end panel 14 is a male 3-pin plug end 48 to plug in a test appliance (not shown) or the female end 49 of a test lead 50, and a male IEC plug end 52 with built in 400 mA 240V rated HRC fuse to plug in an IEC lead (not shown).

Located on side panel 8 is a female 3-pin socket 54 to which, for example, a power board (not shown) can be plugged into, or the male end 53 of test lead 50. Also located on side panel 8 is a fixed connector 56 to which a test probe 58 (shown in Figure 2) is connected for ease of use of the probe. A 3 mm female mono-jack 60 is provided for the attachment of a battery charger (not shown).

Figure 2 illustrates the portable electric appliance tester 2 of Figure 1 performing a set of three tests on an electric appliance 3. The electric appliance lead 5 connects to unit 2 via its male plug 7 inserted into the female 3-pin socket 54. A test probe 58 connected to connector 56 is designed to be electrically connected to each metal part of the appliance 3, in this case a toaster, indicators 18, 20 and 22 providing the visual information to the user as to whether the appliance is safe.

With respect to the first embodiment of the present invention, rather than referring to each Figure 3-8 separately, an explanation of the circuitry involved in each of the three separate tests will be made whilst referring to the Figures.

The HV test (Test 1 Insulation Resistance) will be the first test explained.

Referring now to Figure 3, an appliance to be tested is plugged into female AC socket 54.

When the ON-OFF switch 26 is selected to the ON position, switch 64 is simultaneously pressed and allows a voltage of 8.4V from batteries 66 to flow to a current regulator 68 in the 500 VOLT GENERATOR PCB 70 through SWla connecting Figures 3 and 4. Current regulator 68 consists of a voltage regulator chip 72 with a variable resistor 74 connected, so that the output of the current regulator 68 is a nominal +9V at a current restricted to 1 mA.

This gives excellent regulation due to the absence of a voltage drop across a current limiting resistor used in existing units. This nominal voltage is now carried through to various points 76a, 76b, 76c, 76d, 76e, 76f and 76g in the 500/250 Volt Generator 78 in Figure 5, a detailed schematic of the circuitry in the voltage generator.

The volt generator 78 converts 9 V DC to a 9 V AC current that is centre tapped to produce a peak-to-peak voltage of some 18 Volts. Such voltage generators are well known in the art and use a standard multivibrator chip 80 for converting incoming 9V DC current.

Thus NAND gate IC1C works like an inverter in that it is configured as a CMOS square wave oscillator, i.e. pin 8 is tied to the 9V rail which is high. Initially, pin 9 is low and capacitor C1 is discharged which means that pin 10 is high. C1 will now be charged through R1 and when the voltage on pin 9 reaches the upper threshold level of the Schmitt input, the output will change state.

Two out of phase signals are fed to NAND gates IC1A and ICIB that act like inverters so that after the filter stage 82, Q1 and Q2 in area 84 are driven alternatively so that 9V is applied to each half of a transformer primary 86. The transformer steps up the primary voltage of 18V to about 125V. Next comes the voltage quadrupler 88 consisting of D1-D4 and C5-C8. This gives 250V and 500V for the two settings, provided that the inverter runs continuously.

To regulate this voltage up to 500 V, there is a feedback line 90 to the multivibrator chip 80 which consists of five resistors R8, R9, RI0, R11 and R12 in series to divide down the voltage. This voltage is compared to a reference voltage at amplifier 1C2 formed by R6, RV1, R7, ZD1 and C9.

The voltage can be set to be either 250V or 500V through rotary switch 28 in Figure 1, which corresponds to circuit switch 28 in Figure 5. This voltage then flows to the metering circuit of Figure 6. Of course the voltage selected can be varied to satisfy the particular local operating conditions.

Referring now to the metering circuit 100 in Figure 6 for which the input is 'From 500 Volt Generator'. The 250/500V from the volt generator of Figure 4 is fed directly with no current limitation to a test load (female socket 54 in Figure 3) in series with a meter 18 of 1 mA full-scale movement. That is, with a supply voltage of 500V and a test resistance of 1M ohm, the test current is 500 mA which is centre scale on the meter and with a supply voltage of 250V and a test resistance of 1M ohm, the test current is 250 mA which is 25% of the full scale of the meter.

The skilled addressee would now appreciate that with a simple visual test on the meter, a user is provided with an instant and easy to understand condition of the lead that is being tested.

Referring now to Figure 3 once again, the LV test (Test 2 Earth Resistance) will now be explained. A male AC plug 48 has its neutral and active pins connected in association with batteries 106 and fuse 108 while male IEC plug 110 has its neutral and active pins connected in association with batteries 112 and fuse 114. When the ON-OFF switch 26 is pressed to the ON position, a voltage of 4.8V from the Test 2 batteries 116 flows to the constant current regulator 118 in the 500V GENERATOR PCB through SWlb which connects Figures 3 and 4. The current regulator 118 consists of a voltage regulator chip 120 with a variable resistor 122 connected to output a current of 300mA. This is then fed directly to the test load (neutral pin of male plug 48 or IEC plug 52 or probe 58 in Figure 3) through the metering circuit 126 in Figure 6.

It can be seen in Figure 6 that the voltage drop across the test load is measured to give the resistance of the earth wire giving 50 micro amps full-scale movement of the meter 20. A test resistance of 1 Ohm at centre scale is set by the connection of a standard diode 130 across the meter 20 that gives a voltage of 600 mV regardless of the supply voltage. A variable resistor is also included before the diode to protect it from over-current.

Therefore, probe 58 is capable of measuring both 1 ohm and 1 MOhm resistance at the same time. This is possible because once the 500V output from the voltage generator reaches the Class 2 appliance being tested, and earth leakage is observed on the LV meter, the user then places the probe on each of the metal parts of the appliance. A current flows to the LV meter but because it is already at full-scale deflection, it bypasses it and continues to the HV meter that in turn displays an insulation resistance reading.

Although it is not shown in Figure 5, it is to be understood that switch 28 also comprises a third calibration position which passes a constant 500V through the on board 1 MOhm test resistor for the HV test to simulate an earth fault of 1 MOhm and for the LV test, it passes a constant 300 mA current through the on board 1 Ohm test resistor which simulates an earth continuity of 1 Ohm.

The circuitry for the continuity/polarity test (Test 3) is illustrated in Figure 3. The Test 3 batteries 106 and 112 for the male AC and IEC plugs 48 and 52 respectively, produce 3V DC across the active/neutral pins of both. A red/green indicating LED 22 is connected across the active/neutral pins of the female plug base 54. When a lead 50 is plugged into either of lEC male top 52 or male AC top 48 and female base 54, current passes through the lead in the direction of the connections. If the connection is correct, the LED 22 will light green, if the connection is incorrect, the LED 22 will light red and if there is no continuity, the LED 22 will not light.

A battery charger 134 is used to charge batteries 66 and 116 used in test 1 and test 2 respectively. The circuitry of the charger 134 can be seen in Figure 3 and Figure 7. Figure 3 shows how the charger 134 is connected to batteries 66 and 116 while Figure 7 shows the circuitry of the charger 134 itself. It can be seen that the batteries 66 and 116 are charged in parallel with current regulators, i.e. the use of LM317T voltage regulator chips modified with resistors for each battery supply. The HV test requires approximately a 9V battery supply, the LV test requires greater than 4.5V and less than 9V for safety, while the polarity/continuity test requires a 3V supply.

The portable electric appliance tester 2 also consists of a low battery warning 136 and the circuitry for this can be seen in Figure 3 and more clearly in Figure 8. Figure 3 illustrates how voltage from the batteries 66 and 116 are connected to the low battery detector 136 when the ON/OFF switches 26 and 64 are pressed. It can be seen in Figure 8 that when one of the batteries 66 or 116 is low, a red flashing LED 22 will light. As mentioned, both batteries 66 and 116 are charged in parallel and this is the reason that only one alarm circuit 136 is used.

A second embodiment of the present invention is illustrated in Figures 9-11. More specifically, Figure 9 illustrates the tester 138 testing an electrical extension lead 139, Figure illustrates the tester 138 testing an electrical appliance which in this case is once again a toaster 141, Figure 11 illustrating a general top view of the tester 138 and Figures 12-13 illustrating the detailed circuitry associated with the tester 138.

It is to be understood that the main feature of the present invention is common in both embodiments, that is, that the portable electric appliance tester is capable of carrying out the three abovementioned tests concurrently and in real time. This embodiment involves the use of an alternative power source and some other additional features that will each be clarified.

It is to be understood that some reference numbers referring to features on the unit 138 are also present on the circuit diagrams indicating the same component. For example, LED 158 can be seen in both Figure 11 and Figure 12. As the electrical components used in the tester are well known to those skilled in the art, they will only be generally referred to and their specific circuitry not discussed.

The tester 138 includes a housing 140 whereby the fittings of the unit are mechanically protected in a recessed surface 142 of the housing 140. One of these fittings is the ON/OFF switch 144. Once again, housed on the side walls of the tester are a male 3-pin plug 145 to plug in a test appliance, a male IEC plug 147 and female AC socket 149.

The tester 138 is preferably powered by a single 6V rechargeable gel cell battery as opposed to a greater number of non-rechargeable batteries as in the first embodiment.

There are a number of additions associated with the tester 138 of the second embodiment which will become evident. The tester 138 includes a banana plug or external test lead socket 146, a 'Check Function' test LED 148 (also shown in the function indicator switching circuit 150 of Figure 11) which indicates when either rotary switch 152 or 154 is in a position other than the normal 500V test mode, a lead polarity red/green LED 156 which indicates correct or incorrect polarity, or remains unlit if no lead is plugged into the tester or the lead has no continuity between active and neutral pins, and a high voltage check LED 158 which is connected to a tertiary winding in the high voltage transformer 160 (as seen in Fig 12) and proves that the high voltage is functioning correctly at the time of the test. Surface 142 also houses probe cord 161 which connects to a probe 163.

The tester 138 includes 3-position switch 152 switchable between a first position 162, second position 164 and third position 166. The first position 162 indicated by '240V or ext continuity' is chosen when testing for continuity in any equipment using external leads (not shown) inserted into banana plug 146, or when testing on 240V whereby the active/neutral pins are internally shorted (any test that can be done on 500V can be done on 240V). This setting is optimum when testing surge protected or delicate electronic equipment. The second position 164 indicated by '500V' is chosen at normal 500V test mode whereby the active/neutral pins are internally shorted so 500V is never put through the appliance. The third position 166 indicated by 'Continuity or Ext Earth' would be selected when testing continuity of the 240V circuit of the tested appliance or the earth resistance of any appliance using the external lead (not shown).

A second 3-position switch 154 is located adjacent and below switch 152. The switch is also switchable between a first position 168, a second position 170 and a third position 172.

The first position 168 indicated by 'Calibration' is selected when one wishes to internally check to prove the meter is reading accurately. A well calibrated tester will have both meters at centre scale when switched to this position. The second position 170 indicated by 'Test' is the required position to carry out any of the abovementioned tests. The third position 172 indicated by 'Battery Check' is selected when checking for battery power. At full scale deflection, the battery is fully charged while at scale deflection, the internal protection will shut the tester down to protect against inaccurate readings.

The selection criteria of each switch will later become apparent.

As should now be obvious, the tester 138 includes two meters 174 and 176 as per the first embodiment.

The upper meter 174 indicates the insulation resistance having an associated scale from approximately 5MOhm to 500KOhm and centre scale being 1MOhm (the fail mark) as described previously. The upper meter 174 further indicates the 240V circuit continuity of an appliance under test whereby full scale deflection indicates that there is a continuous electrical path through the appliance.

The lower meter 176 indicates the earth resistance of the appliance under test having an associated scale from 0 Ohm to 2 Ohm and centre scale being 1 Ohm (the fail mark) as described previously. The lower meter 176 further indicates the battery charge when this function is selected on rotary switch 154. It is envisaged that a separate battery scale will be located on the face of the tester 138.

Referring now specifically to the circuit diagrams of Figures 12-13. The voltage generator arrangement in this embodiment is quite different to that of the first embodiment.

The voltage generator includes oscillator and drive circuitry 178 as compared with a multivibrator 80. The oscillator and drive circuitry 178 includes a 555 timer 180 capable of producing very accurate time delays or oscillations. The oscillations are controlled by the oscillator control circuitry 182 which is fed by the voltage set and monitor circuitry 184. As can be seen, a current limiter 186 now sits in the voltage generator. A voltage doubler 188 replaces the voltage quadrupler and the voltage select circuitry 190 is found on the lower side of the divider as it is easier to monitor in this position. The insulation test meter circuitry 192 functions in substantially the same way as that previously described, as does the polarity indicator circuitry 194.

The Low Ohm test is not significantly different to that of the first embodiment and will therefore not be described in any great detail. A test current of 100 OmA is preferably used in order to reduce heat dissipation. The constant current source and low ohms tester circuit 196 together with the low ohm test meter circuit 198 can be seen in Figure 12. A battery check circuit 200 is a major addition to the circuit and the low voltage cutout circuitry 202 complements the addition. The battery check tests the voltage on the battery and if the voltage is below a pre-determined level, the tester will cease to operate due to the configuration of the low voltage cutout circuitry 202.

The polarity test source and mains alarm circuitry 204 includes another addition to the tester of the second embodiment, the addition being that ofpiezo buzzers or alarms 206 and 208 which are powered by their own batteries 210 and 212 respectively. These are very important in that if someone were to plug a live socket into one of the male plugs 145 or 147, an audible alarm will sound.

Finally, Figure 12 illustrates the battery charger and power supply circuitry 214. In the first embodiment, although not shown, the battery charger did not form part of the tester unit. Circuitry 214 is here included inside the tester 138.

The following paragraphs detail the procedure in which different tests should be undertaken for different equipment. Although the second embodiment includes additional features to the first embodiment, the general outcome of the tests is the same.

1) Class 1 Equipment (Continuity, Insulation Resistance and Earth Resistance) In the case of class 1 appliances, one would simply insert the male plug of the appliance into the female socket 149 of the tester 138. Continuity may be tested to ensure that all of the electrical circuit is tested. Rotary switch 152 is to be set to 'continuity or ext earth' and when the tester is switched on, full scale deflection of the top meter 174 indicates correct continuity.

In relation to insulation resistance, a user will return switch 152 to '500V' and an immediate indication of any insulation resistance fault between active or neutral and earth will be given on the top meter by a pass (green) or fail (red).

Finally, in relation to earth resistance, leaving switch 500V, the user is required to touch the probe 163 to each exposed metal section of the appliance. An immediate indication of earth resistance will be given on the bottom meter by a pass (green) or fail (red).

2) Class 2 Equipment (Continuity and Insulation Resistance) In the case of class 2 appliances, one would simply insert the male plug of the appliance into the female socket 149 of the tester 138. Continuity is once again tested to ensure all of the electrical circuit is tested. Rotary switch 152 is set to 'continuity or ext earth' and when the tester is switched on, full scale deflection of the top meter 174 indicates correct continuity.

In relation to insulation resistance, a user will return switch 152 to '500V' and touch the probe 163 to each exposed metal section of the appliance. An immediate indication of any insulation fault will be given on the top meter by a pass (green) or fail (red).

3) Extension Leads (Insulation Resistance, Earth Resistance and Polarity) In the case of extension leads, one would simply plug both ends of the lead into the appropriate receptacles of the tester 138 as previously described. An immediate indication of any insulation resistance fault between active or neutral and earth will be given on the top meter by a pass (green) or fail (red).

In relation to earth resistance, an immediate indication is given on the bottom meter by a pass (green) or fail (red).

In relation to polarity, an immediate indication is given on the red/green LED 156 labelled 'polarity' on the tester 138. As already mentioned, if the polarity is correct, the LED will light green and if it is wrong, the LED will light red. With no continuity of the active and neutral or no lead plugged in, the LED will not light.

4) Using External Leads (Continuity, Insulation Resistance and Earth Resistance) When using an external lead plugged into banana socket 146, one would first select '240V and ext continuity' on switch 152 and clip the lead to the active pin of an appliance and hold the probe to the neutral pin (or vice versa). Full scale deflection of the top meter 174 indicates correct continuity.

In relation to insulation resistance, a user will return switch 152 to '500V', clip the lead to both active and neutral pins and touch the probe to each piece of exposed metal. An immediate indication of any insulation resistance fault between active or neutral and earth will be given on the top meter 174 by a pass (green) or fail (red).

Finally, in relation to earth resistance, a user will change the position of switch 152 to 'continuity or ext earth', clip the lead to the earth pin and touch the probe to each exposed piece of metal. An immediate indication of earth resistance will be given on the bottom meter 176 by a pass (green) or fail (red).

It should now be apparent to those skilled in the art that the present invention provides for a unique portable tester that can measure the behaviour of a number of elements of a class 1/class 2 appliance, electrical lead or other electrical component simultaneously and provide an immediate result of the test. The tester can also be used with a probe to determine the safety of electrical appliances such as toasters, hair dryers etc.

In contrast to existing testers, where the tests are performed in series and the user is only provided with an indication if all of the tests have passed, the present apparatus provides an indication to the user as to what the fault, if any, may be. This is of commercial advantage to the user of the tester which is also able to accommodate country specific requirements.

Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognised that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

It is to be understood that in the context of this document, the phrases electrical resistivity and electrical continuity are one and the same thing.

In any claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.

Dated this Friday, December 19, 2003 Easytest Pty Ltd By his Patent Attorneys LESICAR PERRIN