GB2506708A

GB2506708A - Method for testing the integrity of electronic equipment

Info

Publication number: GB2506708A
Application number: GB1307895.1A
Authority: GB
Inventors: Michael Paul Threlfall
Original assignee: MK TEST SYSTEMS
Current assignee: MK TEST SYSTEMS
Priority date: 2013-05-01
Filing date: 2013-05-01
Publication date: 2014-04-09
Anticipated expiration: 2033-05-01
Also published as: GB201307895D0; GB2506708B

Abstract

A computer-implemented method for testing the integrity of electronic equipment for degradation or deterioration comprises taking a first measurement of the electrical resistance of a component and storing this value in memory or a database. A second measurement of the electrical resistance of the same or another component, which can be an identical component in an identical or other system, is taken and this value also saved. The two recorded values are compared with a difference or variance between the values calculated and if this difference exceeds a threshold, an indication is given to a user that the set limit has been breached. This method is particularly applicable to testing the continuity resistance and the insulation resistance, through measurements of the leakage current, of components of an aircraft.

Description

METHOD FOR TESTING EOUIPMENT

Technical Field of the Invention

This invention relates to testing equipment.

Background to the Invention

When manufacturing or building systems which include multiple electrical components and connections, it is important to test the components and connections during manufacture and/or immediately after manufacture of the system to ensure that the components function as they are intended to, and that components are connected to one another as intended.

An example of such a system is an aircraft, which includes a large number of components and connections between those components. It is important to ensure that all of the connections are complete and that, where a cable or component needs to be insulated from another cable or component, the required insulation is in place.

Currently, it is known to manually test electrical connectivity between components, and electrical conductivity and/or insulation of components themselves, in a newly-manufactured system, such as an aircraft. Such testing is typically carried out before the components and connections therebetween are secured in a housing of the system in which they are installed.

In order to retest components in an aircraft after manufacture, it is presently necessary to remove all components and connections from the aircraft, which is vety costly. Therefore, instead of retesting equipment after manufacture, high safety standards are put in place, and each component and wire is allocated a life expectancy beyond which it is not used and may be replaced.

Summary of Invention

According to a first aspect, the present invention provides a computer-implemented method for testing equipment, the method comprising: measuring a first electrical resistance of a component; storing a value for the first measured electrical resistance in a database; measuring a second electrical resistance of a component; storing a value for the second measured electrical resistance in a database; comparing the first electrical resistance value with the second electrical resistance value; calculating a variance of the first and second measured electrical resistance values; determining whether the variance exceeds a first threshold; and indicating to a user whether or not the variance exceeds the first threshold.

The first measured electrical resistance and the second measured electrical resistance may be stored in the same database. The component may be a component of an aircraft.

The component may be in a system, which may be an aircraft. The first electrical resistance may be measured at a first time, and the second electrical resistance may be measured at a second, later time.

The component of which the first electrical resistance is measured may comprise a component of a first system and the component of which the second electrical resistance is measured may comprise a component of a second system. The component of the second system may be equivalent to the component of the first system. The first system and the second system may be aircraft.

The method may further comprise allocating a unique identifier to each component.

The component of the first system may be one of a first plurality of components, and the component of the second system may be one of a second plurality of components. The measuring may comprise measuring an electrical resistance for each component of the first and second plurality of components.

The indicating may comprise displaying a first indication to a user if the variance is below the first threshold, displaying a second indication to the user if the variance is between the first threshold and a second threshold, and displaying a third indication to the user if the variance exceeds the second threshold. The first indication may be a first colour, the second indication may be a second colour and the third indication may be a third colour.

The measuring of electrical resistance may comprise applying a fixed current to the component, measuring the voltage across the component, and dividing the measured voltage by the applied current.

The method may be a method for testing continuity resistance of the component. The fixed current may be supplied by a low voltage power supply. The measuring of electrical resistance may comprise applying a fixed voltage across two electrical components, measuring a leakage cunent flowing between the electrical components, and dividing the applied voltage by the measured current.

The method may be a method for testing the insulation resistance of the component. The fixed voltage may be supplied by a high voltage power supply.

Thc method may further comprise storing for each component a component identifier associated with the measured electrical resistance value. The method may further comprise storing for each component a system identifier associated with the measured electrical resistance value and the component identifier.

The component may be a wire or a bonding strap of an aircraft.

The method may further comprise repeating each of the method steps for each component in a system.

According to a second aspect, the present invention provides a computer-implemented method for testing equipment, the method comprising: measuring a first electrical resistance of a component; storing a value for the first measured electrical resistance in a database; measuring, at a later time, a second electrical resistance of the component; storing a value for the second measured electrical resistance in the database; comparing the first electrical resistance value with the second electrical resistance value; calculating a variance of the first and second measured electrical resistance values; determining whether the variance exceeds a first threshold; and indicating to a user whether or not the variance exceeds the first threshold.

According to a third aspect, the present invention provides a computer-implemented method for testing equipment, the method comprising: measuring a first electrical resistance of a first component in a first system; storing a value for the first measured electrical resistance in a database; measuring, at a later time, a second electrical resistance of a second component in a second system, the second component being equivalent to the first component and the second system being equivalent to the first system; storing a value for the second measured electrical resistance in the database; comparing the first electrical resistance value with the second electrical resistance value; calculating a variance of the first and second measured electrical resistance values; determining whether the variance exceeds a first threshold; and indicating to a user whether or not the variance exceeds the first threshold.

According to a fourth aspect, the present invention provides an apparatus for testing equipment, the apparatus comprising: a current supply for supplying a fixed current through a component; a voltmeter for measuring a voltage across the component; means for calculating a value for an electrical resistance of the component; a memory for storing the electrical rcsistancc valuc; a variance analysis module for comparing and calculating a variance of multiple electrical resistance values of the component; and an indicator for indicating to a user whether or not the variance exceeds a first threshold.

According to a fifth aspect, the present invention provides an apparatus for testing equipment, the apparatus comprising: a voltage supply for supplying a fixed voltage across two electrical components; a micro-ammeter for measuring a leakage current leaking between the electrical components; means for calculating a value for an electrical resistance of the component; a memory for storing the electrical resistance value; a variance analysis module for comparing and calculating a variance of muhiple electrical resistance values of the component; and an indicator for indicating to a user whether or not the variance exceeds a first threshold.

In the method dcscribcd hcrcin, thc term component is intended to include any device, structure or component of a system to be tested, or any cable, wire or other connection between any such component. In the field of aircraft testing, the term component also includes bonding straps. The component may include a electrical component or a non-electrical component, and may be electrically conductive or electrically insulativc. For example, the component may comprise electrical insulation material surrounding an electrical component or insulation material between two or more other components.

Brief Description of the Drawings

Embodiments of the invention will now be described, strictly by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic drawing of an apparatus constructed in accordance with an embodiment of the invention; Figure 2 is a flow diagram showing steps of a process to measure continuity resistance of a component; Figure 3 is a schematic drawing of an apparatus constructed in accordance with an embodiment of the invention; Figurc 4 is a flow diagram showing stcps of a proccss to measure insulation resistance of a component; Figure 5 is a screenshot of an example results file obtained using one embodiment of the present invention; Figure 6 is a table showing example results of a series of tests carried out in accordance with an embodiment of the present invention; Figure 7 is a graph showing the variation in calculated resistance from the table of Figure 6; and Figure 8 is a graph showing the percentage variance from the lowest calculated resistance from the table shown in Figure 6.

Description of the Embodiments

The present invention provides a method and apparatus for testing one or more components of a system. Data resulting from a test carried out on a component or set of components of a first system can be stored for comparison with data relating to a corresponding component or set of components in a second system to check for consistency between corresponding components. Alternatively, data resuhing from a first test carried out on a component or set of components of a system can be stored for comparison with data obtained from one or more subsequent tests carried out on the same component or set of components to check for deterioration in any of the components.

By comparing results of tests carried out on a component or set of components of a first system with results of tests carried out on an equivalent component or set of components in a second or subsequent systems, one is able to check for consistency between systems to ensure that, where two or more systems are expected to be substantially the same and have substantially the same components acting in substantially the same way, those systems and components meet a desired level of similarity. Where the results of tests of a component or set of components of a system are compared with resuhs of tests of the same component or set of components of the same system at a later time, one is able to determine the extent of any dcgradation in that component or set of components which might have occurred.

Taking the example of an aircraft system, a manufacturer is able to use the present invention to check for consistency between components and connections of multiple aircraft manufactured to the same specification. Such a comparison would enable a manufacturer to identify quickly whether the behaviour of a component in one aircraft deviates from the behaviour of an equivalent component in other systems.

A comparison of components can be made by comparing any of a number of characteristics of a component. One characteristic of a component that can be compared is the continuity resistance. Alternatively, another characteristic that can be compared is the insulation resistance. A technique for measuring the insulation resistance of a component is different to a technique for measuring thc continuity rcsistancc of a componcnt. Both techniques arc described below.

Referring to the drawings, Figure 1 shows, schematically, an apparatus 100 for testing a continuity resistance of a component in a system 102. The system 102 may be any electrical system having electrical components, such as an aircraft. The system 102 includes a plurality of electrical components 104a to 104h. While the components 104 are shown simply as wires between two terminals in Figure 1, it will be appreciated that the components may take any form, depending on the system 102. Furthermore, although only eight components are shown in Figure 1, it will be appreciated that the system 102 may include hundreds or even thousands of components 104. The apparatus 100 includes a programmable current supply 106, a voltmeter 108, a programmable switch matrix 114 and a computer 110 having, amongst othcr fcaturcs, a memory 112.

In the embodiment shown in Figure 1, the current supply 106 is connected to, and configured to provide current to, the component 104h being tested. The voltmeter 108 is connected to the component 104h such that it can measure the voltage across the component. The voltmeter 108 is also connected to the computer 110, which stores the measured voltage in the memory 112. The programmable switch matrix 114 serves to isolate the components 104a to 104g which are not being tested, indicated by a dashed line 116. Once the component 104h has been tested, the programmable switch matrix 114 serves to switch the components such that another of the components 104a to 104g is tested, and the other components arc isolatcd.

Figure 2 shows, in a flow diagram, steps of a process 200 for testing a continuity resistance of a component in a system 102.

A fixed current is applied through a component 104 to be tested (hereinafter "component under test") within the system being tested (hereinafter "system under test") (step 202). The fixed current I is supplied by the current supply 106. The programmable switch matrix 114 is used to temporarily connect, for the purpose of the test, the component under test 104h to the current supply 106 and the voltmeter 108.

It is important that the apparatus 100 used to carry out the method is calibrated to a high standard, to cnsurc that tcsts carried out subsequently arc consistent. In one embodiment, therefore, the programmable current supply 106 and the voltmeter 108 are calibrated against a multimeter which is calibrated to a standard recognised by the United Kingdom Accreditation Service (IJKAS) or other equivalent accreditation body.

As the current I is applied through the component under test 104h, a voltage Vi develops across the component. The programmable switch matrix 114 is used to feed the voltage Vi across the component under test 104h to the voltmeter 108 and the voltage is measured (step 204). From the known current I applied to the component under test 104h and the voltage V1 measured across the component under test, a continuity resistance R1 of the component under test is calculated using R1V1/11 (step 206), where R1 is stated in Ohms, V1 is stated in Volts and I is stated in Amperes.

The calculated continuity resistance R1 of the component under test I 04h is stored in the mcmory 112 along with, and associatcd with, an idcntifier for the componcnt under test (step 2O). The identifier may be any number or code that can be used to identif' the component under test 104h. In one embodiment, the identifier is a serial number of the component under test 104h. In addition to the component under test identifier, a system under test identifier may also be stored in the memory along with, and associated with, the calculated continuity resistance R1 and the component under test identifier (step 210).

Figure 3 shows, schematically, an apparatus 300 for testing an insulation resistance between components in a system 302. That is to say, the apparatus 300 allows a user to test the resistance of the insulation between components in the system 302. As with the embodiment shown in Figure 1, the system 302 may be any electrical system. The system 302 includes a plurality of electrical components 304a to 304h. Insulative material is provided between each adjaccnt componcnt 304a to 304h to electrically insulatc onc componcnt from another. While the components 304 are shown simply as wires between two terminals in Figure 3, it will be appreciated that the components may take any form, depending on the system 302.

Furthermore, although only eight components are shown in Figure 3, it will be appreciated that the system 302 may include hundreds or even thousands of components 304. The apparatus 300 includes a programmable high-voltage power supply 306, a micro-ammeter 308, a programmable switch matrix 114 and a computer 310 having, amongst other features, a memory 312.

In the embodiment shown in Figure 3, the programmable high-voltage power supply 306 is connected to, aM configured to provide a voltage across, the components 304g and 304h being tested. The micro-ammeter 308 is connected to the component 304g such that it can mcasure thc lcakagc current lcaking bctwecn the componcnts. Thc lcakagc currcnt is current leaking throigh the insulation around each component, or between adjacent components.

The micro-ammeter 308 is also connected to the computer 310, which stores the measured current in the memory 312. The programmable switch matrix 314 serves to isolate the components 304a to 304f which are not being tested, indicated by a dashed line 316. Once the components 304g and 304h have been tested, the programmable switch matrix 314 serves to switch the components such that another pair or group within the components 304a to 304h are tested, and the other components are isolated.

Figure 4 shows, in a flow diagram, steps of a process 400 for measuring an insulation resistance between components under test 304g and 304h.

A fixed voltage is applied across two components under test 304g and 304h (step 402). The fixed voltage is supplied using the programmable high-voltage power supply 306. A programmable switch matrix 314 is used to isolate the components under test 304g and 304h from any other components 304a to 304f in the system 302, and from any wires or cables used to connect the components to one another.

It is important that the apparatus 300 used to carry out thc method is calibrated to a high standard, to ensure that tests carried out subsequently are consistent. In one embodiment, therefore, the programmable high-voltage power supply 306 and micro-ammeter 308 are calibrated against a multimeter which is calibrated to a standard recognised by the United Kingdom Accreditation Service (UKAS) or other equivalent accreditation body.

As a voltage V2 is applied across the components under test 304g and 304h, any current leaking between the components is measured using the micro-ammeter 308 (step 404). From the known test voltage V2 applied across the components under test 304g and 304h and the measured current 2, an insulation resistance R2 between the components under test is calculated using R2=V2/12 (step 406), where R2 is stated in Ohms, V2 is stated in Volts and 2 is stated in Amperes.

The calculated insulation resistance R2 of the components under test 304g and 304h is stored in the memory 312 along with, and associated with, identifiers for the components under test (step 408). The identifiers may be any number or code that can be used to identify the components under test 304g and 304h. In one embodiment, the identifiers are serial numbers of the components under test 304g and 304h. In addition to the component identifiers, a system identifier to identify the system under test may also be stored in the memory 3 12 along with, and associated with, the calculated resistance, R2, and the component identifiers (step 410).

It will be appreciated that, while the processes 200 and 400 described above are concerned with calculating the continuity and insulation resistances of individual components under test, a system to be tested, such as an aircraft, typically includes a large number of components and connections between the components, each of which must be tested. Thus, the above processes 200 and 400 may be repeated multiple times so as to record a resistance for every component and connection in the system under test. The resistance calculated for each component is recorded in the memory 112 and 312.

Figure 5 is a screenshot of an example set of results which have been exported to a computing device and displayed in a spreadsheet 500. The spreadsheet 500 includes a plurality of columns 502 to 510 listing data recorded during the processes 200 and 400.

Column 502 is entitled "Test_ID" and lists an identifier for the test that the results relate to.

Column 504 is entitled "ResultID" and lists an identifier for cach result in the test. For example, each unique value in the ResultID column 504 might indicate a different component under test or connection being tested. Column 506 is entitled "Name" and lists a name for each component under test or connection being tested. In the example shown in Figure 5, the first row relates to the first result in the test (ResultID has a value 1), and is allocated a name "Conn 1". Column 508 is entitled "Nominal" and lists values of resistance measured during the test. Column 510 is entitled "UOF" and indicates the units of measurement for the results in the preceding column 508. Thus, it is clear that, for the first component (Conn 1), a resistance of 0.690 Ohms was calculated.

While the spreadsheet 500 of Figure 5 includes only ten rows, it will be appreciated that the actual number of rows in a results spreadsheet may be greater or smaller and will depend on the number of componcnts and/or connections tested in a particular system.

Once a test has been completed, and the values of resistance for each component in a system being tested have been calculated and recorded, the data can be analysed. As mentioned previously, data recorded using the processes 200 and 400 can be used in a number of ways.

Firstly, a first set of data relating to components in a system can be compared against a second and/or subsequent sets of data relating to the same components in the same system, which are measured at a later time. From such a comparison, it would be possible to identii the extent to which any changes have occurred to any of the components over the period of time between successive tests. Secondly, a set of data relating to components in a first system can be compared against a set of data relating to corresponding components in a second system intended to be substantially the same as the first system. From such a comparison it would be possible to idcnti any differences between components in systems in which there should be no measurable differences. For example, if an aircraft manufacturer constructs ten aircraft all to the same specification, then there should be no differences between the components or connections of one aircraft and the corresponding components or connections in any other of the ten aircraft.

In order to compare the results of tests, one embodiment of the present invention carries out variance analysis on the results of a plurality of tests. The variance analysis may be carried out by a computer on which data from a plurality of tests is stored, or on a separate computer onto which data is loaded for analysis.

According to one embodiment, variance analysis of a plurality of data sets obtained from subsequent tests carried out on a single system involved identifying the smallest calculated resistance for a particular component under test. The variance of the calculated resistance from the smallest calculated resistance can then be calculated as a percentage variance.

An example set of results on which variance analysis has been carried out is shown in a table 600 in Figure 6. Colunm 602 is entitled "Result No." and identifies each of the test results.

In the example shown in Figure 6, the particular component to which the results relate has been tested twenty five times. Column 604 is entitled "Calculated Resistance in Ohms" and lists the calculated resistance for the component for each result. The smallest calculated resistance in the lists of calculated resistances 604 is 0.010 Ohms, shown ringed and labelled 606. Column 608 is entitled "Positive variance analysis against best result" and lists, as percentages, the difference in the calculated resistance from the smallest calculated resistance 606.

Figures 7 and 8 show the results listed in the table 600 in graphical form. Figure 7 shows a graph 700 of the calculated resistance (604 in Figure 6) plotted against the test result number (602 in Figure 6). It is evident from plot 700 that the calculated resistance of the component under test remains substantially constant until around result number 19, when the calculated resistance begins to increase with each subsequent test. At test 25, the calculated resistance of the component under test increases significantly from 0.025 Ohms to 0.066 Ohms. Figure 8 shows a graph 800 of the percentage variance of the calculated resistance (608 in Figure 6) from the smallest calculated resistance 606 plotted against the test result number (602 in Figure 6). From Figure 8, it is clear to see that the percentage variance of the test results is relatively small until amund result number 19, when the variance increases. The variance of the calculated resistance of test 25 from the smallest calculated resistance (which was calculated in test number 1) is 560%.

It is clear fitm the large increase between tests 24 and 25, visible in the graphs of Figures 7 and 8, that a significant change has occurred in the component under test which has lcd to a large increase in its resistance. Such a change might, tbr example, be indicative of a fault with a component, or a break in a connection between two components. It can also be concluded from the gradual increase in calculated resistance between tests 19 and 24 that some deterioration in the component under test had occurred or was beginning to occur before the apparent failure of the component at test 25. The gradual deterioration might act as a warning sign that the component is beginning to deteriorate, and should be repaired or replaced.

In one embodiment of the present invention, a user is infbrmed, fbr example by an audio or visual indicator, when the calculated resistance of a test result varies flDm the smallest calculated resistance by more than a predetermined amount. In another embodiment, the invention informs a user when the variance between a calculated resistance and the smallest calculated resistance exceeds various thresholds. For example, when the variance in the calculated resistance is below a first threshold, then the component under test is considered to be functioning correctly, and a computer displaying the test results displays a green indicator.

The green indicator informs thc user that no issues have bccn identified concerning the component under test. If the variance between a calculated resistance and the smallest calculated resistance is between the first threshold and a second threshold, then the computer displays an amber indicator. The amber indicator informs the user that some deterioration of the component under test appears to have taken place. If the variance between a calculated resistance and the smallest calculated resistance exceeds the second threshold, then the computer displays a red indicator. The red indicator informs the user that a significant change in the calculated resistance of the component under test has occurred, and that further investigation ofthe component or connection should be made to determine whether or not the component should be repaired or replaced.

The example described above with reference to Figures 6, 7 and 8, concerns carrying out multiple tests on one or more components in a system under test. It will be apparent that a similar analysis of results could be made of tests carried out on corresponding components in a plurality of systems which arc intended to be significantly the same. In that case, a variance between a calculated resistance and the smallest calculated resistance exceeding a predetermined threshold for a particular component can be indicative that the component is faulty, or that a connection between two components is not complete. If it becomes apparent that a particular component in one system under test has a resistance that varies significantly (that is, a variance exceeding a predetermined threshold) from one or more other systems which should have substantially the same components, then the component exhibiting an unexpected resistance can be checked and repaired or replaced if required.

So far, the invention has been described in terms of individual embodiments. However, those skilled in the art will appreciate that various embodiments of the invention, or features from one or more embodiments, may be combined as required. It will be appreciated that various modifications may be made to these embodiments without departing from the scope of the invention, which is defined by the appended claims.

Claims

Claims 1. A computer-implemented method for testing equipment, the method comprising: measuring a first electrical resistance of a component; storing a value for the first measured electrical resistance in a database; measuring a second electrical resistance of a component; storing a value for the second measured electrical resistance in a database; comparing the first electrical resistance value with the second electrical resistance value; calculating a variance of the fir st and second measured electrical resistance values; determining whether the variance exceeds a first threshold; and indicating to a user whether or not the variance exceeds the first threshold.
2. A computer-implemented method according to claim 1, wherein the first measured electrical resistance and the second measured electrical resistance are stored in the same database.
3. A computer-implemented method according to claim 1 or claim 2, wherein the component is a component of an aircraft.
4. A computer-implemented method according to claim I or claim 2, wherein the component is in a system; and wherein the first electrical resistance is measured at a first time, and the second electrical resistance is measured at a second, later time.
5. A computer-implemented method according to claim 4, wherein the system is an aircraft.
6. A computer-implemented method according to claim I or claim 2, wherein the component of which the first electrical resistance is measured comprises a component of a first system and the component of which the second electrical resistance is measured comprises a component of a second system; and wherein the component of the second system is equivalent to the component of the first system.
7. A computer-implemented method according to claim 6, wherein the first system and the second system are aircraft.
8. A computer-implemented method according to claim 6 or claim 7, further comprising allocating a unique identifier to each componcnt.
9. A computer-implemented method according to claim? or claim 8; wherein the component of the first system is one of a first plurality of components, and the componcnt of the sccond system is one of a second plurality of components; and wherein said measuring comprises measuring an electrical resistance for each component of the first and second plurality of components.
10. A computer-implemented method according to any of the preceding claims, wherein said indicating comprises displaying a first indication to a user if the variance is below the first threshold, displaying a second indication to the user if the variance is between the first threshold and a second threshold, and displaying a third indication to the user if the variance exceeds the second threshold.
11. A computer-implemented method according to claim 10, wherein said fir st indication is a first colour, said second indication is a second colour and said third indication is a third colour.
12. A computer-implemented method according to any of the preceding claims, wherein said measuring of electrical resistance comprises applying a fixed current to the component, measuring the voltage across the component, and dividing the measured voltage by the applied current.
13. A computer-implemented method according to claim 12, wherein the method is a method for testing continuity resistance of the component; and wherein the fixed current is supplied by a low voltage power supply.
14. A computer-implemented method according to any of claims I to 11, wherein said measuring of electrical resistance comprises applying a fixed voltage across two electrical components, measuring a leakage current flowing between the electrical components, and dividing the applied voltage by the measured current.
15. A computer-implemented method according to claim 14, wherein the method is a method for testing insulation resistance of the component; and wherein thc fixcd voltage is supplied by a high voltage power supply.
16. A computer-implemented method according to any of the preceding claims, further comprising: storing for each componcnt a component identifier associated with the measured electrical resistance value.
17 A computer-implemented method according to claim 16, further comprising: storing for each component a system identifier associated with the measured electrical resistance value and the component identifier.
18. A computer-implemented method according to any of the preceding claims, wherein component is a wire.
19. A computer-implemented method according to any of claims 1 to 17, wherein component is a bonding strap ofan aircraft.
20. A computer-implemented method according to any of claims 1 to 17, wherein the component is an electrically insulative component.
21. A computer-implemented method according to any of claims 1 to 17, wherein the component comprises insulation between a pair of electrically conductive components.
22. A computer-implemented method according to any of the preceding claims, further comprising: repeating each of the method steps for each component in a system.
23. A computer-implemented method for testing equipment, the method comprising: measuring a first electrical resistance of a component; storing a value for the first measured electrical resistance in a database; measuring, at a later time, a second electrical resistance of the component; storing a value for the second measured electrical resistance in the database; comparing the first electrical resistance value with the second electrical resistance value; calculating a variance of the first and second measured electrical resistance values; determining whether the variance exceeds a first threshold; and indicating to a user whether or not the variance exceeds the first threshold.
24. A computcr-implcmcntcd mcthod for tcsting cquipmcnt, thc method comprising: measuring a first electrical resistance of a first component in a first system; storing a value for the first measured electrical resistance in a database; measuring, at a later time, a second electrical resistance of a second component in a second system, the second component being equivalent to the first component and the second system being equivalent to the first system; storing a value for the second measured electrical resistance in the database; comparing the first electrical resistance value with the second electrical resistance value; calculating a variance oft first and second measured electrical resistance values; determining whether the variance exceeds a first threshold; and indicating to a user whether or not the variance exceeds the first threshold.
25. An apparatus for testing equipment, the apparatus comprising: a current supply for supplying a fixed current to a component a voltmeter for measuring a voltage across the component; means for calculating a value for an electrical resistance of the component a memory for storing the electrical resistance value; a variance analysis module for comparing and calculating a variance of multiple electrical resistance values of the component; and an indicator for indicating to a user whether or not the variance exceeds a first threshold.
26. An apparatus for testing equipment, the apparatus comprising: a voltage supply for supplying a flxcd voltagc across two clcctrical componcnts; a micm-ammeter for measuring a leakage current leaking between the electrical components; means for calculating a value for an electrical resistance of the component insulation a memory for storing the electrical resistance value; a variance analysis module for comparing and calculating a variance of multiple electrical resistance values of the component insulation; and an indicator for indicating to a user whether or not the variance exceeds a first threshold.
27. An apparatus for pcrtbnning a mcthod according to any of thc prcccding claims.
28. A computer-implemented method substantially as hereinbefore described, with reference to, or as shown in, the drawings.
29. An apparatus substantially as hereinbefore described, with reference to, or as shown in, the drawings.Amendments to the claims have been made as follows: Claims 1 A computer-implemented method for testing equipment, the method comprising: measuring a first electrical resistance of an aircraft component; storing a value for the first measured electrical resistance in amemory; measuring a second electrical resistance of an aircraft component; storing a value for the second measured electrical resistance in a memory; comparing the first electrical resistance value with the second electrical resistance value; calculating a difference between the first and second measured electrical resistance values as a percentage of the first measured electrical resistance value; determining whether the percentage difference exceeds a first threshold; and indicating to a user whether or not the percentage difference exceeds the first threshold.2. A computer-implemented method according to claim 1 wherein the first measured electrical resistance and the second measured electrical resistance are stored in the same o memory. (03. A computer-implemented method according to claim 1 or claim 2, wherein the aircraft component is in a system; and wherein the first electrical resistance is measured at a first time, and the second electrical resistance is measured at a second, later time.4. A computer-implemented method according to claim 3, wherein the system is an aircraft.5. A computer-implemented method according to claim I or claim 2, wherein the aircraft component of which the first electrical resistance is measured comprises an aircraft component of a first system and the aircraft component of which the second electrical resistance is measured comprises an aircraft component of a second system; and wherein the aircraft component of the second system is equivalent to the aircraft component of the first system.6. A computer-implemented method according to claim 5, wherein the first system and the second system are aircraft.7. A computer-implemented method according to daim 5 or claim 6, further comprising allocating a unique identifier to each aircraft component.8. A computer-implemented method according to claim 6 or claim 7; wherein the aircraft component of the first system is one of a first plurality of aircraft components, and the aircraft component of the second system is one of a second plurality of aircraft components; and wherein said measuring comprises measuring an electrical resistance for each aircraft component of the first and second plurality of aircraft components.9. A computer-implemented method according to any of the preceding claims, wherein said indicating comprises displaying a first indication to a user if the difference is below the first threshold displaying a second indication to the user if the difference is between the first C\I threshold and a second threshold, and displaying a third indication to the user if the difference o exceeds the second threshold. (0(\,j 10. A computer-implemented method according to claim 9, wherein said first indication is a first colour, said second indication is a second colour and said third indication is a third colour.1]. A computer-implemented method according to any of the preceding claims, wherein said measuring of electrical resistance comprises applying a fixed current to the aircraft component, measuring the voltage across the aircrafl component, and dividing the measured voltage by the applied current.12. A computer-implemented method according to claim 11, wherein the method is a method for testing continuity resistance of the aircrafl component; and wherein the fixed current is supplied by a low voltage power supply.13. A computer-implemented method according to any of claims I to 10, wherein said measuring of electrical resistance comprises applying a fixed voltage across two electrical aircraft components, measuring a leakage current flowing between the electrical aircraft components, and dividing the applied voltage by the measured CulT ent.14. A computer-implemented method according to claim 13, wherein the method is a method for testing insulation resistance of the aircraft component; and wherein the fixed voltage is supplied by a high voltage power supply.15, A computer-implemented method according to any of the preceding claims, further comprising: storing for each aircraft component an aircraft component identifier associated with the measured electrical resistance value.16 A computer-implemented method according to claim 15, further comprising: storing for each aircraft component a system identifier associated with the measured electrical resistance value and the aircraft component identifier.17. A computer-implemented method according to any of the preceding claims, wherein o aircraft component is a wire. (0(\,j 18, A computer-implemented method according to any of claims Ito 16, wherein aircraft component is a bonding strap of an aircraft.19. A computer-implemented method according to any of claims 1 to 16, wherein the aircraft component is an electrically insulative aircraft component.20. A computer-implemented method according to any of claims 1 to 16, wherein the aircraft component comprises insulation between a pair of electrically conductive aircraft components.21 A computer-implemented method according to any of the preceding claims, further comprising: repeating each of the method steps for each aircraft component in a system.22. A computer-implemented method for testing equipment, the method comprising: measuring a first electrical resistance of an aircraft component; storing a value for the first measured electrical resistance in a memory; measuring, at a later time, a second electrical resistance of the aircraft component; storing a value for the second measured electrical resistance in the memory; comparing the first electrical resistance value with the second electrical resistance value; calculating a difference between the first and second measured electrical resistance values as a percentage of the first measured electrical resistance value; detennining whether the percentage difference exceeds a first threshold; and indicating to a user whether or not the percentage difference exceeds the first threshold, 23. A computer-implemented method for testing equipment, the method comprising: measuring a first electrical resistance of a first aircraft component in a first system; storing a value for the first measured electrical resistance in a memory; measuring at a later time a second electrical resistance of a second aircraft C\I component in a second system, the second aircraft component being equivalent to the first o aircraft component and the second system being equivalent to the first system; (0 storing a value for the second measured electrical resistance in the memory; comparing the first electrical resistance value with the second electrical resistance value; calculating a difference between the first and second measured electrical resistance values as a percentage of the first measured electrical resistance value; determining whether the percentage difference exceeds a first threshold; and indicating to a user whether or not the percentage difference exceeds the first threshold, 24. A computer-implemented method according to any of the preceding claims, wherein the calculating a difference between the first and second measured electrical resistance values comprises calculating a varhmce, 25. An apparatus for testing equipment, the apparatus comprising: a current supply for supplying a fixed current to an aircraft component; a voltmeter for measuring a voltage across the aircraft component; means for calculating a value for an electrical resistance of the aircraft component; a memory for storing the electrical resistance value; an analysis module for comparing and calculating a difference between multiple electrical resistance values of the aircraft component as a percentage of a first of the multiple electrical resistance values; and an indicator for indicating to a user whether or not the percentage difference exceeds a first threshold.26. An apparatus for testing equipment, the apparatus comprising: a voltage supply for supplying a fixed voltage across two electrical aircraft components; a micro-ammeter for measuring a leakage current leaking between the electrical aircraft components; means for calculating a value for an electrical resistance of the aircraft component insulation; a memory for storing the electrical resistance value- r-an analysis module for comparing and calculating a difference between multiple o electrical resistance values of the aircraft component insulation as a percentage of a first of the multiple electrical resistance values; and (\,j an indicator for indicating to a user whether or not the percentage difference exceeds a first threshold.27, M apparatus according to claim 25 or claim 26, wherein the analysis module comprises a variance analysis module for comparing and calculating a variance of the multiple electrical resistance values.28. An apparatus for testing equipment, the apparatus comprising: means for measuring a first electrical resistance of an aircraft component; a memory for storing a value for the first measured electrical resistance; means for measuring a second electrical resistance of an aircraft component; a memory for storing a value for the second measured electrical resistance; means for comparing the first electrical resistance value with the second electrical resistance value; means for calculating a difference between the first and second measured electrical resistance values as a percentage of the first measured electrical resistance value; means for determining whether the percentage difference exceeds a first threshold; and means for indicating to a user whether or not the percentage difference exceeds the first threshold.29. A computer-implemented method substantially as hereinbefore described, with reference to, or as shown in, the drawings.

30, An apparatus substantially as hereinbefore described, with reference to, or as shown in, the drawings. (4 (0