Plant & Works Engineering

Automated traceability

Published:  23 June, 2007

John Barnett of test instrument manufacturer Clare Instruments describes how the integration and automation of electrical testing systems can enhance production control and data collection capabilities in modern manufacturing processes.

In recent years, manufacturers of electrical products and components have become increasingly aware that the implications of electrical safety testing go much further than the design and development stages.

The need for electrical safety testing is dictated by stringent safety requirements and the manufacturers' liability in relation to technical standards such as the Low Voltage Directive (CE Mark) and these responsibilities extend to the end of the production line.

As a result, the verification of functionality and the safe operation of electrical products is now recognised as absolutely vital and production line safety testing has become an essential part of the electrical product manufacturing process.

The mandatory requirement for 100% testing, with the storage of electronic test records to substantiate the test process, invariably requires the testing stages to be undertaken as an integral part of the production process.

In response to this situation, manufacturers of electrical safety testing instrumentation have developed a comprehensive range of test equipment suitable for use as individual instruments in product development or quality control laboratories or as integrated, semi or fully automatic test stations used on the production line.

The manufacturing process for many electrical or electronic equipment requires a variety of tests to be undertaken in keeping with the type and complexity of the end product. Given the tremendous variety in size, shape and performance characteristics of the wide range of appliances and electrical products now manufactured, it is often the case that customised instrumentation is developed to meet specific production line electrical test requirements.   

The modular design of the electrical test instrumentation itself allows specific test station configurations to be developed quickly and effectively.  The use of specially designed enclosures and test fixtures with customised contact points or adaptor units, interfaced with the test instrument, means that fully integrated stations can be developed for virtually all electrical and electronic products, whatever their geometry or surface finish.

In the manufacturing environment, however, time is money and the justification for the incorporation of automated instrumentation is rarely made on technical grounds alone. Improving productivity, efficiency and quality are the driving force behind new smarter testing solutions - with these factors also providing a very quick payback period on any capital investment made on process improvement.

In this respect the time taken for completion of the test cycle is critical. Enforcing just in time manufacturing with unit production times of 5 minutes is clearly of little value if the end of line test station takes 10 minutes to complete all tests. Another significant productivity improvement is that by automating the test process, test operator time and cost can be removed from the process.

In response, new test control and instrumentation systems are now available which are capable of applying typical earth/ground bond, high voltage flash/Hipot/dielectric withstand and insulation resistance safety tests in timescales as fast as 2-3 seconds per product. In addition, as a means of streamlining test stations and matching productivity rates, specially designed holders or jigs allow for the testing of multiple products at the same time.

In this way fully programmable electrical safety and functional test instruments can be adapted and integrated for use in bespoke test systems using proprietary control and instrumentation software such as Lab View, running on low cost rugged industrial touch screen PCs.

Another benefit of test automation is that the process can be de-skilled and operator safety maximised. Although testing should always be undertaken by competent staff, in many cases the use of pre-set test parameters, protected by password and/or failsafe devices, means that the use of highly skilled or experienced test staff may not always be a pre-requisite, allowing greater flexibility in the use of production or assembly line personnel.

In conjunction with these technical and manufacturing considerations quality control factors have placed greater emphasis on the importance of 100% testing regimes as a safeguard against any product liability problems. Efficient production line test procedures can eliminate potential re-call costs, re-working costs, lost production and late delivery problems which can all be associated with alternative batch sampling routines.

Against this background, knowing why safety tests are necessary and integrating them with the production line is one thing, but being able to prove compliance of individual products is another matter particularly in the subsequent event of a failure or accident linked to use of the product in the marketplace.

It is therefore the demands of modern ISO quality control systems and the consumer that are now placing greater importance on the automatic traceability of test results.

The only way to prove that an appliance or item was tested properly is through traceable documentation. With conventional manual recording systems being fraught with potential errors and problems, the most effective way to prove compliance with relevant standards is to use test instrumentation that not only automates the test process but is also capable of recording electronic results at the same time.

As well as storing results for later printout or downloading to a PC, such systems can be combined with pass/fail label printers complete with serial numbers and/or linked to bar code identification.

However, in data collection terms, networking with central management information systems can also allow the test station to become a vital data collection point.

Usually located at the end of the production line, the test station is one of the final quality inspection tools and is therefore able to gather important statistical process control (SPC) data that can directly affect long term quality and productivity.

For example, the test station can identify and record type of failure modes, operator performance and production throughput associated with particular shifts and operators. Other data that can be recorded includes first time pass rates and qualitative values for any function and performance tests that are conducted outside the legal requirements for CE marking, but which may directly affect overall product quality and the level of field returns.

With the increasing trend towards outsourcing production, the effective collection of SPC data is particularly important when manufacturing processes are remote from central management or product design teams, as real-time data can be gathered on the product failure modes/productivity rates as the products are manufactured via a web link to the instrumentation system deployed on the line. 

In our experience productivity and quality improvements gained from SPC can improve the first time pass rate and lower the returns rate very significantly, with one client revealing that the first time pass rate had increased from 82% to 94% and returns had dropped from 3% to 0.5% - with these numbers being directly linked to a dramatic increase in profitability. 

In this way, proper traceable process documentation generated automatically by the test instrumentation minimises product liability, provides effective proof that a product is safe at the end of the manufacturing process and facilitates process improvements (SPC) that give much broader productivity and quality benefits.

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