Production line testing can help cut down on re-call costs and late delivery penalities. Here, Greg Brown looks at electrical safety testing in the manufacturing environment.

With verification of the safe operation and functionality of electrical products being vital to ensure compliance with established industry standards and maintain customer confidence, the focus has switched from whether safety testing is needed to the actual extent of testing required.
The requirement to ensure conformance with standards through the manufacturing process is made clear by the various regulatory and legislative authorities, but a common reaction still seems to be 'does this mean I have to do 100 per cent testing?', followed by a quick retreat into discussions that aim to reduce an erroneously perceived time/cost burden, often quoting ISO9000 procedures and focusing on sample testing as a suitable solution.
This approach tends to exclude a closer evaluation of the concept of 100 per cent testing - which is to ensure and maintain product safety.
Batch sampling is essentially designed to determine that type test and build instructions are being maintained via a set of 'working standards' and relies on there being a traceable scientific relationship between the 'sample' and the rest of the batch. The assumption being that if the sample shows conformance, then the rest of the batch also complies. In many manufacturing processes 'sampling' may be satisfactory, but when the issue is customer safety, can anyone take this risk?
In order to maintain a proper scientific relationship, back to the 'type approved product', testing of the batch sample should really involve a repeat of the 'type test' and this could involve:
u The use of external test houses.
u Or the transfer of the sample to a dedicated, in-house, test laboratory.
u Skilled and expensive labour.
u Specialised (and usually high cost) test equipment.
u Complex, time consuming, test routines.
u Possible destruction of test sample.
Taking a typical batch sampling routine as an example, the following scenario can be envisaged.
Risk analysis determines a procedure for testing one sample product for every 100 that come off the assembly line. The sample is sent to the laboratory where it undergoes rigorous testing and fails. Strictly speaking, production should now be halted until the cause and extent of the fault is identified. This should include recalling and testing not only the remaining 99 items of the particular batch, but any items produced since the sample was taken.
The cost of this exercise can be worked out in terms of:
u Re-call costs (time, labour, discard packaging etc.) - even greater if products have left the factory.
u Testing costs (which will now include skilled labour).
u Rework costs (time, labour, parts if any).
u Lost production (highly unlikely that all items are salvageable).
u Late delivery penalties.
It may be a sobering experience to investigate your ISO9000 're-call' procedures and cost them accordingly.
The above paints a very black picture and it might be argued that this worst-case scenario only applies if the sample fails - but would anyone feel comfortable knowing that an electric drill or appliance used in a workshop has only a 1 in 100 chance of NOT causing electrocution?
Similarly, it is clearly in the interests of manufacturers of finished products that the safety critical components used to assemble a product are satisfactory - preferably before being incorporated into the product.
Against this background it is clear there are increasing numbers of manufacturers of electrical products who wish to check supplied components before or during their own product assembly. Among such companies, there has been the implicit rejection of batch sampling as a viable test method and recognition of the advantages of 100 per cent component testing:
u Allows for pro-active identification of problems and defects before assembly.
u Increases confidence in finished products.
u Reduces likelihood of product re-work.
u Allows the cost of failures to be recovered from the supplier more easily.
By completing the manufacturing cycle with 100 per cent product testing, significant information can be gathered and used to improve and refine manufacturing processes and techniques. Identifiable reasons for product failures can be highlighted and quickly acted upon. Even simple fault counters can indicate particular areas of the build phase that may require further investigation.
Another major plus for 100 per cent testing is the development of a competitive advantage, in that a component supplier company's ability to offer fully tested components/products reduces the need for the customer to carry out their own testing, thus offering a level of added value that can be translated into increased profitability, plus customer confidence and loyalty.
From the above is can be seen that batch testing has many identifiable shortcomings and that 100 per cent testing is being advocated, but what is meant by 100 per cent testing?
Firstly it should be noted that this article related to the electrical safety requirements and it is Clare's experience in this area that the value of three main tests for ensuring product safety continues to be:
u High current earth bond measurement.
u High voltage flash test.
u Insulation resistance measurement.
A number of concerns have been made against such an approach, usually on the basis of time and cost, but these can be countered.
On the time factor, misconceptions arise between Type testing requirements and the established practices for 100 per cent Production Line testing. For example, comprehensive test stations are available that can apply all three basic safety tests in cycles as short as two-three seconds per product. Referring back to the earlier example, all 100 products could have been tested in 5 minutes.
In terms of cost, equipment can be expensive if the Type test trap is fallen into again, but there are a number of production line test systems available, which are much more reasonably priced. With simple to use set-up and control features, these test stations can be readily incorporated into the production environment without the need for highly skilled labour.

The Transtar example

Given the tremendous variety in size, shape and performance characteristics of the wide range of electrical products now manufactured, it is often the case that customised electrical safety testing solutions need to be developed to meet specific production line requirements.
One such example is provided by work recently undertaken for lighting equipment manufacturer Transtar by safety testing specialists Clare Instruments.
For more than 50 years Transtar has been a leading manufacturer of control gear for the lighting industry. Over the years the company has extended its product range to include a wide variety of control gear for fluorescent and high intensity discharge (HID) lamps, including high frequency ballasts. One of the company's most recent additions is a new low power, low-pressure sodium ballast which gives users the benefits of installing a high power factor unit without the need for connecting a separate capacitor across the mains input.

Lighting control ballasts

As part of this commitment to product development and user satisfaction, Transtar recently introduced new testing facilities for its full range of 50Hz control ballasts.
Lighting control ballasts are the drive units for gas discharge lamps and use either an electromagnetic (50Hz) circuit or high frequency electronics.
The electromagnetic ballasts in particular are becoming more popular among luminaire manufacturers because of their energy saving features and comprise an iron core with a winding of insulated copper. The lamination stack consists of electrical grade mild steel and is attached to a mild steel base plate, to which terminal blocks are fixed.
The whole unit is vacuum impregnated with an unsaturated polyester resin system to improve reliability, reduce noise and ensure high thermal and insulation performance with good knock resistance.

Testing demands

When used in luminaires, the ballast is grounded through the base plate. At the end of the production process the need was therefore to carry out effective earth bond and flash tests to ensure the electrical safety of the unit and particularly that reliable contact had been established between the lamination stack and the base plate.
However, the presence of the external resin coating provided a problem, particularly with the earth bond test. This test ensures the proper and secure connection of the metal case to the mains earth reference using test probes and relies on all individual external metal surfaces being tested - a process rendered almost impossible by the polyester resin coating.

Tried and tested

To meet these needs, a customised solution was developed to meet Transtar's exacting quality assurance requirement for fully integrated end of line testing which was to include checking both the electrical safety and functional parameters of its product.
The Clare design team was able to select and configure the various test modules form the company's wide range of products into a bespoke system. However, the major concern to overcome was how to apply the tests to the product in a quick, simple and operator friendly manner.
The use of a safety enclosure is regarded as essential for such applications in that it provides operator safety, product location and can be readily interfaced to the test instrument for initiating automatic sequencing of the required tests.
Incorporating the necessary fixturing within the enclosure to automatically apply the test probes to the various test points - lamination stack, mounting plate and ballast winding terminals - also required careful consideration given the nature of the product. For this particular application it was therefore decide that pneumatically driven test heads would be the most appropriate solution, providing the additional power required for effective and reliable contact.

Given that the base material of the laminations and mounting plate were encased in a resilient insulating resin coating, extensive research and experimentation was also required to develop the optimum probe tip design. This not only had to satisfy the criteria for making effective contact through the resin to the base metal, but also had to stand up to the high volume throughput of busy production cells.
Other features incorporated into the overall design provide clear identification of faulty product through clear audible and visual warnings. Isolation of all test outputs is also achieved automatically whenever the enclosure is opened.
The end result is a fully integrated test and measurement system that provides quick and simple testing of finished ballast control products coupled with operator safety, giving the manufacturer major benefits in the quest for maximum production efficiency at minimum unit cost.

Greg Brown is with Clare Instruments, Worthing, West Sussex. UK. www.clareinstruments.com