scenario presents a very bleak picture, and it might be
argued that this worst-case example applies only if the
sample fails. But would anyone feel comfortable knowing
that an electric drill or an appliance used in a workshop
has only a 1 in 100 chance of not causing electrocution?
it is clearly in the interests of manufacturers of finished
products that the safety-critical components used to assemble
a product are satisfactorypreferably before being incorporated
into the product. Batch testing has many identifiable
shortcomings, making 100% testing a more attractive alternative.
this grim background, increasing numbers of manufacturers
of electrical products are checking supplied components
before or during their own product assembly. Such companies
have essentially rejected batch sampling as a viable test
is important to define what is meant by 100% testing.
Testing 100% of components allows for identification of
problems and defects before assembly, increases confidence
in finished products, and reduces likelihood of product
rework. It also allows the cost of failures to be recovered
from suppliers more easily.
completing the manufacturing cycle with 100% product testing,
the information gathered can be used to improve and refine
manufacturing processes and techniques. Identifiable causes
of product failures can be highlighted and acted upon
quickly. Even simple fault counters can indicate particular
areas of the build phase that may require further investigation.
It should be noted that the three main tests required
to ensure product safety are high-current earth bond (ground)
measurement, high-voltage flash (hipot or dielectric strength)
test, and insulation-resistance measurement.
implementation of 100% testing enables companies to develop
a competitive advantage. Such testing enables component
suppliers to offer fully tested components or products,
which reduces the testing burden on manufacturers.
number of concerns have been raised questioning the viability
of a 100% testing approach. These concerns usually surround
time and cost issues and are easily addressed.
arise between type-testing requirements and the established
practices for 100% production-line testing. For example,
comprehensive test stations are available that can apply
all three basic safety tests in cycles of as little as
23 seconds per product. Referring back to the example
discussed earlier, all 100 products could have been tested
in just 5 minutes.
number of production-line test systems available are reasonably
priced. With simple-to-use setup and control features,
these test stations can be readily incorporated into a
production environment without the need for highly skilled
labor. Equipment for type testing, on the other hand,
can be quite expensive.
the tremendous variety in size, shape, and performance
characteristics of electrical products, customized electrical
safety-testing solutions must often be developed to meet
specific production-line requirements. For example, Clare
Instruments (Goring-by-Sea, UK) recently customized a
system for lighting equipment manufacturer Transtar (Newcastle
Upon Tyne, UK).
more than 50 years, Transtar has manufactured control
gear for the lighting industry. The company has extended
its product range to include a wide variety of control
gear for fluorescent and high-intensity-discharge lamps,
including high-frequency ballasts. Lighting control ballasts
are the drive units for gas discharge lamps and use either
an electromagnetic (50-Hz) circuit or high-frequency electronics.
One of the company's most recent additions is a low-power,
low-pressure sodium ballast that gives users the benefits
of installing a high-power-factor unit without the need
for connecting a separate capacitor across the mains input.
New testing facilities were required to test this range
of 50-Hz control ballasts.
ballasts have become more popular among luminaire manufacturers
because of their energy-saving features, and because they
comprise an iron core with insulated-copper winding. The
lamination stack consists of electrical-grade mild steel.
It 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.
range of lighting control units from Transtar.
used in luminaires, ballasts are grounded through the
base plate. Therefore, at the end of the production process,
effective earth bond and flash tests were necessary to
ensure the electrical safety of each unit. It was particularly
important to ensure that reliable contact had been established
between the lamination stack and the base plate.
presence of the external resin coating produced some problems,
particularly with the earth bond test. Because the earth
bond test is conducted to ensure the proper and secure
connection of the metal case to the mains earth reference
using test probes, each external metal surface must be
testeda process rendered nearly impossible by the polyester
challenges were involved in the development of a customized
solution to meet the quality assurance requirement for
fully integrated end-of-line testing. For example, testing
was to include checking both the electrical safety and
functional parameters of the product. To address this
particular challenge, the design team configured various
test modules into a dedicated system.
major hurdle, however, was to achieve successful testing
in a quick, simple, and operator-friendly manner. The
use of a safety enclosure is regarded as essential for
such applications for several reasons. It provides for
operator safety and ease of product location. It can also
be readily interfaced to the testing instruments for initiating
automatic sequencing of required tests.
fixturing that would automatically apply the test probes
to the various test pointslamination stack, mounting
plate, and ballast winding terminalsalso required careful
consideration given the nature of the product. For this
particular application, pneumatically driven test heads
were selected to provide the additional power required
for effective and reliable contact.
the base material of the laminations and mounting plate
was encased in a resilient, insulating, resin coating,
extensive research and experimentation were also required
to develop an optimal probe-tip design. The design had
to satisfy the criteria for making effective contact through
the resin to the base metal; moreover, it had to stand
up to the high-volume throughput of busy production cells.
features incorporated into the overall design were developed
to provide clear identification of faulty product through
audible and visual warnings. In addition, isolation of
all test outputs was achieved automatically whenever the
enclosure was opened.
end result was a fully integrated test and measurement
system that provides quick and simple testing of finished
ballast control products. Coupled with operator-safety
measures, this solution provided maximum production efficiency
at minimal unit cost.
Jansen is the vice president of test equipment manufacturer
Clare Instruments US Inc. (Tampa, FL). He can be reached