In The Trenches
example. (Although they do not apply
to consumer electrical products.)
All of this shows that the
responsibility to warn is important,
ethical, and, often, legal. If your product fails when it's cold, that should be
noted, not covered up. A risky "stan-dard design" is still risky and the users
should be warned. Examine the situation from the user's point of view. How
would you react to a failure? Would
your reaction be different if you discovered that information was withheld?
including the 1,000 volt version — are
the same price, according to
Digi-Key. (Other sources, like Mouser
and Jameco, may vary the price
slightly for the much higher voltages.)
So, if your power supply requires 35
volt rectifiers, why not use 100 volt
parts instead of 50 volt parts? This
example also raises a significant point.
It's important for you to know the
practical aspects of design. If you use
marginal parts, the design may fail. If
you use expensive parts, the design
may not sell. As always, the more you
know, the better you are able to design.
The better you design, the safer and
more reliable your product will be.
Finally, you should know the failure modes of your design. Your design
should "fail-safe." This fail-safe idea has
two parts. The first is that any single
failure should not cause the product to
be a danger to people or property. The
second is that a failure of one part
should not cause failures in other parts,
also known as a "cascade failure."
Fail-safe design requires the
engineer to understand the common
failures of basic parts. For example, will
the power diode most likely fail open or
shorted? What will be the result? Will a
signal diode fail in the same way? What
about capacitors and resistors? It's
much easier to consider these points as
you design the product, rather than
later. Get into the habit of looking for
problems. "Design Defensively."
To this point, we've discussed
personal safety. There is also the safety of property to consider. Obviously,
this is less important, but the concepts
of risk and safety apply here, too. You
want your product to operate well for a
long time. It's clear that failing products can easily lead to a failing company. It's also easy to see that safe
design and product quality are related.
Most often, poor designs fail for
the same reasons that accidents
happen: ignorance and/or stupidity.
An engineer working in a new area
makes mistakes because he doesn't
have the experience or an engineer
has done similar designs for so long
that he gets bored and ignores subtle
— but significant — variations. Good
engineering requires equal amounts
of common sense and attention to
detail. Know your limits.
If you are asked to do something
you don't think you are capable of, tell
your boss. Most likely, he'll appreciate
your honesty. On the other hand, he
will definitely not appreciate months of
floundering, followed by a product that
doesn't work. Your limitation might be
turned to your advantage; perhaps you
can take a course or go to a seminar.
That will enhance your capabilities;
learning new things is never a waste.
Use plenty of error margin when
designing. For example, the common
1N4001 rectifier diode has a reverse
voltage rating of 50 volts. The
1N4002 is rated at 100 volts; however,
the price is the same. In fact, in reels
of 5,500, all the 1N400X series —
Obviously, no one can be perfectly
safe all the time. No one can create a
completely harmless product; you
can always drop it on your toe or stick
it in your eye. Accidents will always
happen. Sometimes, it isn't your fault.
There's little you can do if a bridge
fails as you drive over it. Sometimes,
your actions attract an accident — like
playing golf during a lightning storm.
Safety and risk are important
everyday considerations for everyone. Generally, you are responsible
for your own safety. You decide if your
actions are safe or not. You decide to
wear safety equipment or not.
Engineers have special concerns. They
work with tools, machines, and electricity. They create products for others to
use. They decide how safe safe enough
is. These are responsibilities that
should always be taken seriously. NV
The Standard for checking
Good enough to be the
choice of Panasonic,
Pioneer, NBC, ABC, Ford,
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Locate shorted or leaky
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