In message <[email protected]>, dated Sun, 10 Mar
2013, Ed Price <[email protected]> writes:
Indeed, that should be written on a wall in everbody's lab. Failures
don't always go the way we expect; everything that the product does
correctly has to be monitored for degradation, but beyond that, you
have to be aware of the possibilities of the unexpected. How far you
should continue down this dark tunnel of investigation depends on the
cost and consequences of device failures, and the limit of your budget,
paranoia and suspicion.
This is why 'risk assessment' was invented. But it is often
impracticably complex, so a simplified approach is necessary, which
might be 'overkill' but that is the penalty for simplification. If there
is a high enough degree of immunity to ALL single disturbances that can
occur in the product's environment with more than a minute probability,
the probability that more than one simultaneous disturbance causes a
malfunction is bound to be very small.
The key is to identify ALL single disturbances, and looking at the
relevant EMC standard is NOT sufficient. For example, most don't
consider the influence of magnetic fields.
A magnetic field is produced by EVERY current.
Transient currents, and therefore the magnetic fields they generate, can
be at least an order of magnitude larger than the steady-state current
in a circuit and its field strength.
A magnetic field induces a voltage into EVERY closed circuit, not just
into transformers and inductors.
--
OOO - Own Opinions Only. See www.jmwa.demon.co.uk
SHOCK HORROR! Dinosaur-like DNA found in chicken and turkey meals
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
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