17 Dec
2001
17 Dec
'01
1:21 p.m.
On Dec 17, 6:08, Richard Erlacher wrote:
I'm not absolutely sure about such things, but,
having had to sit through
the
annual ESD classes year after year in order to
maintain my cert's when I
was in
aerospace, ISTR that the "old" TTL was ESD
sensitive to a point, and I
seem to
remember something about TTL having a threshold of 2KV
for ESD
sensitivity.
That suggests that while it's not as likely to go
poof at the slightest
ESD, you
can't "ZAP" it without harming it.
Since the "ZAP" that you feel when
reaching
for the doorknob is >50KV, typically, the 2KV would
hardly be noticed.
That sounds about right to me. The instructor on my ESD classes in the
80's probably read the same books and data sheets that yours did. You
certainly wouldn't notice a few kV picked up by walking across a carpeted
room if it had a few seconds to dissipate before you touched something that
would discharge it instantly.
I remember one school who had a lot of BBC Microcomupters in the mid-80's.
All was well with them, until they had a building refurbishment, and the
micros wer moved to a new room with carpet tiles. They had endless trouble
after that, with machines resetting at odd times, misbehaving in unexpected
ways, and so on. When one finally stopped working altogether and I was
asked to look, I asked about the carpet. I suggested they mist it
periodically with well-diluted carpet cleaner to reduce static, and the
problems went away (I repaired the faulty machine -- it had a blown LS TTL
chip, which may or may not have been coincidence).
--
Pete Peter Turnbull
Network Manager
University of York