Us OLD guys used to think that digital was two levels of voltage - back
then +5VDC and 0VDC.
Thus DC could also mean Digital Computers. Way back then, the things did
run relatively slow compared to these days so the AC signal you think of
was only the step function of getting from one level to the next. In fact,
we used to do that with switches on the front panel - manual clocks. These
days, DC step functions happen faster than the settling time, leading to
the appearance of AC looking signals.
- Bill
At 05:53 PM 11/07/2001 , eric.lif...@ni.com wrote:
A question was posed as to when a digital I/O signal can be treated as a DC
voltage source. My reaction is it must be treated as a AC signal.
However, it could be operated such that the output changes state rather
slowly. (This is a simple programmable I/O port for most any use.) But,
the concept and some digging led me to another question.
I consulted two UL standards: 508C and 3121-1 (and it's kin 3101/3111-1,
all based on IEC 61010-1), both led me (by reference) to UL 1310 Class 2
Power Units. UL 1310 has a clause (14.2.2) which indicates that a "DC
interrupted at a rate of 200 Hz or less" is limited to 24.8 V peak. In the
same clause it mentions a "continuous" DC voltage of 60 V DC is
permissible.
To my knowledge, "a rate of 200 Hz or less" is explicitly saying that any
interruption in power, even to shut it down on occasion, invokes the 28.4 V
DC limit. (Silly interpretation, but that's what it says.)
So friends, how continuous must DC be to qualify as continuous DC?
Best Regards,
Eric Lifsey
Compliance Manager
National Instruments
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British Prime Minister Tony Blair pointed to the victims of the Sept. 11
attacks on the World Trade Center and the Pentagon, and said the Taliban
regime had no "moral inhibition" on slaughtering innocent people.
"There is no compromise possible with such people, no meeting of minds, no
point of understanding with
such terror," he said. "There is just a choice: Defeat it or be defeated by
it and defeat it we must."
"Whatever the dangers of the action we take, the dangers of inaction are
far, far greater," he said.
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919) 392-8341
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