On Fri, 10 Jun 2005 22:53:35 -0700, jackbruce9999 wrote:

I will absolutely buy what you said, but understand the import of what
you're saying....you're saying that the language of "AC" and "DC" has
essentially been somewhat *******ized from its original meanings to
also mean zero-frequency and non-zero-frequency signals. Therefore, to
describe a 10Vpp signal with a 10VDC offset as an "AC" signal is
actually contrary to the original connation of "alternating current"
since it (net) results in a signal which yields only a mono-directional
(i.e. direct) current flow (albeit time variant). So in a sense, you
could say I am holding "pure" to the original (circa 1890's) definition
of AC/DC while its use has been "officially" corrupted to cover the
concepts of "zero frequency" and "non-zero-freuency".

Agree?

I can't vouch for the historical facts, but as far as zero frequency and
non-zero-frequency goes, you are pretty much correct.

Another point to note is that many signals have both AC and DC. It is
not a dichotomy. The signal you mentioned at the start of this thread has
both AC and DC.

Historically, I think what happened is that the terms originally were used
to describe two competing power sources (the war between those who wanted
a DC power grid and those who wanted an AC power grid was surprisingly
fierce). Later, the terms started getting used to describe signals, and
that is probably when the shift to the ZF- and NZF-meaning happened.

Also, there may be people out there who still think of AC and DC in the
original sense (I'm not sure about this, but maybe people who work with
power stuff exclusively), but among electrical engineers, the signal
perspective prevails.

--Mac