ehsjr wrote:
wrote:
ehsjr wrote:

wrote:

The L and the C don't care about your
DC offset, so you must still think of the signal as AC in order to
understand their behavior. They don't care that the overall signal
doesn't reverse polarity, they only care that derivative of voltage
with respect to time is non-zero.


Er - there are cases where the L will be saturated by
the DC component.

Ed

That's about the same as pointing out that some capacitors
are polarity sensitive, and will effectively be a short
if the polarity is wrong. It's true, but does not enter
into the problem at this point.

What you are suggesting is a good issue to keep in mind for
the real
world (and one I had overlooked).
However, what you have actually said is not true.
An inductance - a specific element we both referred to as L -
will not
saturate.

You mentioned the behavior of L and C, which refers to the

Inductors saturate. Inductance doesn't.

To me it is obvious that by L and C, he meant the inductance and
the capacitance, not the specific inductor or capacitor.

If he'd have meant a specific device, he have had to specify a
few parameters as to just what kind of a device, no?

way the *component* represented by C and the *component*
represented by L react. It is in your context that I used
the term L. Now, apparently, you have changed the context
to exclude consideration of the component (which will
sometimes lead to incorrect analysis) and to restrict the
term to have it refer to the property only. Therefore,
we did not refer to the same thing with the term L.

Exactly, except I don't think he changed the context.

What I referred to is a circuit element that can saturate, as per
the definition for inductance.

http://dictionary.reference.com/search?q=inductance
"1. The property of an electric circuit by which an
electromotive force is induced in it as the result of a changing
magnetic flux.
2. A circuit element, typically a conducting coil, in which
electromotive force is generated by electromagnetic induction."

A circuit element, not a component device.

snip

If asked to solve a problem with an inductance, you treat it
as such.
If asked to solve a problem with an inductor, you have to consider the
broader properties of that device, of which inductance is only one, and
not necesssarily a constant one.


I don't know where you came up with the above "rules" or whatever
you want to call them. If, in solving a problem with an inductance,
(specifically in this case, the effects of DC on an R,L,C load
impedance) no consideration is given to saturation, the solution
can be erroneous.

But saturation has nothing to do with the inductance. After the
right inductance is calculated, then a specific device has to be
chosen, and *that* is when saturation has to be considered. So
do physical size, mounting style, insulation, and perhaps other
parameters too, none of which are related to the original
"inductance" problem.

Very specifically for the op's question,
the possibility of saturation *must* be considered, even though
the question did not include the word inductor. I think those
rules, or whatever you call them, are not correct.

Could be! I don't remember the OP's question... :-)

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)