Re: On the Concertina phase inverter controversy

On Wed, 20 Aug 2008 13:12:29 -0500, John Byrns <byrnsj@xxxxxxxxxxxxx>
wrote:

Hi Rodger,

Great post. Could you elaborate on the IEEE definition of "driving point
impedance"? I don't understand how you can measure any "impedance at a single
node" of a circuit; obviously there is an implied reference node involved in the
measurement. I am curious how the IEEE defines and restricts our choice of this
reference node?

The reference node is indeed implied, but it's up to the person making the
measurement to pick an appropriate reference node. All measurements and
stimuli are with respect to this reference node. The IEEE doesn't say
anything about restrictions.

The driving point impedance is defined like this: inject a current into a
single node (call it node A) with respect to a "reference" node. Measure
the voltage at node A resulting from the injection of current. Divide the
resulting voltage by the stimulus current. This is the driving point
impedance.

There is also transfer impedance (and the related parameter, transfer
conductance, or transconductance), which is the ratio of the voltage at
another node with respect to the current injected at the first node.

Differential impedance would be measured (or calculated) by injecting a
current, i, into node A while simultaneously extracting the same current
from node B (this is what would happen if a small handheld LCR meter were
connected between node A and node B). Measure the voltages induced at node
A, v(A), and node B, v(B), with respect to the reference node. Calculate
(v(A)-v(B))/i; this is the differential impedance between node A and node
B.

In real hardware, of course, the reference node will almost always be the
circuit "ground" which is often a metallic enclosure, or other metallic
bonding point.

Interestingly, it is useful to analyze networks without using one node as a
reference. Jacob Shekel published a paper on this topic in Wireless
Engineer in January 1954. He starts out his paper by saying:

"When a network is analysed by nodal equations, it is necessary to choose
one of its nodes as a reference node, and all the other nodes are measured
(or defined) relative to this special node."

He then says:

"This paper...proposes a method of treating networks without specifying the
reference node at all."

He calls the admittance matrix for a network without a reference node, the
"indefinite" admittance matrix.

I haven't scanned his paper, but I have scanned a more recent paper that
explains the method. I've posted it again over on
alt.binaries.schematics.electronic.

It's titled "Unify two-port calculations".
.

Relevant Pages

  • Re: On the Concertina phase inverter controversy
    ... Could you elaborate on the IEEE definition of "driving point ... I don't understand how you can measure any "impedance at a ... obviously there is an implied reference node involved in ... I've posted a second paper on indefinite admittance matrices over on ABSE. ...
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  • Re: On the Concertina phase inverter controversy
    ... Could you elaborate on the IEEE definition of "driving point ... I don't understand how you can measure any "impedance at a single ... obviously there is an implied reference node involved in the ...
    (rec.audio.tubes)