Power Measurement Basics

[MarkE]

Mark, please quote me where I stated that a measured source power computes to a positive value.
Agreed, which is why I'm continuing with this discussion.

That falls out of a consequence of your procedure that amounts to measuring the voltage rail and the current through the load as your source power.  As I have read your posts you seem quite adamant that you are measuring the source power with that method.  For the positive polarity power supply, both the voltage measured and the positive convention current are positive.  Therefore their product: the measured power is positive.

[MarkE]

Please show diagrammatically what you mean.

I already have.  See once again the diagram on the left, and the diagram on the right.  On the left, moving from node zero to either measurement point is CCW.  On the right, moving from node zero to the voltage measurement point is CCW and the proxy for the current measurement, the CSR voltage the direction is CW.  A common loop current circulating in either direction develops voltage measurements of opposing signs on the two channels.

The diagram on the left is the accepted and vastly predominant method of measuring voltage and currents in a circuit.  If one models a non-contact current sensor, a transformer primary replaces the CSR.  The transformer imposes a small series voltage burden to AC just like the CSR does at all frequencies.

[poynt99]

I just realized that the order of the individual parts of my video are all messed up. I will have to re-assemble and upload them again.

[poynt99]

Take the test case I offered driving a 1 Ohm load with a series 1 mOhm CSR.  Use the diagram of that I posted.  We are assuming lossless wiring and no hidden circuit elements:

Label the nodes:  Source negative terminal / CSR bottom Node 0
CSR / load Node 1
Source positive terminal / load top Node 2

Vload = V2 - V1
Vcsr = V1
Iloop = V2/(Rload + Rcsr)
Pload = (V2^2 - V2*V1) / (Rload + Rcsr)

Since Rcsr << Rload, then Rload ~= Rload + Rcsr and V2 ~= V2 - V1, then Pload ~= V2*V1/Rcsr

I have no problem with this method of measuring the load power, because it works. However, it is NOT in the purest theoretical sense the ideal way to perform it. We do it this way because it is practical for most of us.

What remains is an explanation as to why or how you can conclude that the source dissipation is negative. Do your calculations work out there?

[poynt99]

That falls out of a consequence of your procedure that amounts to measuring the voltage rail and the current through the load as your source power.  As I have read your posts you seem quite adamant that you are measuring the source power with that method.  For the positive polarity power supply, both the voltage measured and the positive convention current are positive.  Therefore their product: the measured power is positive.

Strictly speaking yes, if you are measuring directly across the battery, you are measuring battery power. If you are measuring directly across the load resistor, you are measuring the load resistor power.

We can "cheat" however to obtain the load power without measuring directly across it, as has been outlined already here. It is a "cheat" because the two voltage measurements are effectively in parallel or pseudo-difference mode. As such, this only works for measuring the load power.

The problem here as I see it is perception. I see the circuit as one continuous loop and you seem to see the circuit as two half loops, one CW and one CCW, using the reference point as, well, a reference. To be honest, I do not understand your explanation regarding the relevance ofCW and CCW in your above post. There is also the issue of performing a measurement a certain way because we have no choice, and a certain other way because that is the ideal way.

At any rate, no I do not ever state nor imply that loads compute to a negative power. In fact I state quite clearly in the video that sources always compute to a negative value.