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### Author Topic: Power Measurement Basics  (Read 28202 times)

#### MarkE

• Hero Member
• Posts: 6830
##### Re: Power Measurement Basics
« Reply #15 on: January 20, 2014, 09:51:10 PM »
You've re-stated basically what the diagram is depicting, but how did you come to the conclusion that the battery dissipates -10W, or the resistor +10W?

Why did you not conclude that the battery was dissipating +10W and the resisitor -10W?
There are two possible conventions.  Either works mathematically provided one applies it consistently.  I chose the convention used throughout industry and academia.

#### Free Energy | searching for free energy and discussing free energy

##### Re: Power Measurement Basics
« Reply #15 on: January 20, 2014, 09:51:10 PM »

#### poynt99

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• Posts: 3585
##### Re: Power Measurement Basics
« Reply #16 on: January 20, 2014, 10:40:00 PM »
There are two possible conventions.  Either works mathematically provided one applies it consistently.  I chose the convention used throughout industry and academia.

Would you mind showing your calculations?

#### poynt99

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##### Re: Power Measurement Basics
« Reply #17 on: January 20, 2014, 10:42:52 PM »
They do not oppose.  Both probes are in phase.  In order to oppose one must be CCW and the other CW from the reference node.
Please show diagrammatically what you mean.

#### Free Energy | searching for free energy and discussing free energy

##### Re: Power Measurement Basics
« Reply #17 on: January 20, 2014, 10:42:52 PM »

#### poynt99

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##### Re: Power Measurement Basics
« Reply #18 on: January 20, 2014, 10:51:47 PM »
Which is the reason that I object to your choice of positive power as that supplied by a source when the common convention for positive power is the quantity dissipated by loads.

Mark, please quote me where I stated that a measured source power computes to a positive value.

Quote
If one is intent on educating folks, which is a good thing, teaching them to go against accepted conventions is a recipe for confusion and dissent.
Agreed, which is why I'm continuing with this discussion.

#### MarkE

• Hero Member
• Posts: 6830
##### Re: Power Measurement Basics
« Reply #19 on: January 20, 2014, 11:00:02 PM »
Would you mind showing your calculations?
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
Source positive terminal / load top Node 2

Vcsr = V1

#### Free Energy | searching for free energy and discussing free energy

##### Re: Power Measurement Basics
« Reply #19 on: January 20, 2014, 11:00:02 PM »

#### MarkE

• Hero Member
• Posts: 6830
##### Re: Power Measurement Basics
« Reply #20 on: January 20, 2014, 11:26:48 PM »

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

• Hero Member
• Posts: 6830
##### Re: Power Measurement Basics
« Reply #21 on: January 20, 2014, 11:37:36 PM »
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.

#### Free Energy | searching for free energy and discussing free energy

##### Re: Power Measurement Basics
« Reply #21 on: January 20, 2014, 11:37:36 PM »

#### poynt99

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##### Re: Power Measurement Basics
« Reply #22 on: January 21, 2014, 12:45:21 AM »
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

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##### Re: Power Measurement Basics
« Reply #23 on: January 21, 2014, 01:54:17 AM »
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
Source positive terminal / load top Node 2

Vcsr = V1

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?

#### Free Energy | searching for free energy and discussing free energy

##### Re: Power Measurement Basics
« Reply #23 on: January 21, 2014, 01:54:17 AM »

#### poynt99

• TPU-Elite
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• Posts: 3585
##### Re: Power Measurement Basics
« Reply #24 on: January 21, 2014, 02:03:37 AM »
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.

#### gotoluc

• elite_member
• Hero Member
• Posts: 3096
##### Re: Power Measurement Basics
« Reply #25 on: January 21, 2014, 03:06:51 AM »
Hi poynt,

just noticed this topic. Glad you're making these much needed video demo's

I've noticed MarkE scope shot has AC coupling selected on channel 2. Is this not an issue?

Thanks for all your work to make this happen. I'm sure over time you'll get much appreciation for doing this and in the long run you'll save time on explaining to different individuals like me

Looking forward to the show

Luc

#### Free Energy | searching for free energy and discussing free energy

##### Re: Power Measurement Basics
« Reply #25 on: January 21, 2014, 03:06:51 AM »

#### poynt99

• TPU-Elite
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• Posts: 3585
##### Re: Power Measurement Basics
« Reply #26 on: January 21, 2014, 03:09:42 AM »
OK, the video is now assembled in the right order. It should make sense now. Here are the links to both parts.

Sorry for the inconvenience.

#### MarkE

• Hero Member
• Posts: 6830
##### Re: Power Measurement Basics
« Reply #27 on: January 21, 2014, 03:14:31 AM »
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?
This is getting extremely tiresome.  I have diagrammed, I have provided equations, I have explained, and explained and explained and there seems to be zero progress in our communications.  I suggest that you do any of the following:

1. Pick up a text on power engineering.
2. Search the topic of power sign convention in Google.
3. Look at any of the many, many, many references for electrical power convention

You will find that we determine:

In any circuit branch where the positive convention current flow is in the direction of more positive towards less positive voltage drop that circuit branch is absorbing power, and the sign convention for the measured power is positive.  In any circuit branch where the positive convention current flow is against the direction of more positive towards less positive voltage drop that the circuit branch is emitting power, and the convention for the measured power is negative.  IE:  Absorbed / dissipated power is by universally accepted convention positive power, and supplied power is by universally accepted convention negative power just as in the figure below that you keep questioning.

Surely you acknowledge that P = V*I including signs.
Surely from executing any of the above checks you will find that the industry and academic convention for power sign is positive for circuit branches that absorb power, IE are loads and is negative for circuit branches that supply power, IE are sources.
Surely you can observe from your videos that what you did was measure and record negative voltages across each of your loads as you moved your measurements around in the direction of current flow.
Surely you can observe from your videos that multiplying the voltages you measured across each of your loads against the currents yields negative power values.
Surely you can see that by doing that you are going against the power sign convention used by industry and academia.
Surely you can can see that when you finally worked your way around to where you had a probe on the circuit common, the probe that you had there was the red lead, when common practice is to place the black lead there.
Surely you can see that placing the black lead where your audience and 99.99% of the rest of the world places their black leads is going to cause confusion for your audience.
Surely you can see that this is not going to make it easier for people to understand the usefulness of your technique of moving the measurement common from the power source common to the junction of a current sense resistor and the low side of the circuit under test.
Surely, when you tell your audience that you have to invert the current sense scope channel when using your perfectly valid technique you can understand that they may very well continue to protest against that absolutely correct measure due to confusion you are aggravating.
Surely since your goal is to get your audience to understand how to accurately account for the direction of power flow in their circuits, particularly when that direction varies with time, you agree that it is important that you reduce rather than increase the confusion any of your audience may suffer.

I am totally at a loss as to why we are not communicating.  I know that you are a capable engineer.

#### MarkE

• Hero Member
• Posts: 6830
##### Re: Power Measurement Basics
« Reply #28 on: January 21, 2014, 03:22:57 AM »
Hi poynt,

just noticed this topic. Glad you're making these much needed video demo's

I've noticed MarkE scope shot has AC coupling selected on channel 2. Is this not an issue?

Thanks for all your work to make this happen. I'm sure over time you'll get much appreciation for doing this and in the long run you'll save time on explaining to different individuals like me

Looking forward to the show

Luc
Gotoluc, no it is not an issue at all.  AC coupling does not invert phase.  AC coupling removes information from below the cut off frequency.  In this case the probe has a cut off frequency of about 350Hz and the oscilloscope has a cut off frequency of about 5Hz.  The source signal is a clean 10kHz sine wave and has virtually no energy below 10kHz.  If the signal had a DC offset in it, the AC coupling would have removed that offset, shifting the signal up or down towards an average voltage of zero.

#### poynt99

• TPU-Elite
• Hero Member
• Posts: 3585
##### Re: Power Measurement Basics
« Reply #29 on: January 21, 2014, 03:31:04 AM »
Luc,

The AC coupling shown there is no problem. Mark is using a real current probe. The P6021A is only good down to 120Hz, so it would not be suitable for your AC measurements.