Measuring power by Clamping

[woodzyspl]

too much, hurt brain

[Torres]

doubtful...or else i don't think he would have come up with the new tool

[TonyD'Amore]

I know what u are talking about I too have sat in a lab and played with pspice and know what a lagging verses leading cosines power wave looks like and how it affects output. You have to know power factor cosine theta to get just pavg and pint is not accurate either. Just trying to understand your view on how clamping is not power.

Excuse me if this is a little remedial for some, I want the less experienced to be able to understand it as well.

AMI, I totally understand your point. You are saying if you measure a woofer as 1 ohm DC resistance, and it rises to 3 ohms at some frequency because it becomes a reactive load, that is already in your math because you are measuring current directly. This is still VA though (apparent power), we would have to know the phase angle to convert to Watts (actual power). It is because the voltmeter is measuring average voltage and the current meter is measuring average current. The meters tell us the amplitude of the voltage and current, but not WHEN they are happening.

If we look at the picture attached, it is a simulated speaker being driven at 100V RMS. The green trace at the bottom of the picture is the voltage to the speaker, the red trace at the bottom of the picture is the current through the speaker. We can see the voltage going from +140Vac to -140Vac.. (a meter connected to this would read 100V RMS). Now we look at the red trace representing current, it is going from +101 amps to -101 amps... (a meter connected to this would read 71 amps AC). Using the "clamp math" we would say 100 x 71 = 7,100 (watts) but we know it's really 7,100 VA. We could also say this speaker is 1.41 ohms at this frequency by dividing the voltage by the current. However, notice that they are not perfectly in phase (the current peak and voltage peak aren't happening at the same time), so our math of 7,100 watts is incorrect. Notice the light blue trace at the top of the picture, this is the ACTUAL power to the speaker. It is calculated by measuring the voltage and current in real time and multiplying them (not multiplying the averages). The actual power can be seen as 5,750 Watts.

[TonyD'Amore]

I know what u are talking about I too have sat in a lab and played with pspice and know what a lagging verses leading cosines power wave looks like and how it affects output. You have to know power factor cosine theta to get just pavg and pint is not accurate either. Just trying to understand your view on how clamping is not power.

Excuse me if this is a little remedial for some, I want the less experienced to be able to understand it as well.

AMI, I totally understand your point. You are saying if you measure a woofer as 1 ohm DC resistance, and it rises to 3 ohms at some frequency because it becomes a reactive load, that is already in your math because you are measuring current directly. This is still VA though (apparent power), we would have to know the phase angle to convert to Watts (actual power). It is because the voltmeter is measuring average voltage and the current meter is measuring average current. The meters tell us the amplitude of the voltage and current, but not WHEN they are happening.

If we look at the picture attached, it is a simulated speaker being driven at 100V RMS. The green trace at the bottom of the picture is the voltage to the speaker, the red trace at the bottom of the picture is the current through the speaker. We can see the voltage going from +140Vac to -140Vac.. (a meter connected to this would read 100V RMS). Now we look at the red trace representing current, it is going from +101 amps to -101 amps... (a meter connected to this would read 71 amps AC). Using the "clamp math" we would say 100 x 71 = 7,100 (watts) but we know it's really 7,100 VA. We could also say this speaker is 1.41 ohms at this frequency by dividing the voltage by the current. However, notice that they are not perfectly in phase (the current peak and voltage peak aren't happening at the same time), so our math of 7,100 watts is incorrect. Notice the light blue trace at the top of the picture, this is the ACTUAL power to the speaker. It is calculated by measuring the voltage and current in real time and multiplying them (not multiplying the averages). The actual power can be seen as 5,750 Watts.

Direct link to image http://tinypic.com/r/35lvhb4/7

[will77530]

ok how do you measure the phase angle? and if you time v x a = watts where does the phase angle come into play. i may be making myself look like a complete moron right now but this is interesting and i want to know how it works

[TonyD'Amore]

ok how do you measure the phase angle? and if you time v x a = watts where does the phase angle come into play. i may be making myself look like a complete moron right now but this is interesting and i want to know how it works

You would have to use a 2 channel scope with a current probe to look at the voltage and current at the same time. If you were using one of the "smart scopes" it would probably be able to tell you the difference in phase. In the example I posted above the voltage and current are about 36 degrees out of phase. Then Cosine (36 deg) = Power Factor 81%. 7,100 VA * 81% PF = 5,750 WATTS

[Real96SS]

Can we get another cool demo video explaining this while you demostrate it? You guys have already done videos testing amps on the AD-1 so why not just clamp those same amps the way everybody has been doing to show us the difference between that and the AD-1 Amp Dyno?

[will77530]

ok how do you measure the phase angle? and if you time v x a = watts where does the phase angle come into play. i may be making myself look like a complete moron right now but this is interesting and i want to know how it works

You would have to use a 2 channel scope with a current probe to look at the voltage and current at the same time. If you were using one of the "smart scopes" it would probably be able to tell you the difference in phase. In the example I posted above the voltage and current are about 36 degrees out of phase. Then Cosine (36 deg) = Power Factor 81%. 7,100 VA * 81% PF = 5,750 WATTS

one last question and i think im good how do you know the cosine of 36 deg = a power factor of 81 percent

[armykyle1]

very interesting! Still kind of confusing though. So the clamp method won't work even if you're not using a reactive load? It sucks that method isn't accurate...

[ChevyBoy95]

very interesting! Still kind of confusing though. So the clamp method won't work even if you're not using a reactive load? It sucks that method isn't accurate...

clamp method now seems to be