COP 20.00 (2000%) Times, Reactive Power Energy Source Generator,

[listener191]

All,

Attached are  prints from a Rigol DS1104Z scope, which has a Math function. A differential probe was used for the voltage measurement and a clamp for current. You can see the RMS values displayed for voltage and current and the AxB function is used to display Watts (peak). So far I have not found a way to apply an RMS value to the Math function.

The shot with in phase V & I is the load.

Barry

[TinselKoala]

Nice displays. The scope is pretty smart: when you are using a current probe it displays in Amps and when it sees that you are multiplying Amps x Volts it gives you the result in Watts. But why would you want to apply RMS to an instantaneous power trace?  "RMS Watts" really has no physical meaning. It is the _average_ Watts value, not RMS, that represents actual dissipated power over a time interval.

When using active differential voltage probe and current clamp probe, the probes will have slight time delays. This will cause phase angle errors which in turn will affect the instantaneous power calculation. This problem is generally called "probe skew" and many advanced scopes have a probe de-skewing menu and options to correct for these time delays. Here's a short article from Tektronix talking about the issue with their scopes and probes.

http://www.newark.com/pdfs/techarticles/tektronix/Probing_power_measuremets.pdf

[Farmhand]

All,

Attached are  prints from a Rigol DS1104Z scope, which has a Math function. A differential probe was used for the voltage measurement and a clamp for current. You can see the RMS values displayed for voltage and current and the AxB function is used to display Watts (peak). So far I have not found a way to apply an RMS value to the Math function.

The shot with in phase V & I is the load.

Barry

I think the questions most folks might be wanting to ask are.

1) What was the input power from the wall socket and the power factor there ?

2) What was the output power, or what was the power consumed by the bulbs ?

Those figures would allow folks to gauge to some degree what is going on.

eg. if at the wall socket the power factor is bad and VA and VAR are high compared to Watts in, and Watts in are more than
watts consumed then we could roughly determine the effect and magnitude of VAR at the socket.

I find it difficult to believe that a person would do all that setup and experiment without determining the input and power factor
from the wall socket at the wall socket, and therefore already have a figure of some kind for efficiency, apparent and real powers.

Where was the setup probed for the shots ?

..

[listener191]

This is exactly the same setup as before with the Owon scope.

The out of phase V&I waveforms were at the input from the source (secondary of transformer). The in phase waveforms were taken across the load.

Farmhand mentioned this before, and by comparing with a voltage sample across a shunt resistor, I demonstrated that the current clamp does not have skew.

The RMS function was applied to the measurements at the bottom of the display for comparison with an energy monitor that is at the input.

The Math function AXB, is a sample by sample calculation and is displaying the power waveforms.

Barry

[listener191]

Regarding the differential probe. I will check the skew against a grounded probe, but the V I phase looks the same as the previous waveforms taken on the Owon scope.

The reason for the differential probe is so I can measure anywhere in the switching circuit, without probe reference issues.

Barry