DC Power and Energy Pt2

[Zhang]

Hi Martin,
I find your video very exciting. You show in your video, such as the voltage under load decreases at Porta Power. You explain it with the 3-point measurement in the device. Better would be a four-point measurement, but how do I make such a 4-point measurement?

Right now I have the exact problem with my Dummylload, I think
http://mjlorton.com/forum/index.php?topic=626.0

I have read on the internet about 4-wire measurements but at the moment I still do not understand the context.
How do I implement such a 4-point measurement in a circuit?

Maybe someone can explain it. In an example maybe?

Thanks for the help

Zh4ng

[TechJunkie]

There are several ways you can do this.

1) Buy a 4-wire meter. 

2) If you have 2 DMM's, you can use one to measure the current and the other to measure the voltage drop across the load and then use Ohms law to get power.

3) Use the above method with a known precision shunt resistor value.

If you want to get variable power usage and total, you can use data logging software and import this into a spreadsheet then perform the calculation for power at each point to get the total power. It take a bit of math but not too hard. The faster the sample rate the better accuracy you will have.

If I get more time later today, I can detail the process a bit more.

[Zhang]

Hello TechJunkie,

Thanks for your reply. Kelvin Clamps are ordered.

How can I implement in a 4-point measurement in a circuit? At the moment I do this via a simple voltage divider.

thx
Zh4ng