Problems measuring the average power with Picoscope

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Problems measuring the average power with Picoscope

Post by ginger » Tue Apr 29, 2014 10:05 am

Hi there,

I´m trying to measure the average power on the secondary site of an power Transformator using Picoscope.

This is a Picture of my measurement:

The voltage V(t) is displayed as blue graph, the electrical current I(t) is displayed as red graph.
I´m using an advanced Trigger, so that the there is no jitter.
I´m also using a time ruler to measure only two periods of my signal.
I´m using a "Math Channel" to calculate the "Instantaneous power", a simply Multiplication of V(t) and I(t), which is displayed as green graph.

So far I didnt have any Problems, but now as I want to measure the average power, I have some Problems.

I do now want to measure the average Power.
The average power is easy to calculate, it is the integral of the instantaneous power over the desired period of time.
I´m using a new math channel for the average power, using the formula " 10500*integral(V(t)*I(t)) ". The factor 10500 is correct. So far, so good.
Now I´m adding an measurement. I do select the math channel "average power", I do select the section of the graph between the rulers (in this case two periods of my signal). But I´m not certain which type of measurment I should choose.
I did measure "Maximum", "AC RMS", "True-RMS" and "DC Average" in four measurements (as you can see in the Picture). But now I completly unsure which of this measurments does tell me my average power.

I´m pretty confused, because acutally I just want to know the solution of my integral, it´s a simple mathematical Operation. But I have to choose a "type of measurement" and I´m not sure which Option I should choose, the Programm is a Kind of black box for me at this Point.

Who could I ask for more Information?

Kind Regards

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Re: Problems measuring the average power with Picoscope

Post by Jeff » Thu May 01, 2014 3:26 pm

Hi Ginger,

We have an application note on this subject: ... lysis.html.

The short answer is that you don't need to integrate, you just take the DC Average measurement of your green channel. The DC Average measurement contains an implied integration, so you don't need to do it again.

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