I likely used the same current probe that Ed did ­ the Pearson Model 3525 ­
because it is flat from 10 Hz to 10 MHz, I assumed that it would be flat in
phase as well, but I didn¹t know if there was a fixed shift or not, so I
measured that and it was 0 degree phase shift, so I could do what Ed did.

Ken Javor
Phone: (256) 650-5261



From: Edward Price <e...@jwjelp.com>
Reply-To: Edward Price <e...@jwjelp.com>
Date: Tue, 13 Feb 2018 11:51:29 +0000
To: <EMC-PSTC@LISTSERV.IEEE.ORG>
Conversation: [PSES] Current measurement
Subject: Re: [PSES] Current measurement

I had to measure inrush power and power during some function switching. I
had a really nice 4 channel digital oscilloscope with math functions, so
here¹s what I did.
 
1.  I put a 10x voltage probe on Channel 1 and verified the the probe
factor.

2.  I put a 1x Pearson current probe (very flat response up through 10 MHz)
on Channel 2 and verified the probe factor.

3.  I chose the waveform math to multiply Channel 1 times Channel 2 and
display this in Channel 3. This gave me Vrms displayed on Channel 1, Arms on
Channel 2, and real time Watts RMS displayed on Channel 3.

4.  I could then use the MAX & MIN cursor functions to find the highest
power draw anywhere along that power waveform.

 
I was able to trigger off the Channel 1 Voltage, but I could have triggered
on the current or even used an external trigger. Plotting the Power waveform
was really interesting.
 
Ed Price
WB6WSN
Chula Vista, CA USA
-----Original Message-----
From: Ken Javor [mailto:ken.ja...@emccompliance.com]
Sent: Monday, February 12, 2018 1:09 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Current measurement
 
Unless you can look at both voltage and current on an o'scope and compute
phase angle between them, you are only measuring apparent power.
 
Ken Javor
Phone: (256) 650-5261
 
 
 
> From: Amund Westin <am...@westin-emission.no <mailto:am...@westin-emission.no>
>
> Reply-To: Amund Westin <am...@westin-emission.no
<mailto:am...@westin-emission.no> >
> Date: Mon, 12 Feb 2018 22:04:44 +0100
> To: <EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> >
> Subject: [PSES] Current measurement
> 
> If you want to calculate the consumed power (W) in a 1-phase AC
> circuit, you can use a current clamp-on device to measure the current
> in one lead/wire and multiply with the applied voltage.
> But with such a current clamp on device, to we measure the apparent
> power
> (VA) or the real power (W)?
> 
> Best regards
> Amund
> 
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