Accurately Measuring RMS current into 230VAC xenon flashlamp?

[treez]

Hello,

We wish to measure the RMS current drawn by a 10W xenon flashlamp that runs on 230VAC (flash rate is 1.5Hz.

We have used Fluke 179 to do this......Its a true rms meter, but we are not sure how accurate it will be.
The input stage is a series capacitor dropper and a mains rectifier bridge.

Fluke 179
http://assets.fluke.com/manuals/175_____umeng0100.pdf

I wonder if we should put a series current sense resistor after the rectifier bridge and measure the voltage across it with TDS210 scope?....we can then get an idea of the crest factor and amount of distortion in the input current waveform...so that we can see if the FLUKE 179 will be accurate.

Maybe we will need to buy a WT210 power meter to get accurate measurements in this application?

WT210 power meter
**broken link removed**

I take it that the Fluke 77 meter would be very inaccurate because its an averaging type meter?

Fluke 77
**broken link removed**

 

[FvM]

Before discussing instrument details, you need to define the measurement quantity of interest. It's not obvious due to the pulsating input current.

 

[treez]

RMS input current is what i am interested in

 

[nagendra.singh]

you use current probe from Tektronix to measure accurate current.

 

[FvM]

RMS input current is what i am interested in

Obviously that's in the question title.

But there's a time constant respectively averaging intervall involved with RMS definition. How do you set it? Do you record a varying short time average or averaging over full flash periods? Can it be that you didn't think about the question?

P.S.: If the the measurement is somehow related to power quality regulations, we would refer to the 1.5 s time constant for harmonic current determination specified in IEC 1000-3-2 as a first guess.

 

[treez]

FvM:

Regarding the averaging interval, .....we are simply using the Fluke 179 at the moment......and it is giving us a reading.

I see what you mean because the averaging interval in our case should be about 0.67 seconds....and this is a long time in electronics as you know......i am wondering how the fluke 179 works out that the period is 0.67 seconds?

Do you think our Fluke 179 meter is going to be very inaccurate?

I think i may need to get out our TDS210 scope and place a current sense resistor after the mains rectifier and have a look at the current waveform shape........the thing is, the TDS210 will not be able to calculate the crest factor of the waveform, so im still going to be wondering how best to measure this waveform even if i do use the scope to view it.

 

[FvM]

The quantity of interest question hasn't be clarified, I fear. A RMS meter like the 179 will giv eyou a time varying measurement, so what's the correct RMS current number?

Average RMS current would be a clear specification. But you have been also talking about distortion and crest factor, which are time varying, too.