Products > Test Equipment
Yokogawa WT1600 Digital Power Meter
capt bullshot:
Next one, the WT1600 vs. the Voltech PM3300:
capt bullshot:
Last, but not least: WT1600 vs. Tek A6302 plus AM503 and RTB2004 Math and Measurement features:
Note:
The NF 4005 amplifier has a specified frequency response to 1MHz, so one has to expect more or less relevant phase errors at frequencies above maybe 200kHz. So I don't know wether the -0.7W deviation at the end of the frequency axis (800kHz) is caused by the power meter or by the amplifier / dummy load.
At least all the power meters agree to some degree, so this points to the amplifier causing the phase shift, otherwise the Tek current probe and the scope should have enough bandwidth to not cause a significant error here. I haven't investigated why the phase shift at this combo is into the other direction (positive real power displayed instead of negative).
I've deskewed the current probe vs, the voltage channel, so I'd put some trust into the scope measurement, otherwise it's the only measurement that largely disagrees with the power meters ...
So no idea ATM which one is more correct.
Edit / P.S.: Now that I'm looking at the finished post, it's quite obvious I did the deskewing wrong, leading to a phase lead at the current probe / scope setup. So it's this last measurement that's lest trustworthy.
capt bullshot:
Rinse and repeat friday:
Did the above measurement again, with proper deskew. Now it looks plausible:
Anyway, let's face it: It's rather difficult to properly test these high bandwidth power meters vs. their specifications (TBH, I can't be bothered to compare my results to the actual specs right now). It looks plausible, and I'd trust Yokogawa to keep their specs, while the Voltech specs might be rather optimistic (at least as far as I remember).
_Wim_:
--- Quote from: capt bullshot on May 19, 2022, 07:01:49 pm ---Next one, the WT1600 vs. the Voltech PM3300:
--- End quote ---
Very interesting tests! This makes we want to buy such a high speed amplifier, but prices on Ebay are :o
I am not sure how these power meters manage to measure up to 1 MHz. As far as I can see, the Voltech has a max sample rate of 333KHz, and the Yokogawa of only 200kHz. As both units measure voltage and current directly and do all calculations in the digital domain, this would mean they use some sort of equivalent time sampling making use of the repetitive signal. Or do they use another trick?
I have a Voltech PM6000, but never actually did such extensive testing. Maybe I also give this a try in the future when I find some time for it...
capt bullshot:
Regarding the sampling frequency / bandwidth: There's no trick at all, it just works by the nature of the matter :)
For calculating the basic values (Urms, Irms, P), the signal frequency isn't of concern at all. One just integrates over an integer multiple of the period time, no matter what the actual signal or sampling frequency is.
It's some kind of ETS, though it's not necessary to reconstruct the waveform as the sampling oscilloscopes do.
For example, in the frequency domain, a 300kHz signal gets aliased to 100kHz if a sampling rate of 200kHz is used. For Urms / Irms / real P computation it doesn't matter wether the original signal @300kHz or the aliased signal @100kHz is seen by the calculation, as long as both (U and I) signals undergo the same conversion and keep their phase relationship.
There's one corner case: a signal frequency of an exact integer multiple (including 1) of the sampling frequency gets aliased to DC, this can lead to large errors or at least confusion. Didn't check this with the Yokogawa, but I've seen instruments avoiding this by changing the sampling frequency slightly (afair the Clarke Hess does so).
The WT1600 has a harmonics analysis mode, too. Here's the whole thing a bit different: As you want to apply (usually) a FFT with rectangular window to the input signal, the sampling frequency gets synchronized to the signal frequency by means of a PLL circuit (At least this is my guess from reading the manual). This mode is quite limited in terms of fundamental frequency, maybe max. 1kHz afair. Usually you want to switch an aliasing filter into the signal path to avoid the aliasing here.
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