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Yokogawa WT1600 Digital Power Meter

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capt bullshot:
Collecting some posts from the TEA thread here, since this unit starts to get "interesting" - probably a teardown, fault analysis and (hopefully) repair will follow:

The Yokogawa WT1600: Typical Yokogawa knobs and button design. If you know their oscilloscopes, this should look familiar. The user manual found by your favourite internet seach engine reveals first rev. from 2001, this should approximate the date when the unit hit the market. It was discontinued ten years later in 2011 according to the Yokogawa website.



The cal sticker is dated 2010, so it'll be interesting to see how accurate this unit still is.



Alas, only one input element is fitted, and no other options.
For all the timenuts, the BNC labelled "EXT CLK" is not a 10MHz reference input, but rather an input to synchronize the unit to e.g. the fundamental frequency of measurement signals. Useful e.g. if you have quickly jumping amplitudes or heavily distorted signals. Normally the unit synchronizes its internal measurements to one of the input elements, U or I - one can select this through the menus.

capt bullshot:
Some early notes from the "Fun with (Ice)-TEA" dept.:

Trying to test the accuracy vs. bandwidth of the WT1600, starting with the voltage channel.
This thing has a quite impressive bandwidth / accuracy specification, so I wanted to see if I can set up some measurements to show this.
Starting with the Fluke calibrator, I've applied various DC voltages to check the basic DC accuracy. Looks well within spec.

Next thing is AC voltages. The Fluke can do from 50Hz up to 50kHz, at limited voltages (the higher the frequency, the lower the voltage). For 10V AC, covering the range from 50Hz to 50kHz it looks spot on, too.

Now for the more interesting part: I've set up the high speed amp. It can put out 50Vrms @ 1MHz, but unknown accuracy. So I'd need to measure these signals at a reasonable level of trust into my instruments. Turns out, this isn't that easy. The 34401A does a good job up to some 100kHz, and the scope shouldn't have any issues with the bandwidth at least.

So this is the setup I'm experimenting with now:



Fluke 5100B
33120A
34401A
NF 4005
RTB2004

I've got some other duties now, so stay tuned for more results tomorrow or maybe in the evening (CEST).

capt bullshot:
First results from todays "Fun with (Ice-) TEA dept.":

So I decided to use the 33120A and the amplifier as the signal source, and the RTB2004, HP34401A as meters for some plausibility checks.
The RTB2004 has a pretty nice feature, one can get its live screen onto a computer just by your favourite browser. The WT1600 has an VGA output that was captured with a grabber device. Finally the 34401A ouput was captured through a simple serial terminal.
This way I have all the interesting readings side by side on the computer screen.



I've started measuring at 100Hz, and stopped at 1.5MHz.
Each step I took a screenshot, like these:




Using human eye powered OCR, I've transferred the interesting measurements into a simple plain text file and made a small graph using gnuplot:




Below maybe 200kHz, I've used the 34401A reading to adjust the 33120A output level, above that the cycle RMS reading from the scope. The scope was connected through a standard 10:1 probe, whose gain error at low frequency (100Hz) was adjusted by fine tuning the scale factor. One can see, the probe isn't perfectly compensated, it drops at 1kHz and peaks at 100kHz a bit.
At the second screen shot (taken at 1.5MHz), one can see the amplifier is at its limits and starts distorting the waveform.
The WT1600 current channel shows 0mA at 100Hz, then 9.24mA at 1.5MHz - this is channel to channel crosstalk due to the high frequency.

capt bullshot:
Next measurement:
Fluke 5101B as source, 10V from DC to 50kHz:





HP34401A behaves as expected, with some dip in the frequency response at low frequencies. Best results around 1kHz.
WT1600 also behaves as expected, especially no (or very little) difference from DC to 50Hz. This is where the all digital signal processing and RMS calculation can show its capabilities. Basically, if you get your DC offset stable, you can adjust the measurement channel using a stable DC reference and it'll show accurate RMS values up to the bandwidth limits of the analog front end.
Interestingly, one can see the values drop until 10kHz, then showing a jump to higher values at 20kHz.

capt bullshot:
More WT1600 fun: Cough, cough "Husten, wir haben ein Problem" Edition (German dad joke pun)

Now testing the current measurement input, using the Fluke calibrator and the Tek current clamp:



This is the lowest range (10mA), with 10mArms applied:



100mA range:



This is the largest range (5A), 1.999Arms applied:



Doesn't give too much confidence into the measured values, does it?
Basically, the current measurement using the direct (shunt) input is off all over the place, with different offset and gain errors over the ranges. The unit has an BNC input for current measurement, this input looks OK on a first glance.

The block diagram doesn't give too much info of where the range switching happens in particular, so there'll be some teardown and fault analysis activity in the next days.

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