121GW VA-Mode Problem & Solution

The suggested connection of the 121GW in VA-mode ignores the burden-voltage and compromises the stated 1% accuracy.
Watch to find out about the clever solution to get the full accuracy back without any further maths, additional components etc. :-)
Firmware version in this video: V1.57

[jeffbenshetler]

I have this meter and need to measure mW power ranges today. This is a great help. Thank you.

[nethoncho]

Roger, that is ingenious. Thanks to you and Joe Smith

[SIXSTRING]

Great video. I've watched about every video Joe Smith has out there and not surprised he found this problem and solution. IMHO he has the best electronics problem solving and re-designing skills of multi-meters and test equipment out there. I don't know what his background is or job but obviously it's pretty deep in electronics as well as mechanical skill. I've mentioned to him on a few occasions he should be doing design work for some big test equipment company. I'm pretty novice to the electronics game, but his videos have influenced my past 4 multi-meter purchases just because of his thorough in depth videos of tear downs and testing. I love the Brymen meters to which I would have never heard of until finding Joe's channel. Once again great video breakdown of Joe's solution.

[orionsmith]

Nice hack. Thanks to both you and Joe for pointing this out and the reasoning behind it.

[station]

Ah yes, the curse of common ground in instrumentation.
It's a nice work around.
Could you repeat the experiment with a bench supply in the shot ?
Would show visually what current/voltage is going into the circuit, with and without the 121GW in circuit.

[movaxh]

Depends what you are measuring. I use this method for very long time for measuring the power consumption by the load. But sometimes you want to instead measure power delivered by power supply. Then you actually want to include the burden voltage, and power dissipated in shunt resistor. I wasn't aware it is not well know fact.

[stuartmp]

Really nice. Thanks you for posting such a through video

[boonedockjourneyman]

Great stuff. Is that RCL box a commercial product? It would clear a bunch of space on my bench.

[joegennaro]

Hi Rodger would this solution work on the Dave Jones BM 235 or is it built different

[nickpelov]

well this is a problem if you are interesting in power consumption. If you are measruring power capabilities of a power supply then it's not a problem.The ideal situation is to be able to measure the burden voltage and have an option to subtract it or not subtract it depending on what you need. Because there are tolerances in shunts and even worse - the fuse resistance probably has a lot more tolerance than the shunt it would be a good idea to have a calibration procedure for the burden voltage. For example go over the amp ranges and measure burden voltage while passing known fixed current.

[TomKappeln]

1.21GW ... great scott ... Just kidding