121GW VA-Mode Problem & Solution

[@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

[@foxabilo]

Yes, Roger has an uncanny skill of making the complex seem mundane. A real engineer.

[@SIXSTRING63]

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.

[@orionsmith7668]

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

[@station240]

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.

[@movax20h]

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.

[@stuartmp1974]

Really nice. Thanks you for posting such a through video

[@tech29X]

Great video, thanks for your effort.

[@boonedockjourneyman7979]

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

[@KainkaLabs]

It´s homebuild and described here: kzbin.info/www/bejne/aIasZHutjLuki6c Perhaps I will make it a kickstarter project at some time. It´s not so easy to transfer it from a hand-wired product to a PCB-populated product with not too much hand-wiring because the 24-position rotary switches have 2 separate planes and I don´t know if the rotary-switches are available in larger volume. Got mine from a Chineses Ebay seller many years ago.

[@joegennaro8265]

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

[@KainkaLabs]

AFAIK the BM235 doesn´t have a VA-mode. Nevertheless the concept how to connect the load correctly to avoid burden-voltage error can of course also be applied by measuring VA with 2 separate multimeters.

[@joegennaro8265]

@@KainkaLabs thank you for explaining that goodnight

[@foxabilo]

Kainka Cad :-) does dave know yet?

[@KainkaLabs]

Don´t know. Joe Smith has put post about the VA-mode problem in the EEVBlog-Forum section about the 121GW. But the forum-entry has more than 50 pages and I don´t have the time to read all the entries.

[@joesmith-je3tq]

Its been almost two years since I made the original video showing the problem and how to work around it. I assume Dave had watched it because he commented on it. Based on the comments I received, I don't think many people understood what was being shown, including Dave. Rodger's video is clean and easy to follow IMO. Rodger, thanks for taking the time to repeat the tests and for putting this video together.

[@foxabilo]

@@joesmith-je3tq it's a beautiful solution joe, and it does need to be in the manual (pdf /site) I have mailed him to come watch this, hope he gives you a shout out.

[@tech29X]

@@joesmith-je3tq It's a shame when you post the solution on the forum and most don't understand. You're punching higher than most in this league.

[@joesmith-je3tq]

@@tech29X It's all that drain cleaning experience... lol.

[@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.

[@38911bytefree]

It was fixed in a trivial way that does not accept any alternative, plus the range switch resistance is an unknown variable in this product. You need to run a self calibration each time you move it.

[@TomKappeln]

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