| Products > Test Equipment |
| 121GW RF Issue |
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| joeqsmith:
--- Quote from: wolfy007 on September 04, 2023, 03:11:51 am ---I watched Joe's videos, and I did a quick test and found I had a similar problem with my GW121, Ill put my replies to his video here also; ... "PS: couldnt help it, also tried an Agilent U1253A (MY51400064), Fluke 189 (75240037), 289 (35740002), 8060a (7720020), Uni-T UT181a (C171835804), Tektronix DMM916 (144966) and even an Owon B41T+ (21340133), thankfully no other noise issues (even tried with a MHz noise generator transmitting in the background)." --- End quote --- Thanks for trying to replicate what I saw with the 121GW. The only others I have that may be worth looking at are my TPI (Summit) 194II, Yokagowa TY720 and maybe the CEM DT-9938. I would need to check their specs. Still, this a poor way to test meters as it's not controlled. I expect IEC 61326 requires the meters pass the industrial electromagnetic environment at 10V/m, performance criterion A. This means no degradation of performance during the test. .... OK, I think I see the problem. Looking at the backside of my 121GW, they are not tested to 61326. Even if they were, then do I trust the people testing the products..... |
| EEVblog:
Confirmed. The reading peaks (about 0.25mV) at 110MHz (500mV level). Above and below 110MHz-ish it's basically zero. I was also able to reproduce this on the Keysight U1282A, but that peaks at 66MHz and gives a higher reading than the 121GW for the same RF signal level. The Keysight also gives a reading about half at 36MHz. Nothing on the 121GW at 36MHz. For reference, both meters use the HY3131 chipset. I will branch out this to a new thread, it does not belong here. UPDATE: The Fluke 17B also does this at about 120MHz, at 0.4mV reading. Doesn't look as bad though of course it's only 100uV resolution, not 1uV resolution, but the reading is actually higher than the 121GW. The BM235 also does this, up to 0.4mV depending upon the location of the leads physically. The Keysight U1272A also does this (0.4mV) at 36MHz. I have a recollection this is nothing new and has been discussed a few years back? |
| joeqsmith:
--- Quote from: EEVblog on September 04, 2023, 05:14:52 am ---I have a recollection this is nothing new and has been discussed a few years back? --- End quote --- It's very possible. My goal was to provide some idea how accurate my 7 YO Brymen is in the DC modes after it was suggested they need yearly alignment. To gain some confidence in my measurements, I wanted to run a different brand meter. I don't own a lot of high res handhelds and the first meter I grabbed was the 121GW. I wasn't thinking RF and never thought I would run into problems making such a simple measurement. I tossed it aside and grabbed the GMW for a comparison. I suspect every meter is susceptible to RF. One time during my career I had to use an outside lab for testing and when I arrived, there was a tomahawk cruise missile in the lobby. They had capability for testing several GHz at 1000V/m. At that time most of my involvement was at 100V/m. I've damaged electronics at that level. For the last few decades anything I have been involved with is only tested to 10V/m. As I mentioned during the video, even at these low levels, I have seen handheld meters (even Fluke products) that were effected. 61326 radiated immunity starts at 80MHz. Below this is conducted. |
| EEVblog:
--- Quote from: joeqsmith on September 04, 2023, 02:49:58 pm ---As I mentioned during the video, even at these low levels, I have seen handheld meters (even Fluke products) that were effected. --- End quote --- Fluke famously had to redesign the 87V after my video showing that a GSM mobile phone nearby could brick it. Took them a year to get the new model rolled into production. |
| EEVblog:
--- Quote from: joeqsmith on September 04, 2023, 04:27:15 am ---Still, this a poor way to test meters as it's not controlled. I expect IEC 61326 requires the meters pass the industrial electromagnetic environment at 10V/m, performance criterion A. This means no degradation of performance during the test. .... OK, I think I see the problem. --- End quote --- The only meter I know of that's specifically EMI marketed 61326-1 is the "double shielded" Brymen BM2807CSE. That's it's big marketing claim, for high EMI enivironments. But even that is only specified for 3V/m, and even 1V/m for some functions (all +100 digits) The BM869 is only tested to 3V/m under 61326, but it's +1000 digits. And AFIK it doesn't mean "no degredation", which is why Brymen for example specify nominal accuracy +1000 digits for 3V/m |
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