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I find this a common fault with single chip DMM's. Firmware writers, youtube testers- all miss it. It's why I have 35 year old clunker DMM's in my collection because they have no firmware and never lie to me
I use this test jig/circuit to flush out the men from the boys. You will be surprised at the results.
Inject say 250mVAC 1kHz sine into a DMM on ACV. Add variable DC offset of either polarity and see what "true RMS" numbers you get. Either the readings are nonsense, or the autoranging screws up, or both. (frequency measurement doesn't work, as expected without zero-crossings).
My theory, when you have significant DC component on an AC waveform, it seems to be when the A/D converter pegs or clips for that range, which gives erroneous readings. Because you're looking at the true-RMS DSP value, it will not show a (DC) saturated A/D with the HPF. The autoranging algo doesn't see a need to range up and thus gets stuck. I would look at the A/D raw number too- but this halves the sample rate.
MESTEK DM-100C, ANENG AN8008 is a bit weird. Boot up, no DC offset, ACV 250mVAC 1kHz reads fine.
AN8008 - switch on with anything over +/-3VDC offset, ACV goes berserk hunting for a range and reading odd numbers. Switch on ACV with no DC offset, then slowly ramp up to 20VDC and it reads fine throughout.
DM100C - add anything over +15/-17VDC offset, goes berserk hunting for a range and reading odd numbers or 0.000 if saturated.
Once a meter sees the big offset, I did see it "remember that" - if I disconnect the signal so the DMM autoranges down, then reconnect the AC+DC signal, I saw it behave differently from then on, compared to a cold boot. Sigh.
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Youtube testers may miss it, but I don't: https://lygte-info.dk/info/DMMReviews.html
I call it "True-AC" in my reviews (Yes, it is a silly name, but I had to use something that was short).
My tests are usually done around a couple of hundred volts where I use AC on DC range and DC on AC range and a combination of AC and DC with AC>DC and DC>AC.
As you conclude many meters fails on this. -
The polarity switch on that schematic looks messed up.
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The polarity switch on that schematic looks messed up.
Fixed, I was half awake.Youtube testers may miss it, but I don't: https://lygte-info.dk/info/DMMReviews.html
I call it "True-AC" in my reviews (Yes, it is a silly name, but I had to use something that was short).
My tests are usually done around a couple of hundred volts where I use AC on DC range and DC on AC range and a combination of AC and DC with AC>DC and DC>AC.
As you conclude many meters fails on this.
Still a bit confusing because there are two measurements - I have a bench DMM withAD637AD536A that has True RMS AC+DC, or AC-only selectable. AC-coupled I would call the measurement "true-AC".
Here it's just bad software engineering, the edge cases are not tested. As I see it, A/D clipping happens and the DMM's firmware bungles the range choice under certain, select conditions. -
curren measurment issue - https://youtu.be/csANYnvL32k
voltage issue - please check Joe YT chanel
I am not tracing this since Joe review, maybe problems are fixed now? I wonder if this new is also having the same problems?
First time I have seen that video.
Just tried to replicate it with the same AC currents and couldn't. Although I was using a low voltage source instead of mains. So
That's a very strange setup. His explanations are practically incomprehensible,so I assume it's a sort of dimmer module and a LED bulb containing an SMPU in series, probably creating a very irregular ac-current waveform with a high crest factor / high DC superposition.
The hardware / software of the GW121 has definitely big weaknesses with superimposed DC on AC signals, which seems to be the case here, again.
Frank
I wonder if this particular case has something to do with the max4238 amplifier. Looking at the disassembled firmware and the 121gw schematics - the only thing different between 5.0000mA and 50.000mA range - seems to be 5.0000mA is being passed through the 4238. So:
5.0000 mA = max4238_x10 -> hy3131_OP1_x10 -> (RMS)
50.000 mA = hy3131_OP1_x10 -> (RMS)
And max4238 seem to have lower BW than the OP:s in hy3131. GBWP = 1.0 MHz vs '2.0 MHz'.
But of course without knowing more of this particular current waveform it’s all just guesswork what’s really happening.
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Youtube testers may miss it, but I don't: https://lygte-info.dk/info/DMMReviews.html
I call it "True-AC" in my reviews (Yes, it is a silly name, but I had to use something that was short).
My tests are usually done around a couple of hundred volts where I use AC on DC range and DC on AC range and a combination of AC and DC with AC>DC and DC>AC.
As you conclude many meters fails on this.
High voltage DC offset values are known to cause issues, particularly so with some meters that have combined AC/DC range switch positions. -
Damn could it be the 150$ meter
Nope.
NOPE???
That meter has a lot of features I could use. So is the EEVBlog about to issue a new range of tools? this gets more and more interesting especially with the blurred out text.. -
This looks like Dave did it intentionaly, otherwise model name wold not be masked.
Nope. I actually had no knowledge of or input to this design at all. It "just appeared" and will be sold under their brand. They made this branded special for me to evaluate to see if I was interested. The 121GW is not being discontinued, unless I decide to do so of course.
It is a physically bigger design, higher CAT rating, better specs, true energy measurement chip, and doesn't appear to be backward compatible with my BT app.
Some of us would find those features very interesting!!!!! -
I had hoped Scott would have chimed in. No doubt that the 121 would have problems, but I could push it enough to make my two normal meters disagree by a fair margin. Guessing it's something like this but would have liked to have seen the waveforms. Oh well.
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NOPE?Damn could it be the 150$ meter
Nope.??
That meter has a lot of features I could use.
I'm sure it does. But the 121GW doesn't even sell for close to US$150 and you expect an even higher end version (true energy measurement, triple display, higher CAT rating etc) to sell for $150?
Again, this meter has absolutely nothing to with the $150 class meter I have been talking about for the last 9 months, that is a different meter. I have placed an order for those and will have them soon enough for those interested in a $150 price class meter. Sign up for my newsletter and you might even get it cheaper than that upon release. -
It took me a second to find this thread, no one put the thread link in the video comments. I was looking under the other 121GW threads. I wasn’t expecting this to be under a “New eevblog multimeter” thread.
I tried to send you a DM to find the thread, but I got a message that the DM was blocked.
That shelly module as I called it in the video (“Shelly1PM”) that I was trying to read the current from has since been installed in the walls. I have another one arriving but shipping has been delayed these days so I don’t know when I will get it. I might have a normal Shelly1 but I will have to look for it.
As for the current measurement on the scope, I don’t own a differential probe. The best I have is a Hantek CC-65, the specs on it are not the best.
Yes, this is the original 121GW from the kickstarter. One was a replacement from Dave after the switch shunt fix for the switch didn’t work on the original one. The other one is the original one that I later fixed after seeing Daves video on a BM235 with the case tolerance causing a switch issue. So I dug it out and tweeted the case to get it working again. It original one also had an issue with resistance readings, but everything else seems to work within spec.I had hoped Scott would have chimed in. No doubt that the 121 would have problems, but I could push it enough to make my two normal meters disagree by a fair margin. Guessing it's something like this but would have liked to have seen the waveforms. Oh well.
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This is a Shelly1PM module, or Shelly as I called it in the video. It’s a remote relay trigger with WiFi for turning on/off switches in the wall. It doesn’t do any dimming. It’s a smart home IOT device.
The crest factor according to my Fluke 298 is about 5.0 if I recall correctly. I think you asked this in a comment on the video.
The 121GW did this when trying to read the current of a Shelly1PM, its a relay smart module that also measures the current being used back to the app. This was found when trying to see the difference in current being used between a Shelly1 standard module and a Shelly1PM.
It wasn’t anything to do with the LED nightlight I grabbed from the kids bathroom. The LED light was just to demonstrate that once the load went over a certain range the 121GW would flip over from the 5mA range to the 50mA range.
The Shelly1PM I had wired would use about 12mA to 13mA without the relay activated and the 121GW showed 4.88mA, not yet at the top of the 5mA range.
When I turned on the relay it would use about 17mA to 18mA, you will see the 121GW max out at the top of the 5.2mA range, but still wont flip into the next range.
When I added the additional load of the LED bulb for another 2.5mA this was enough to force the 121GW to change ranges and display it correctly.
Originally I had a regular LED light plugged in that uses about 10mA, but was curious to see if a smaller load would also be enough to flip the range on the 121GW.curren measurment issue - https://youtu.be/csANYnvL32k
voltage issue - please check Joe YT chanel
I am not tracing this since Joe review, maybe problems are fixed now? I wonder if this new is also having the same problems?
That's a very strange setup. His explanations are practically incomprehensible,so I assume it's a sort of dimmer module and a LED bulb containing an SMPU in series, probably creating a very irregular ac-current waveform with a high crest factor / high DC superposition.
The hardware / software of the GW121 has definitely big weaknesses with superimposed DC on AC signals, which seems to be the case here, again.
Therefore, in such situations, an overrange condition is not detected properly, and then a clipping occurs in too a low range, exactly what this guy demonstrates when he uses a fixed, upper range.
So that's nothing new, and has been discussed in length already. (superimposed DC on AC in ACV mode, w/o giving a high voltage warning)
Frank -
but I could push it enough to make my two normal meters disagree by a fair margin.
And what was the correct value? Was the Brymen or the Fluke closest or where they all quite a bit off? -
This is a Shelly1PM module, or Shelly as I called it in the video. It’s a remote relay trigger with WiFi for turning on/off switches in the wall. It doesn’t do any dimming. It’s a smart home IOT device.
Power factor according to my Fluke 298 is about 5.0 if I recall correctly. I think you asked this in a comment on the video.
The 121GW did this when trying to read the current of a Shelly1PM, its a relay smart module that also measures the current being used back to the app. This was found when trying to see the difference in current being used between a Shelly1 standard module and a Shelly1PM.
It wasn’t anything to do with the LED nightlight I grabbed from the kids bathroom. The LED light was just to demonstrate that once the load went over a certain range the 121GW would flip over from the 5mA range to the 50mA range.
The Shelly1PM I had wired would use about 12mA to 13mA without the relay activated and the 121GW showed 4.88mA, not yet at the top of the 5mA range.
When I turned on the relay it would use about 17mA to 18mA, you will see the 121GW max out at the top of the 5.2mA range, but still wont flip into the next range.
When I added the additional load of the LED bulb for another 2.5mA this was enough to force the 121GW to change ranges and display it correctly.
The 5mA range does not 'max out' at 5.2mA - it will actually read up to 5.4999mA before it needs to change range.
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So it’s not really a question of 121gw ‘getting stuck’ (as mentioned in the video) and wont auto-range. But instead it’s reading the waveform ‘wrong’ and showing too low value in the lowest 5.0000mA range. But in the next range 50.000mA it’s reading it correct.
According to the manual ACA measurements is specified for 45 to 1000 Hz.
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If a shitty Aneng meter is showing correctly it's not a bandwidth issue ... maybe the 10x op-amp is not up to the task and is latching or something
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I did find another Shelly1PM and a standard Shelly1, I thought I saw them when we rearranged the office the other day.
Attached is the capture from the scope from the PM version since that’s the one I used in the video. Keep in mind that I am using a Hantek CC-65 that is rated for the lowest reading of 20mA although I have seen this go down to 5mA before it fails.
I tested this with looping the wire on the clamp two and three times and had the same waveform without the loop.
I also confirmed this Shelly1PM exhibited the same behavior using the 121GW, as did the standard Shelly1.
I am also including two screen shots.
The one with 11.5mA is just the shelly being powered.
The one showing 20mA (actual is 18.5mA) is just the shelly engaging the relay without any light bulb.
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Youtube testers may miss it, but I don't: https://lygte-info.dk/info/DMMReviews.html
I call it "True-AC" in my reviews (Yes, it is a silly name, but I had to use something that was short).
Unless I am overlooking something, I don't see a "True AC" column on that page. Maybe you could add it - it would be useful, rather than having to go through the reviews one-by-one. -
I did find another Shelly1PM and a standard Shelly1, I thought I saw them when we rearranged the office the other day.
Attached is the capture from the scope from the PM version since that’s the one I used in the video. Keep in mind that I am using a Hantek CC-65 that is rated for the lowest reading of 20mA although I have seen this go down to 5mA before it fails.
I tested this with looping the wire on the clamp two and three times and had the same waveform without the loop.
I also confirmed this Shelly1PM exhibited the same behavior using the 121GW, as did the standard Shelly1.
I am also including two screen shots.
The one with 11.5mA is just the shelly being powered.
The one showing 20mA (actual is 18.5mA) is just the shelly engaging the relay without any light bulb.
Thanks for the current traces. It seems fairly simple to reproduce the problem with 60Hz square wave and 12% dutycycle (roughly simulating that current waveform). If DC offset is then increased or lowered - in 5mA range something seems to go into saturation and the wrong value is shown.
It really seems like it is the max4238 causing it. But not the OP it self but the fact that the signal gets amplified 10x. Further investigation is needed why something further down the line doesn't seem to like this.
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It took me a second to find this thread, no one put the thread link in the video comments. I was looking under the other 121GW threads. I wasn’t expecting this to be under a “New eevblog multimeter” thread.
I tried to send you a DM to find the thread, but I got a message that the DM was blocked.
If you log onto your Youtube account, then select customize channel, video manager, comments then select "held for review" or "likely spam". My guess is you have a few in there by now. Links will typically be picked up by one of the filters.
I was using a pulse to create the picture I uploaded, very similar to what you show. This doesn't surprise me that the 121 has a problem with it. As you can see, in my particular case even my other meters differ. -
If you log onto your Youtube account, then select customize channel, video manager, comments then select "held for review" or "likely spam". My guess is you have a few in there by now. Links will typically be picked up by one of the filters.
I was using a pulse to create the picture I uploaded, very similar to what you show. This doesn't surprise me that the 121 has a problem with it. As you can see, in my particular case even my other meters differ.
I check the comments every few days since I block an extensive list of words from my security days that I created a while back, and yes yours got blocked by the URL. Youtube Studio usually shows a number next to the published, held for review, or likely spam comments but not this time. This time I had to go into held for review to see the new comments held. They keep changing studio, errr.
Thanks for the URL, at least I did find it. I guess you didn’t need the CSV file, it looks like you already replicated it.
Scott
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If you log onto your Youtube account, then select customize channel, video manager, comments then select "held for review" or "likely spam". My guess is you have a few in there by now. Links will typically be picked up by one of the filters.
I was using a pulse to create the picture I uploaded, very similar to what you show. This doesn't surprise me that the 121 has a problem with it. As you can see, in my particular case even my other meters differ.
I check the comments every few days since I block an extensive list of words from my security days that I created a while back, and yes yours got blocked by the URL. Youtube Studio usually shows a number next to the published, held for review, or likely spam comments but not this time. This time I had to go into held for review to see the new comments held. They keep changing studio, errr.
Thanks for the URL, at least I did find it. I guess you didn’t need the CSV file, it looks like you already replicated it.
Scott
Yeah, don't get me started on YT. My only saving grace is that I don't use it often.
I tried running 100 or so different symmetrical waveforms to compare the 121 against the Fluke 189 and didn't run into any problems so I assumed it was some sort of large one sided spike. I had put this program together (attached) many years ago to drive my arb. It really needs to rewritten but instead, it gets mod after mods and's a real mess. The last thing I did was port it to Windows 10, so no more Win XP VirtualBox. Some things work, others don't.
But it's really flexible.
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I did find another Shelly1PM and a standard Shelly1, I thought I saw them when we rearranged the office the other day.
Attached is the capture from the scope from the PM version since that’s the one I used in the video. Keep in mind that I am using a Hantek CC-65 that is rated for the lowest reading of 20mA although I have seen this go down to 5mA before it fails.
I tested this with looping the wire on the clamp two and three times and had the same waveform without the loop.
I also confirmed this Shelly1PM exhibited the same behavior using the 121GW, as did the standard Shelly1.
I am also including two screen shots.
The one with 11.5mA is just the shelly being powered.
The one showing 20mA (actual is 18.5mA) is just the shelly engaging the relay without any light bulb.
Hello Scott,
many thanks for your oscillograms! Very interesting.
So inside these modules are small and simple SMPUs, which create small square wave current pulses, which have a high Crest factor, like the problem in ACV, with high DC superimposed.
The 121GW, like many other DMMs, calculates the RMS by fast digitizing and directly calculating the sum of the squared values of the samples.
The amplitude of about 55mApp of these pulses in the idle case would normally create an overrange, as this is 10 times the 5mA range, which is for some reason not detected by the HY3131, or by the SW.
Dave has built in an additional x10 amplifier to feature 'low burden' on the current ranges, and the HY3131 provides additionally two selectable x10 stages. So I assume, that an undetected analogue signal clipping inside the HY3131 occurs. 55mAp over 1 Ohm shunt give 55mVp, times 10 once gives 550mVp, and then calculated in the 50mA range to give about 12mArms. That's clipped to a display of about 5mA in the 5mA range, i.e. factor 2.5 low, i.e. one of the amplifiers, or the A/D is clipping at about 2.2Vp.
This makes sense, as the HY3131 is powered from3.3V3.6V, and AGND is at about 1.2V, so the positive margin is 2.4V.
So as the fast A/D should be able to handle high Crest factiors, i.e. high peak amplitudes, there should be a window comparator (in SW?) to detect any pulses at its input higher than2V+/-1V, or so, to range up in that case, although the RMS value does not exceed the current range yet. .. I've tried to figure out from the datasheet, from the configuration manual, and from the circuit diagram, how to detect such an overload condition, but could not find out, how to do this properly.
Frank -
Am I the only one that can't get excited about a new EEVblog-branded multimeter in light of the 121GW issues? I don't understand why it seems uncared for.
If the ACV autoranging bug is severe - failure to display hazardous live invalidates 61010 approval, this is a safety function. If it were me, I would be lighting a fire under the programmer's ass to get this bug fixed asap. A manufacturer having awareness of a safety problem and not acting or warning on it, lawyers advise it's a very bad situation. I don't know what the problem is, but UEi might be interested.
I could be wrong or overreacting here, but I have expectations of a brand and this is no fun.
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Same here and i find the related threads slowly drifting away ... i dont need to see testo meter brand or fluke t6 clamp meter
I'm in need of at least 2-3 new meters at my job, and i need an autohold badly ... i make tons of measurements and the old flukes we have are getting tiresome to use ...
I had very high expectations for the 121gw ... maybe too high ?