Let's not confuse "electrical robustness" with safety. I have yet to see a failure mode on these meters that will hurt the user.
Giving misleading readings is the only safety issue I've seen so far - how difficult would it be to design a meter with a universal HV warning? (AC, AC, DC+AC) Some indicator telling the user if it's safe or not even if the meter can't correctly display the reading.
Maybe it has already been discussed before in this thread, but I am wondering why there are no cheap Fluke clones with good electrical robustness. Most of the techniques are in plain sight. Just copy the board with big clearances, large fuses and MOVs. It may cost a few more dollars for parts, but the margin for "professional" multimeters is much larger.
Because:
a) There's no need, sales of unsafe meters are doing just fine.
b) Certification costs money and you're not going to sell many meters without certification marks.
c) Once a meter is certified you're not allowed to change a single component supplier or any part of your production line without going through re-certification.
I suspect (c) is a real problem for Chinese meter makers.Fungus, "c" is only valid if you apply for their "listed" program (UL, TÜV, Intertek, etc.). The listing requires annual inspection to the manufacturing plant audits and process reviews. Most Chinese low cost meters do not go through that, but that does not solely explain lack of safety: several japanese brands (Samwa, Hioki) have excellent quality and reputation and also do not have markings.
I have been involved with projects where "c" was required but wouldn't think this was required for a DMM. For example, say your JEDEC 4007 from company X is no longer offered, I doubt you would be required to stop production until you get your new diode certified. Have anything to back up this statement?
Maybe it has already been discussed before in this thread, but I am wondering why there are no cheap Fluke clones with good electrical robustness. Most of the techniques are in plain sight. Just copy the board with big clearances, large fuses and MOVs. It may cost a few more dollars for parts, but the margin for "professional" multimeters is much larger.
Because:
a) There's no need, sales of unsafe meters are doing just fine.
b) Certification costs money and you're not going to sell many meters without certification marks.
c) Once a meter is certified you're not allowed to change a single component supplier or any part of your production line without going through re-certification.
I suspect (c) is a real problem for Chinese meter makers.Fungus, "c" is only valid if you apply for their "listed" program (UL, TÜV, Intertek, etc.). The listing requires annual inspection to the manufacturing plant audits and process reviews. Most Chinese low cost meters do not go through that, but that does not solely explain lack of safety: several japanese brands (Samwa, Hioki) have excellent quality and reputation and also do not have markings.
I have been involved with projects where "c" was required but wouldn't think this was required for a DMM. For example, say your JEDEC 4007 from company X is no longer offered, I doubt you would be required to stop production until you get your new diode certified. Have anything to back up this statement?I don't have anything to back your statement about "production stop due to the lack of certification". This is an exception that would probably be negotiated between the cert agency and the manufacturer.
My experience with the marking process and audits is related to a few products (not DMMs) we were releasing in the past few years. We didn't fall for the siren songs from the cert agency (ies) as the markings didn't add value to our products, therefore I don't know how the exception would be dealt.
Happy new year, BTW!
I'm a little lost. Fungus made the statement in regards to meters which I don't believe they would be held to C. Are you asking under what circumstances we were or just merely pointing out that I did not provide any details?
It seems I saw it on 60 minutes. Doing a search, I came up with the attached from "Proposed Legislation Regarding Whistleblower Protection: H.R. 2579 ..., Volume 4":
I'm a little lost. Fungus made the statement in regards to meters which I don't believe they would be held to C. Are you asking under what circumstances we were or just merely pointing out that I did not provide any details?I guess the lines were crossed somehow. I was a bit confused and understood that you were asking me to provide documental proof about an assertive I haven't made. Nevermind. It is still early in the year...
Quite interesting story. The snippet of document you sent has a striking resemblance with the whole 737MAX brouhaha: "Today consultants and private contractors not only build projects, they regulate them."
I was amazed how fast the 121 seem to react to temperature changes. So here I have taken the green mV trace, flipped it vertically and overlayed on the two temperature traces where red being 121 internal temp and white the chamber temp.
....
Edit: correction! those two screenshots I've merged perhaps wasn't from the same sweep and therefor not in sync to begin with.
Left scale is voltage, right temperature. White is chamber temp, Red 121's ambient, Green reported voltage. Samples are roughly at 2Hz and lag is about 170 seconds. Of course, the time to settle is actually well over an hour in this case..
The latest spreadsheet is now available on GoogleDocs here:
https://docs.google.com/spreadsheets/d/1cXzYpIoyVm9QJUju4KXqM22CEQZP3_xwWvDyeVwxTy4/edit?usp=sharing
The latest spreadsheet is now available on GoogleDocs here:
https://docs.google.com/spreadsheets/d/1cXzYpIoyVm9QJUju4KXqM22CEQZP3_xwWvDyeVwxTy4/edit?usp=sharing
This spreadsheet seems out of date?
A bit late, but I can say, every Meterman PM55 or Amprobe PM55A I have has failed.
What happens:
- Auto mode freaks out and doesn't work (a short shows an unstable high resistance for example)
- Short detect mode shows shorted
- EF (power stick) mode works
- I can't remember what Low-Z volts does
- Hi-Z voltage works
- Diode mode acts like a short
- High ohms varies from not working to usually sounding the "shorted" beeper; IIRC high ohms will not give a stable reading
- Haven't tested current
What causes this?
The only similar thing I could find was a dying battery.
I purchased a new unit after my PM55A had failed, only to find a PM55 I gave to a friend also failed. I tested a PM55 I had and it too had failed. The replacement? Well, it tested good (testing 5V in auto mode, and shorting probes, that's it...); after a month when I went to use it to test a low voltage DC circuit again, it showed low battery ... and sure enough it failed too.
I'd like to fix them but have no idea where to start or what could have failed.
I'm later still to the game, but I also had problems with the PM55A (and I have mentioned the problems with PM55A on the forum). I own two of them, one bought, one found in a trashcan (no, really!). They are utterly unreliable with constant "restarts" and who can have confidence in a meter that actually have an "reset" procedure printed on the back?
But I may have a "fix". Instead of one CR2032, try two CR2016. It seems almost like the design had two batteries in mind. Of course, this "fix" more than halves the battery life and doubles the battery replacement cost, and 6 volts may still be too much for the design. With two 3 volts button cells, the constant restarts, confusion in auto mode and such disappeared and the meters seems stable. But still, I seldom use them anymore, since I don't really have confidence in them anyway.
Dave was posting hints about some new meter he was planning to sell but that seems to have cooled down.
Dave was posting hints about some new meter he was planning to sell but that seems to have cooled down.
The usual delays.
Just got an email that it will be going into UL testing very shortly and they want me to report any issue now (was supposed to have been through UL before, I guess it didn't, or they changed it for whatever reason).
Dave was posting hints about some new meter he was planning to sell but that seems to have cooled down.
The usual delays.
Just got an email that it will be going into UL testing very shortly and they want me to report any issue now (was supposed to have been through UL before, I guess it didn't, or they changed it for whatever reason).Are you brave enough to send one to Joe ?
Ok looking forward to that. Didn't know UniT had some new meters.
The efford&time you make to test these meters to the extreme is impressive.
And sometimes funny, when you killed that UT181A with just 1 click of the grill starter You so much wanted to like that meter, your reaction was priceless
In my experience it's pretty quiet in multimeterland especially on top models from the better brands. I suspect that most large brands are working on really intergrating logging/data processing, communications and maybe touchscreen etc (for instance, the fluke 289 has been 12 years on the market or so?, brymen doesnt have a real top model logging meter etc etc).
Dave's 121gw is I think one of the latest 'higher end' meters. And I think gossen replaced the series that you tested (the 300k count one), but with a similar capable model. Maybe/hopefully one without the multiple faults you've discovered
Kiss Analog already did an interesting review on this meter (well, the previous 90DM600 model but its probably the same):
It appears the 90DM600(DT-9560) costs $86.18 and the 90DM610 (DT-9561) is $49.00.
I have not checked CEM to see what the differences were. I would not expect them to behave the same when tested.
No I don't really have the need for another 6k count meter as I already have several.
Also I live in europe, so there is at least a ~$30 charge for transport and taxes for the amazon meter, so it would come very close to the price of a bm235 (BM235 is here about ~€85).
Then the price difference becomes pretty low and the bm235 is of course a meter that has proven itself so for europeans that might be the better deal (or one of the higher brymens, they are priced pretty well here).
I think this meter is mainly a potential good deal for US based buyers on a tight budget, maybe young hobbyists that are starting with their electronics hobby (I can't see US shipping costs, but I presume it can come delivered free of charge with amazon prime or so).
I was mainly amaized at the US retail price for a UL listed/iec61010 compliant DMM (apart from whether these specs add something to the meter or not).
Normally for that price you sometimes don't even get ceramic sand filled fuses.