Handheld meter robustness testing

[joeqsmith]

That was some box that I had shown up.  Name was pretty close.   

That analog meter is still sitting in the box and I had planned to run it next.   I think I am going to side step that and run this CEM meter. I had wanted to run the Extech EX540 but it was in such poor condition and needed some repairs.  So next up, the CEM DT-9939.   If there is anything you would like to see while it is still functional, just ask.   

http://www.ruby-electronics.com/store_item/DT-9939_Waterproof_Industrial_Wireless_USB_RMS_Multimeter_with_Capacitance_Frequency_Duty_Cycle

[joeqsmith]

I have completed my review of the CEM DT-9939 I bought from Ruby Electronics for $120.  40,000 count, AC+DC, wireless, tri-display, GS and TUV certified.     

[Muttley Snickers]

G'day Joe,

Thanks for the video it was very good and I think you did pretty well on price for the CEM, Jaycar down here did have them for $229 AUD not long ago but recently put them up to $279 AUD, I've owned a few CEM meters over the years and recently gave one away to my brother in law whom I don't like very much, one thing to watch out for is they have a tendency to go out of specification with even the slightest bounce on the bench because of the trimmers, easy fixed but still a pain.

Jaycar do offer a life time guarantee on the CEM meters which I have tested and they did come to the party on one I blew up, one thing to watch out for though is their current catalogue states a life time guarantee but the website states only 9999 months which equates to only 833.25 years, this could be a bit of a worry for immortals.

Jaycar - Digitech QM-1576
https://www.jaycar.com.au/ip67-true-rms-cat-iv-dmm-with-meterbox-smartphone-app/p/QM1576

[3nigm4]

...one thing to watch out for is they have a tendency to go out of specification with even the slightest bounce on the bench because of the trimmers, easy fixed but still a pain.

I think that adding a voltage reference (like done un the UT61E) may improve this... I'll take a look... if I find it's schema

Jaycar do offer a life time guarantee on the CEM meters which I have tested and they did come to the party on one I blew up, one thing to watch out for though is their current catalogue states a life time guarantee but the website states only 9999 months which equates to only 833.25 years, this could be a bit of a worry for immortals.

Jaycar - Digitech QM-1576
https://www.jaycar.com.au/ip67-true-rms-cat-iv-dmm-with-meterbox-smartphone-app/p/QM1576

I investigated a bit, disassembling Meterbox apps to look for names used in BT connetion; I planned to replace the internal RF module with a BT module, but trying an HM-10 (BLE), it is seen by apps only if named DM-9969 or DM-9989 that are those sold with a BLE module.
In the code I've found DT-9939 but even a strange DT-9939B... looking to QM-1576 seems that it is the only DT-9939B on the market: a DT-9939 with a BT module while the one with RF module is the QM-1575

Edit: the QM1575 cost even less
https://www.jaycar.com.au/40-000-count-ip67-true-rms-cat-iv-dmm-with-wireless-usb-and-storage/p/QM1575
Edit2: it seems no more listed as an available choice (thanks to Muttley Snickers report)

[Muttley Snickers]

Greetings 3nigm4,

I think you might find that the Jaycar listing for the QM-1575 you posted could in fact be a stale Google page as Jaycar no longer list that model in either their current paperback catalogue nor on their site when you search for that model number or check the list of digital multimeters. If they were still available at that price then I would buy one tomorrow without hesitation.

 

[3nigm4]

It seems they forget to remove the page too 

[joseph nicholas]

Hi, The reviews and testing are excellent on joe's posts.  Of all the meteres he shows in the rap up, the cheap Uniti e model looks to be the best bang for the buck.  The tri state display on the Jaycar meter featured there and the water proof thing are nice but I guess I admit I don't get it.  All these expensive meters would most likely would not be used in the field.  In a work setting, I think something like a MF-47 analogue Simpson clone would make me more comfortable since it can measure up to 2.5K without blowing up.  Most of these high end meters are going to see service in the on the bench, not during a rain storm hanging from a high tension pole. 

[joeqsmith]

...one thing to watch out for is they have a tendency to go out of specification with even the slightest bounce on the bench because of the trimmers, easy fixed but still a pain.

I think that adding a voltage reference (like done un the UT61E) may improve this... I'll take a look... if I find it's schema

If you find a schematic for it, please post it.  I have used the Extech for several years now.  Beyond loaning it out where one person felt the need to turn the selector past the dead stop along with getting it back with a blown fuse now and then, no problems.

That selector switch could stand a redesign, along with the PCB and front end..... 

Hi, The reviews and testing are excellent on joe's posts.  Of all the meteres he shows in the rap up, the cheap Uniti e model looks to be the best bang for the buck.  The tri state display on the Jaycar meter featured there and the water proof thing are nice but I guess I admit I don't get it.  All these expensive meters would most likely would not be used in the field.  In a work setting, I think something like a MF-47 analogue Simpson clone would make me more comfortable since it can measure up to 2.5K without blowing up.  Most of these high end meters are going to see service in the on the bench, not during a rain storm hanging from a high tension pole. 

Thanks, glad you enjoy them.  I guess when it comes to what products we buy, what we call high end, the bang for the buck and what we are comfortable is a matter of choice.  For work, it may be mandatory.

One day, I may run something I would consider higher end.   The 87V which is the highest cost meter I have ever looked at did very poor so I think I would want to try a Gossen with their GDT protection.  It can't be as bad as the Keysight meter I looked at. Someone asked me about running a new HIOKI pocket meter and had I been able to find one, I would run it.

The 61E aside from not being certified, no backlight (in case I crawl under the car), no temperature and the fact that it can be damaged with such little effort, I would have no need for it.  But the HF free meter may be a better bang for the buck.  I know it was not in the line up because I have destroyed every one of them I have looked at.   This 61 is the 3rd one I've looked at and the only reason it is still alive it because it was reengineered by a state side hobbyist.   Same for the UT181A. 

[joeqsmith]

A friend of mine had purchased one of the Ruby CEM meters and received it today.   Theirs was also the blue CEM with the TUV/GS markings.  They gave me their old meter.  Picture attached.  I plan to keep this one because I find it so funny to see the Vicor logo on it.   

Much nicer shunt and a replaceable fuse than what HF gives away now. 

[joeqsmith]

Viewership has grown enough that today I have started working on an FAQ sheet for this testing.  Hoping that will help out down the road.  Just finished reading every YT comment.  Once completed, feel free to add comments about common questions you feel I have not addressed.   

I have noticed people trying to use the channel to run ads now.   I am not sure if reporting them (youtube allows it) really helps.  So far, I just add them to the banned list.  Strange as my account should be so far in the noise floor, seems using a more popular channel would make more sense.   

Time to read 45 pages of this thread.  The down side of testing....

*******************************
Wow, that's a long thread.   I erased a few posts that didn't add any value (mostly where I would update the spreadsheet) and I have a bad habit of having extra blank lines at the end of posts which I cleaned up. 

Two years of meter carnage and we remained civil enough that the thread remained open!      

Lot's of great comments and questions.  Will make a for a good document moving forward.  Not that people will read it but at least I can now just refer to it if someone asks a common question.   

[joeqsmith]

Answers to Frequently Asked Questions may be found in the following link. 

https://docs.google.com/document/d/1gEPFeOZpsNSm0-7sA98w2P5XE5x77Oal9dQEYvQnF6g/edit?usp=sharing

[rsjsouza]

Viewership has grown enough that today I have started working on an FAQ sheet for this testing.  Hoping that will help out down the road.  Just finished reading every YT comment.  Once completed, feel free to add comments about common questions you feel I have not addressed.   

I have noticed people trying to use the channel to run ads now.   I am not sure if reporting them (youtube allows it) really helps.  So far, I just add them to the banned list.  Strange as my account should be so far in the noise floor, seems using a more popular channel would make more sense.   

I guess that is the downside of being mildly popular... Perhaps they think they can get away with the fact the channel owner likes the traffic of the comments to increase its own popularity... I don't know - Youtube ratings and algorithms can be mysterious.

[joeqsmith]

Viewership has grown enough that today I have started working on an FAQ sheet for this testing.  Hoping that will help out down the road.  Just finished reading every YT comment.  Once completed, feel free to add comments about common questions you feel I have not addressed.   

I have noticed people trying to use the channel to run ads now.   I am not sure if reporting them (youtube allows it) really helps.  So far, I just add them to the banned list.  Strange as my account should be so far in the noise floor, seems using a more popular channel would make more sense.   

I guess that is the downside of being mildly popular... Perhaps they think they can get away with the fact the channel owner likes the traffic of the comments to increase its own popularity... I don't know - Youtube ratings and algorithms can be mysterious.

Yea, I don't mind putting in the time to make these tests happen, buying the meters and make it all available for free.  But why would someone feel it's ok to try and make a buck off it, just poor character IMO.   

[gby]

I was in the market for a fairly high feature high resolution meter that could interface with a PC when I read the last few posts and watched Joe's CEM DT-9939 video review.  Being curious I sought out Ebay to see what they were going for there and found a number of active auctions with starting price of $89.95 with $19.95 shipping.  Some listings by Ruby Electronics and some by other seller names....but all shipping from Saratoga, CA with the same prices.  Long story short I got one for $109.90 delivered and just got it yesterday.  I bought from an alternate seller name ab3c but inside the case was a Ruby Electronics orange card.  So far I like it and it seems reasonable for what it is....a middle level meter in accuracy but high level meter in features, resolution.

However, when I first started checking it out it did some weird things that made me think it was defective.  The first time I turned the knob to Hz% with leads open circuit I got 0's and the meter froze.  Turning to another position did nothing.  I had to go to turn the knob to the off position to get it working again.  I then tried Ohms followed by the continuity setting.  In the continuity setting once I shorted the leads the beeper started and continued going even when I un-shorted the leads  !  I turned the knob to another position and the beeping continued.  I had to go back to the off position to un-freeze the meter.  It did this multiple times.

To make a long story short it was the Golden Power 9V battery included with the meter.  Open circuited it measured 8.3 Vdc but loaded with 220 Ohm it dropped right away to 6.9 Vdc.  Removing the load it went back up to 8.3 Vdc.  With this battery in the meter the low battery indication did not come on since at low load it was high enough.  With a load like the continuity test it seemed it went low enough to "crash" the meter chip.

I put in a fresh Duracell 9V battery and everything works as it should.  So, word to any owners out there that old/high droop batteries may not trigger the low battery indication but the meter works badly/"crashes".

The included Golden Power 9V battery was stamped 2014-07 on the bottom and the calibration check sheet was dated 2013-5-14.  So, I highly suspect these are old stock meters that were made at least 2 years ago.

[joeqsmith]

Hope you enjoy the new meter.  A friend bought one as well and when he went to turn it on, the meter was dead.  Same GP battery.  What was strange is the battery reads about 9.4 volts until you plug it into the meter.  Then it's dead.  Almost like it has a bad crimp.   I saved the battery and plan to pull it apart.   

Problems I have seen with them so far:

Antenna placed on wrong side of PCB shorting to shield
Missing shield
Ground spring cut
Switch contacts not making contact with PCB
Cracked plastic sleeve over banana connector
Open solder joint in RF adaptor
Missing star washer
Missing screws in RF adaptor
Shield over control IC not placed correctly or poor soldering in this area

As long as you are willing to double check the meter over and correct any quality problems, its a great meter for the price. 

[joeqsmith]

I am not sure why but my subscribers are starting to increase at a faster rate.  It seems only fitting we should do something special once we hit 2000 so I have opened a poll where you can decided what meter should be ran to celebrate this milestone. 

[joeqsmith]

This was the second analog meter I bought to check.  It was sold under the Tekpower brand as a PN# TP 7050.  It appears the OEM is Ketai Instrument  KTI and their PN# is KT-7050. 

I've picked this thing up at least five times to run it, but I keep putting it back in the box.

The meter is made with mostly surface mounted parts.  Its much nicer than the first one but costs about 3X.  Notice they have a couple of MOVs in there.  There is a note in the lower right corner of the meter plate "fuse & diode protection".

One thing I don't like is they don't have a separate connector for the low current input.  Then they use glass fuses.  If the fuse blows, the meter will no longer function.  So, if I hit this thing with a transient and the fuse blows, I would have to continue to replace it.  So here lies the reason the meter sits.   

I thought about trying to modify their design similar to what I had done with the first analog meter and see if I could improve it but the schematics don't appear to be available.

[joeqsmith]

A few people have commented about using my grill starter for running some simple ESD tests on these meters.  Some think it's pretty harsh compared with the real world.  I am thinking about trying to make my own simulator.  A quick search, I see it's come up before. 

https://www.eevblog.com/forum/projects/diy-esd-gun/


After I damaged the UT181A, I was asked about the open circuit voltage of the starter and decided to add a little section on ESD testing.  You can see that here:

https://youtu.be/1kYcY2ogmqo?t=113

What I would like to do is design one that would follow the EN61326 standard.  My plan is to run direct contact and just use a fixed voltage.  There are some differences between the IEC standards and what we used to call the HBM.  Rise times are much faster.   When I designed the other transient generators, the rise times are actually fairly slow.  I can see this being a challenge for the ESD pulse.   

Another key difference between these standards is the rise time of the voltage strike. The HBM model specifies a rise
time of 25 ns. An IEC pulse has a rise time of less than 1 ns and dissipates most of its energy in the first 30 ns. If it
takes 25 ns to respond, the device rated using the HBM specification can be destroyed before its protection circuits are
even activated (see Figure 1).



I have attached a paper published by ON Semi that explains a little more about the ESD pulse.  The paper also gives some background and what you could expect to find in the wild.   

[joeqsmith]

I have yet to find any pictures of a gun taken apart.  This article mentions the case design. 
http://incompliancemag.com/article/a-brief-history-of-electrostatic-discharge-testing-of-electronic-products-2/

Time to do a little patent research. 
https://www.google.com/patents/US4926285

If I can get something made that is better than the grill starter (seems like 1A 5ns pulse would not be too hard to improve), my plan would be to test the meters with the leads supplied with them.   I am not really sure how they test them for the EMC cert.   Rerun  the meters I have and then maybe get a couple of UNI-T or anther Vici that failed and rerun them as well. 

[joeqsmith]

The more I read, the more I wonder if it could be done at the home hobbyist level.  I think I just need to try a few ideas and see how things look.  The standard calls for 4KV.   Went through the junk pile, one of these may be alright for the storage.   I plan to mount it on the copper board below.

[joeqsmith]

I was looking for a test procedure that describes the test setup for multimeters in more detail and found the attached.   Section 5 covers the ESD testing.  Now, I have to believe even the UT181 would survive this test and question the point of it.  I suspect other test houses may perform it differently but really don't know.

Using the handheld as basically a moveable bench meter, I can see having the common lead connected to ground of the instruments.  In my case, this is also earthed.   I won't always use the leads supplied and some are very short.   Now it's winter, the house is VERY dry and I walk to my office (all carpet) and approach the bench.  No wrist strap and I don't touch the mat.  Rather I touch the other lead to the meter at the tip.  I was really expecting they would have one lead attached to the plain, and the other lead floating then touching the tip of the lead.  Criteria B means it must self recover.   Then I would run it in every switch setting and I would test the meter in the end to make sure the thing still works. 

[joeqsmith]

I finished my first attempt to construct a home made ESD gun.   The grill starter would put out about a 1A 5ns wide pulse was all but the open circuit voltage was around 15ish KV.  The gun starts with a regulated 4.0KV supply and I plan to again only do direct contact assuming I get something that works well enough.   

Again, my home made 2 ohm target is attached to the scope with a 26dB attenuator and about a meter of RG400.  So for example, 100mV would be about an ampere.  The standards don't really cover the open circuit waveforms.   They want 15A in that sub ns range.  Then decay to roughly 8A in 30ns and 4A in 60ns.

There is some risk playing around with this gun.  The LeCroy 64xi display will flicker then there is always the stupid USB problems.   The 64xi does not have near enough top end to see what is really going on but I don't like playing with the faster scope while I am working out the design.   So here are the first waveforms off it.  At about 60ns the scope is showing 350mV or about 3.5A.  Construction is pretty poor right now but it's already looking better than the grill starter.

I was digging into that first test report where they tested the meter without the leads.  Looking at the EN 61326-1:2013

3.11
port
any particular interface of the specific device or system with the external electromagnetic
environment
EXAMPLE See Figure 1 for an example of Equipment Under Test (EUT).
Note 1 to entry: I/O ports are input, output or bi-directional, measurement, control, or data ports.
Note 2 to entry: Within this document, ports intended to be connected with earth potential for functional reasons
(functional earth ports) are considered as I/O ports
Note 3 to entry: Within this document the protective earth port (if any) is considered as part of the power port.

5.2.4 I/O ports
Where there are multiple I/O ports, which are all of the same type, connecting a cable to just
one of those ports is sufficient, provided that it can be shown that the additional cables would
not affect the results significantly.
If not otherwise specified in more specific parts of the IEC 61326 series, electrostatic
discharges shall not be applied to inner pins of plug-in ports or cable connectors (but to
connected connectors accessible during the intended use of the EUT).


6.4.3 Performance criterion B
The equipment shall continue to operate as intended after the test. No degradation of
performance or loss of function is allowed below a performance level specified by the
manufacturer, when the equipment is used as intended. The performance level may be
replaced by a permissible loss of performance. During the test, degradation of performance is
however allowed. No change of actual operating state or stored data is allowed. If the
minimum performance level or the permissible performance loss is not specified by the
manufacturer, either of these may be derived from the product description and documentation
and what the user may reasonably expect from the equipment if used as intended.


IMO, that first reports ESD test was pointless and did not follow the sprit of the standards.

[joeqsmith]

After several more attempts, shown attached to the higher BW scope.  2 amperes per division.  It's an improvement, but getting the 15A out of it with any sort of edge is not trivial..  Starting to see why there are no home made guns out there. 

Touching the this onto my fingers, compared with the grill starter, this is a pretty good poke.   Feels more real worldish from my finger ESD experiences... 

[joeqsmith]

Much better.  2A / division, 15A peak.   

[tautech]

Nice Joe, did we never did doubt you'd get there. 

More carnage awaits.