Handheld meter robustness testing

[SeanB]

How about doing the high voltage testing one time with the bare board in the case, with a mirror ( well insulated) so we can see both sides of the board at the same time to show where the arc over occurs.  Need to have the cover on for this, and latch it down well for your own safety, as it will make copper vapour as it blows.

[joeqsmith]

The mirror is an interesting idea.  Cheaper than a second camera! 

I don't talk about safety much when I run these tests.  The energy levels are normally so low, there is very little risk.  The generator has a fair amount of safety features designed in as well.  The half cycle generator adds a little more risk.  The cameras are about two and a half feet back to avoid any damage to them.  I am no where near the device I am testing when they go off.    I keep the output shorted up until I am ready to run the test.  If I test with fuses, light bulbs or other things with glass I will normally cover them up to at least contain the fragments.  Once the transient has fired, I shut the system down and short the outputs before doing anything else.  Running an open board would pose less of a risk than having something that can contain the pressure, like my fuse powered rocket.   

[joeqsmith]

Some things just never get old.....    Video is finished with some bonus material.  About a half hour total. 

[Muttley Snickers]

Joe just recently posted another video on his Youtube channel so here it is linked below.   

[joeqsmith]

Sad to see the pen meter fail with the 220V line test but on the plus side at least it survived the grill starter unlike the vast majority of UNI-T meters I have looked at. 

We will see what Fluke has to say about the VHS tape.   

In the mean time, I have a little nicer analog meter I plan to look at next.  It's a Ketai Instruments KT-7050 sold under the Tekpower brand.  I may see if the schematics are available and just see if I can made it more robust rather than just damaging it. 

[joseph nicholas]

My cheap meter stopped working after only 9 months on all its voltage scales. I decided to buy a MF-47 analogue miltimeter kit.  At least if it gets damaged I know it would be easy to fix if needed from handy through hole parts.  It will probably be my go to meter of choice for trouble shooting.  I was inspired to do this after seeing the abismal quality of construct of the digital I bought.  The circuit board looked like it was stored in a wet basement for several years.  It was corroded and mouldy.  I bought it as new.  When I viewed the you tube video of a teardown of the same meter the internals were nothing like the video showed.  The exteriors were exactly the same.  When I got the meter the  a wire fell out of one of the probes for no reason.   

[3db]

@Joeqsmith
Take a bite out of UNI-T 

[joseph nicholas]

I found mine on ebay.  I haven't gotten the kit yet to assemble but I'll tell you how it goes.  This is perhaps the uglyest multi-meter ever made but it has a bale, and what could be some decent test leads for a change.  I paid something like 10.00usd for it but after I paid the site raised the price so go figure.  While I am waiting for the analog meter I tried to fix the cheapy.  It too has some schematics on line but unfortunatly no joy.  I doubt I cooked the chip because the thing still counts and works in the other modes.  Eventually I know I will fix it and it too should last. 

jnicholas

[joeqsmith]

This is perhaps the uglyest multi-meter ever made but it has a bale, and what could be some decent test leads for a change.
jnicholas

   It looks cleaner than that first analog meter I tore apart.  If that wasn't ugly enough, I really made a mess of it with all my mods.   
Looking forward to seeing the kit. 

[rsjsouza]

Joe, that was a pretty cool mushroom in the high speed camera.
Despite it is stronger than your UNI-Ts, I can't help but imagine this is actually much more unsafe than a DMM on the table: the potential to burn the hand that holds the pen while this happens is pretty high.

Anyways, that was another excellent video! Thanks for doing this.

[joeqsmith]

Joe, that was a pretty cool mushroom in the high speed camera.
Despite it is stronger than your UNI-Ts, I can't help but imagine this is actually much more unsafe than a DMM on the table: the potential to burn the hand that holds the pen while this happens is pretty high.

Anyways, that was another excellent video! Thanks for doing this.

Thanks for the compliment.   I do like that camera.  It captures things that we just don't see with the slower one. 

I get what you are suggesting about how this meter could be less safe than the UNI-T's even though it held up a little better.  Keep in mind, while the grill starter did not end it's life, that little rectified AC waveform did.  IMO, its a pretty poor design.  We can look at the mushroom cloud and think it's worse but I really don't know.  The energy is just so low I am really not sure what it tells us.  If we ran fuse tests on every meter using an actual CAT III line, what would actually happen?  Meters we think look safer may indeed come apart with some a much more dramatic effect.   I just don't know.   We need to leave safety to the experts. 

When I made those couple of videos showing how stupid it is to jumper out an HRC fuse, at one point I stuck in some 28 AWG or something of that sort.  When I hit it with my generator, I did not even have enough energy to blow that wire.  It's pretty pathetic relative to photonicinduction's sort of destruction.   

[rsjsouza]

Well, my reason to assume the relative safety levels is based on the distance between the operator's body and the source of the explosion...

However, there's always a chance the dial of the meter on the table comes flying after the event and hits the operator in the head... 

[joeqsmith]

Well, my reason to assume the relative safety levels is based on the distance between the operator's body and the source of the explosion...

However, there's always a chance the dial of the meter on the table comes flying after the event and hits the operator in the head... 

I'm not sure I follow.  Are you suggesting because it is a pen meter that the operator would be holding it where a meter with leads, they would be holding the leads and not the meter and this means the pen is less safe?  There could be some merit to that. 

That knob flew about 8' across the room and hit the wall. 

[rsjsouza]

Well, my reason to assume the relative safety levels is based on the distance between the operator's body and the source of the explosion...

However, there's always a chance the dial of the meter on the table comes flying after the event and hits the operator in the head... 

I'm not sure I follow.  Are you suggesting because it is a pen meter that the operator would be holding it where a meter with leads, they would be holding the leads and not the meter and this means the pen is less safe?  There could be some merit to that. 

Joe, yes I am suggesting that.

One ergonomic aspect that I noticed with the pen DMM I have is that it is impossible to do the "hand on the pocket" rule if measuring high energy circuits, unless an alligator clip on the negative side is used. With a traditional table DMM you can also hold both probes in one hand. Anyhow, I digress.

That knob flew about 8' across the room and hit the wall.

I have experienced situations where flying remnants of average energy short circuits (mains) were targeted at me. Fortunately I used glasses at the time, which saved my eyes from any damage.

[joeqsmith]

That make sense.  There was a couple of clips included with the last meter that will fit over both ends.   In practice, I would never use a meter like this in the first place.  One wrong click on the dial and they are in current mode.   

[joeqsmith]

All tucked in and waiting for things to get stable....

[joeqsmith]

Attached shows the previous data as well as the test I ran today.   Note that instead of running them from -10 to 40C, I ran them from -20 to 60C.   I also changed from a 1V reference to 1mV.  We can see running with 1mV we can now actually get some idea about their drift. 

While I have heard how poor the UT61E was, it is not as bad as the $300 Extech! Now again, I have been inside that Extech but I very much doubt anything I have done would have changed its TC.   The UT181A that I damaged, repaired, modified the PCB out performed my BM869s.   

[joeqsmith]

Comparing 5KY's UT61E with mine. Even thought the two meters are similar, I have a feeling UNI-T belongs to a resistor of the month club.   The JML datasheet shows +/-200ppm.  Not sure what the others are.  May just swap out the few passive parts and see what difference it makes.

[joeqsmith]

Can you make a $50 UT61E more temperature stable than Dave's BM235 without buying an expensive reference?  What about making it even more stable than the BM869S and keep the parts cost under $1.00? 

Stay tuned for the next video where I will show how I pull it off.

[joeqsmith]

Here you go, for less than 35 cents in parts in single qtys, the UT61E takes on my two Brymen meters.   

[Vgkid]

Best Eleotron, couldn't even afford a "c".

[joeqsmith]

2017 is shaping up... 

[Muttley Snickers]

2017 is shaping up...

And shipping out by the look of it, what's in the box ?.   

The suspense is killing me meters.   

[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.