Handheld meter robustness testing

[joeqsmith]

True-RMS (calculation) is AC coupled in the DMM IC used in the AN8002, AN8008 etc.
I thought any DC offset is ignored as part of the calculation.

But some DMM's include the DC portion if using the good old analog AD536 true-RMS converter (which costs much more than a cheap multimeter...)
Joeqsmith, didn't you already try adding a DC offset to a waveform, many posts prior?

Good memory.  Yes I did run some tests with DC but maybe not for the reason you suggest.  This was really to show the problem with the auto range where the meter shows a low AC voltage.  These meters have been the worse I have seen for this.  So as long as you are aware of that, you could work around it (add a manual range button as I show). 

In the following pictures, I have a sinewave that is fullwave rectified.  This drives the three in parallel.  I show both the AC and DC content of the ZT102 compared with the Fluke 189.   The 189 can calculate the AC+DC which obviously the Kasuntest can not.  So back to pulling out your calculator.  But it's was only $15.  I think the cheapest meter I bought with AC+DC was when Ruby Electronics was selling the CEM DT9939 for $120. 

[joeqsmith]

Video comparing the leads supplied with the Kasuntest with others I have looked at.   I also wanted to see if the modified current input would survive if the fuse was blown. 

https://youtu.be/fG61v8UgzA8

[joeqsmith]

What on earth does a home made tuning fork have to do with a hand held multi-meter?   

https://youtu.be/QBho9XD7VPQ

[bitseeker]

Cool mode switch test fixture. Having it running in the background was nice while reading the forum.

I guess this upgrades the thread to, "Handheld meter electrical robustness testing."

[joeqsmith]

Cool mode switch test fixture. Having it running in the background was nice while reading the forum.

I guess this upgrades the thread to, "Handheld meter electrical robustness testing."

You can't have a proper home lab without a Panavise.  That vise gets used for all sorts of quick little tests and such.  Very handy. 

After your comment about my drop testing and expanding my testing, I was trying to think how to one up it..  lol.  Not sure that I will add the switch cycling to my normal tests or not.  Really just trying some things out.    Some meters I have purchased, the switch design was so bad the meters did not work out of the box.  I have a friend who just had a newer meter fail and sure enough, it was the switch.

Feel free to offer any suggestions.

[kalel]

I had a meter where the switch was bad from the start. Useless. You could not even be sure in what mode you are.

I actually have good experience with the cheapo DT/Harbor Freight type meter (about $2-4 on eBay depending on model or moment). No problems with the switch even with frequent rotation (e.g. turn off after checking, turn on to check again, turn off... to preserve battery - Harbor Freight one has a power switch but eBay China ones do not). But this is different for people who really use their meters (e.g. every single day, for work). They will see switch problems much sooner.

That looks like a really nice rig to test switch duration.
If temperature is an issue with the tests (as in real use it's not likely to get things too heated), is it possible to add some pause after every x rotations?

[joeqsmith]

I had a meter where the switch was bad from the start. Useless. You could not even be sure in what mode you are.

I actually have good experience with the cheapo DT/Harbor Freight type meter (about $2-4 on eBay depending on model or moment). No problems with the switch even with frequent rotation (e.g. turn off after checking, turn on to check again, turn off... to preserve battery - Harbor Freight one has a power switch but eBay China ones do not). But this is different for people who really use their meters (e.g. every single day, for work). They will see switch problems much sooner.

That looks like a really nice rig to test switch duration.
If temperature is an issue with the tests (as in real use it's not likely to get things too heated), is it possible to add some pause after every x rotations?

That one CEM I bought would not even turn on because of the switch.  The plastic needed some adjustments with the razor.  lol.   I would expect the mechanics to give out long before any electronics (assuming normal use).  When I starting paying over $100 for a meter, I really expect the company to have the basics down, like the switch design.   Then again, I am sure they think we sell more meters if they only last a few cycles.  lol.
 
The temperature problems were a result of running it too fast.  The plastic started to get warm enough to bind.   Once it cooled it was fine.  I have a dwell time now that it sits for, along with acceleration, deceleration, max speed.   Basically, everything is adjustable with these M-Drive motors.   I really don't need it to run all that fast so normally temperature shouldn't be a problem.   

I was looking at the old Fluke my friend gave me.  That meter is pretty old and the switch still looks new.   Maybe 5000 cycles is not really enough.   It's all up in the air right now. 

[bitseeker]

After your comment about my drop testing and expanding my testing, I was trying to think how to one up it..  lol.  Not sure that I will add the switch cycling to my normal tests or not.

LOL, what will Joe come up with next?

I haven't experienced a bad switch, yet, so it hadn't crossed my mind. However, it does seem to be an issue with some meters. Flaking metallic bits inside the meter could lead to all sorts of bad outcomes. It may be a useful addition to your testing repertoire. At least it's automated so you can do other things as it runs.

[joeqsmith]

After your comment about my drop testing and expanding my testing, I was trying to think how to one up it..  lol.  Not sure that I will add the switch cycling to my normal tests or not.

LOL, what will Joe come up with next?

I haven't experienced a bad switch, yet, so it hadn't crossed my mind. However, it does seem to be an issue with some meters. Flaking metallic bits inside the meter could lead to all sorts of bad outcomes. It may be a useful addition to your testing repertoire. At least it's automated so you can do other things as it runs.

Any metallic flakes between the contacts would effect how the meter handles the surge tests.  If it's bad enough, I could see it having an effect on the normal operation.   

The problem I see with running a test like this is that its destructive.  I can't run it before I run my other tests and many times, the switches are damaged from my other tests so I can't really run any sort of cycle testing afterwards. 

In the meantime, someone asked about running a UT61. 

https://youtu.be/1h6UaF_SwKs

[Crumble]

Didn't the Kasuntest you originally ran have some kind of lubrication on it? I'm actuaaly quite surprised both meters you tested seem to be near unaffected by so many cycles. I'd be worries about the vias under the wipe contacts, but given the limited wear this probably won't ever be an issue before the meter (or the user) dies.

[joeqsmith]

Didn't the Kasuntest you originally ran have some kind of lubrication on it? I'm actuaaly quite surprised both meters you tested seem to be near unaffected by so many cycles. I'd be worries about the vias under the wipe contacts, but given the limited wear this probably won't ever be an issue before the meter (or the user) dies.

I have bought four ZT102s and one AN8008.  None of these had any sort of lubrication that I saw.  I have not looked at that last ZT102.   I did apply some lubrication to the second ZT102's ball detents, along with swapping out the springs from the first unit to try and get the switch to have a better feel to it.  I did the same thing to the third unit. 

Again, I would not read much into these initial tests.  The meters have all been apart and badly abused.  It's possible for example that when I forced all that current through the contacts I softened them and changed their tension.   Maybe now they are pushing down with less force and this is why there is little wear.  I have no idea nor did I care.  Thinking a virgin meter would behave the same would make no sense what so ever.   

I have been looking for manuals that call out the number of cycles they rate their switches to.  I have yet to find anyone providing this detail.  Strange and you would think it would be common. 

[stj]

my 102 had clear grease smeared/sprayed onto the pcb contacts,
but the plastic detents had very small grease traces - like it had been applied to the balls rather than the plastic.
maybe they did it to hold the balls to the springs during assembly. 

[joeqsmith]

That's strange.  But then again, ever meter I looked at had a different xtal and two have the VAC frequency/duty cycle and two do not, plus different springs.  Must be a total crap shoot with them.

Is yours an actual Kasuntest ZT102 or some other branded version of it?  I would not mind seeing a clear picture of the grease in the switch area if possible.   

[stj]

mine is ANENG badged,
cant do pics because i re-greased it.
it has the freq/duty on it btw, but not printed on the case.

[stj]

btw, are the switch contacts the same as centech / harbour-freight meters?

i have a second 102 from someone who lost 2 contacts while messing in it after they managed to blow up the transient suppressor somehow!!

[joeqsmith]

Thanks anyway.  I only had that one ANENG AN8008. I wonder if they removed the grease as a cost saving measure.  Really, why not? 

I think that PTC was only rated for 500V.  Still, under normal use, it would not be a problem as most people don't try and read voltage with the resistance mode, or when the meter is off. 

From all of the meters I have looked at, it looks like there are only a few variations of switch contacts.  Shown are the Kasuntest next to a HF free meter.  Note that I cycled the HF meter and the contacts are a bit worn but I've seen much worse. 

 

[stj]

thanks, they look compatable.
just have to find an old centech now.

[stj]

it's not the ptc, it's the bi-directional diode on the left of the battery box that protects the current range afaik from overvoltage.
meter runs fine without it using my other casing.

i will fit a new one though - and probably up the fuses to 20mm ceramic "FF" rated ones.

[joeqsmith]

The TVS makes much more sense than the PTC.  With the fuse they have in there, I would not be surprised with a quick measurement of how much current comes out of a house outlet may do it in.   That or replace that tiny fuse with some wire.... 
lol.

[stj]

the guy i got it from was very reluctant to tell me what he did, but from some comments about the meter that slipped out,
i think he was trying to take a low current reading from the mains!!
obviously didnt read the manual where it states 35v max!!   

[joeqsmith]

Makes sense.  When I was researching Gossen products I read a post where a guy damaged a new meter they had bought at work I believe with the current input and AC mains.  It may be more of a problem than people are aware of.  If you watched that last video I made where I tested the current inputs on the standard ZT102 and AN8008 compared to the one I modified, that fuse Dave provided makes all the difference in the world.   

But again, to be clear, I doubt that would be a problem with low voltages.  So a hobbyist playing with 5V and less digital logic, it's should be much less of a risk damaging the meter.  Even the unfused free HF meters may be just fine.   Then again, this is not the group that should ever be concerned with any of the low energy surge tests I run.  These are the people who tell me how my tests far exceed what these meters would ever see.  Let's see todays post was "... and all this high voltage warnings are also useless - who measures above 1000v with such meter,..."  Or they tell me how I am doing direct discharges with capacitors into these meters and how stupid it is.   Or they watch them and decide because they just saw their meter take a 10KV hit that it could be connected to a MOT secondary.

[stj]

well, some people do some extreme things when they have no choice.

i have read of a guy checking the 3KV output of a fence charger he repaired,
first with a fluke - killed it!
then with a low end uni-t that actually gave him the reading!!!!!

another guy testing the neck socket of a crt without knowing how high the focus voltage is.

so low current HV is more "available" than people realise.

[Crumble]

Didn't the Kasuntest you originally ran have some kind of lubrication on it? I'm actuaaly quite surprised both meters you tested seem to be near unaffected by so many cycles. I'd be worries about the vias under the wipe contacts, but given the limited wear this probably won't ever be an issue before the meter (or the user) dies.

I have bought four ZT102s and one AN8008.  None of these had any sort of lubrication that I saw.  I have not looked at that last ZT102.   I did apply some lubrication to the second ZT102's ball detents, along with swapping out the springs from the first unit to try and get the switch to have a better feel to it.  I did the same thing to the third unit. 

[...]

What is it then that you are mentioning here at 9:21 in this video? There was definitely something there.

I have disassembled mine to check for any residue, but I found the board to be completely clean. I did however use the opportunity to put a tad of grease in the detent race. There seems to have been a very minimal amount of it already present, but they supply ball bearings and steel parts that way quite often to prevent corrosion.

[joeqsmith]

Didn't the Kasuntest you originally ran have some kind of lubrication on it? I'm actuaaly quite surprised both meters you tested seem to be near unaffected by so many cycles. I'd be worries about the vias under the wipe contacts, but given the limited wear this probably won't ever be an issue before the meter (or the user) dies.

I have bought four ZT102s and one AN8008.  None of these had any sort of lubrication that I saw.  I have not looked at that last ZT102.   I did apply some lubrication to the second ZT102's ball detents, along with swapping out the springs from the first unit to try and get the switch to have a better feel to it.  I did the same thing to the third unit. 

[...]

What is it then that you are mentioning here at 9:21 in this video? There was definitely something there.

I have disassembled mine to check for any residue, but I found the board to be completely clean. I did however use the opportunity to put a tad of grease in the detent race. There seems to have been a very minimal amount of it already present, but they supply ball bearings and steel parts that way quite often to prevent corrosion.

I really don't know what that stuff was.   It almost looks like when the board was washed that something dripped down.  Normally with grease it will not just wipe off.  It smears and it is slick.  I've seen a few where they use it and it's always been more translucent and applied around the contacts, not dripped across the board like this one.  I have not looked at that 4th unit to see if there was anything in it. 

[joeqsmith]

well, some people do some extreme things when they have no choice.

i have read of a guy checking the 3KV output of a fence charger he repaired,
first with a fluke - killed it!
then with a low end uni-t that actually gave him the reading!!!!!

another guy testing the neck socket of a crt without knowing how high the focus voltage is.

so low current HV is more "available" than people realise.

It seems I read one about a fencer as well but I don't recall the Fluke/UNI-T part.  It may have been a whole different case. I imagine this sort of thing happens more frequently than what is ever posted. 

I have a friend who was doing something similar trying to read the primary side off the coil in a lawn tractor.   The first two meters he tried would not give a stable reading, so he used one of the UT210E clamps and it worked.   No meters were damaged in that case.

I play around a fair amount with low current higher voltages which is partly why I am interested in running the meters this way.   I would never think of hooking up a meter to a fencer but then again, I did try that fly swatter after Scott posted about it.    

Here's this morning's comment for the day:

Your video actually shown that this dirt-cheap device is at very least conform with CATII/300, means it's compeletely safe to be used in electrical household.
According to spec CATII/300 it should be capable to withstand upto 2500V impulse voltage. Note that It said: impulse,  a voltage spike, not a contstant current.

Why does he feel my tests show the meter is completely safe?  People can't read, don't want to take the time to read or they just like to state their opinions no matter if they know something about it or not.     I can only guess what that last sentence means.   It's too bad these people won't post their opinions in this forum.  If you could actually get some constructive dialog (rare), it may actually help the group.