Handheld meter robustness testing

[kcbrown]

With the right firmware ... this meter looks like a winner!

Who needs a Fluke 87V?

(apart from people who want to get past building security guards)

Because the 87V is likely to survive better if you whack the security guard over the head with it?   




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[joeqsmith]

My TPI194II was damaged from the stupid AC line test.  One of the symptoms was the resistance with an open was a few Meg.  I had looked into repairing it but found that the problem was two pins of the front end IC were leaking a lot of current.  I tried to buy a new IC but could not find a source. TPI had offered to replace the meter but it really was not their fault the meter was damaged.   

I looked at again today.  Basically, meters will normally have a multiplexer stage to switch the resistors for the attenuator.  The resistors are normally off chip.  The resistors can normally be switched at all the different voltages available to the IC.   On this IC, when a resistor is not selected, the output goes high Z. What happened was it was pulling these two pins low (to the battery ground).  So, I added a series diode and trimmed the resistors to compensate for the loss.  It does not work great but at least now those two pins are not dragging the input down.


Here it is with an open set of leads.
 
 

[joeqsmith]

All the functions basically work. Temperature drift would be a problem and really, its a pretty crappy way to bring it back to life.  Why they did not clamp this input, no idea.  It's a fairly expensive meter. Very solid case design.  Has some pretty nice features.  Even certified.

[joeqsmith]

Thermal couple input, capacitance and AC+DC with the tri-display.   The meter uses TH axial parts for the attenuator.  One of these was replaced with four resistors and a diode to get it trimmed in.  The other catch is that the because the damage pins can no longer sink, you loose the divider function for the voltage mode.   The meter will not display the correct voltages once the input is above 50V (50K count meter).   

[joeqsmith]

What to do with a damaged pre-production meter?  One day, someone is going to look back on this and say, if they had only left it, it would be worth $1,000,000 on eBay but because of the unoriginal condition, it's now worth $0.01 

Lots of work to do.

[ci11]

Hi Joe,

Here is something a little different you should tear down and thoroughly test, the $65 Kill A Watt PS-10 power strip.

It is a normal Kill A Watt with some additional "smarts" built in that appear to be pretty useful for any bench on a budget. Its claims to have a "zero-crossing soft start", settable current limiter, leakage current measurements and a 10-tap output strip for up to 18A is begging your lab to get it the thumbs up. Things I'd like to know are: does it protect as claimed, is it accurate, can it be modded to keep the backlight constantly on.

This has the makings of interesting match between a useful smartie-pants power accessory and the latest word in electrical safety testing!

[joeqsmith]

Hi Joe,

Here is something a little different you should tear down and thoroughly test, the $65 Kill A Watt PS-10 power strip.

It is a normal Kill A Watt with some additional "smarts" built in that appear to be pretty useful for any bench on a budget. Its claims to have a "zero-crossing soft start", settable current limiter, leakage current measurements and a 10-tap output strip for up to 18A is begging your lab to get it the thumbs up. Things I'd like to know are: does it protect as claimed, is it accurate, can it be modded to keep the backlight constantly on.

This has the makings of interesting match between a useful smartie-pants power accessory and the latest word in electrical safety testing!

I did look at a killawatt some time ago just to see if the numbers they put out were in the ballpark.  Actually, it seemed to do a fairly decent job for the price.  I am sure it could be modified to do what ever you like given enough time, money and brain power.   

I would really have no way of knowing if it could protect as claimed.  For this you really need to look for someone like UL to test it. 

I wonder about the zero cross soft start.  It sounds VERY complex.  Just zero cross detection in general can be a bit of a problem.  There is equipment to test this sort of thing but again, it's way outside of anything I am doing with the meters.   

[ci11]

Gotcha.

Here is the exact verbage on 'zero crossing" from the Owner's Manual:

"Pressing the ON key will turn power on to the 10 built-in outlets at once. The unit features a spike-free switch function which activates at zero-crossing and will present clean power to your connected appliances. The ON key will illuminate in green. The unit will measure power and the function keys and LCD display will operate."

[joeqsmith]

Could just be a TRIAC with a zero crossing driver. 

[SeanB]

What I was thinking, a simple zero cross snubberless SSR relay in there, nothing more. Wonder what the leakage current of the switch is, those can be a big nuisance with small loads that will either never actually be turned off ( thus negating any power savings) or worse that sit in a voltage level that will either cause a brownout or regular malfunctions that seemingly are random, to totally blowing up the supply as it tries to regulate the switch on time past 100%.

Then also wonder just what they are using as a power supply, and how much it also uses, and how well protected it is as well.

Joe, just for a lark, can you put a few USB wall warts ( not the cheap ones, but ones from reputable manufacturers, because we all know how the cheap ones will fail anyhow) across your line simulator and see what it takes to kill them. My guess is that almost all of them will fail 2kV, but just how badly they do this, and how much they smoke doing so. Most will probably work fine with your test voltage, being universal input devices. You will just need a sacrificial USB voltage monitor and a resistor to draw 100mA to 500mA out of them during the test. Pretty much how they behave in transient conditions, and what a simple mains transient like a motor disconnect on the same branch circuit will affect them.

[joeqsmith]

I wonder if they don't have a mechanical switch in there for the leakage.   Note the mechanical breaker is still present but I suspect turn off the TRIAC when the current reaches the set point (calling that their programmable breaker).

I did not transient test the killawatt I had but I did have it apart.  Cheap, like you would expect for the price.   

Joe, just for a lark, can you put a few USB wall warts ( not the cheap ones, but ones from reputable manufacturers, because we all know how the cheap ones will fail anyhow) across your line simulator and see what it takes to kill them. My guess is that almost all of them will fail 2kV, but just how badly they do this, and how much they smoke doing so. Most will probably work fine with your test voltage, being universal input devices. You will just need a sacrificial USB voltage monitor and a resistor to draw 100mA to 500mA out of them during the test. Pretty much how they behave in transient conditions, and what a simple mains transient like a motor disconnect on the same branch circuit will affect them.

I would guess they fall under the generic case and are only required to be tested at 1KV line-to-line.   

Again, that sub 20J I test with is basically nothing.  I don't see it ever causing a meter or other device to explode or put out much for smoke.   Really what you would want to do is run these on a real combo generator if you wanted to see something more like the Fluke multimeter videos where they show the cases coming apart.  This is nothing close to what I have setup.   

[SeanB]

True, but you do have a good audience, and it will be a good thing to show that cheap and nasty really is that, even with limited energy. I think the saving grace for most products these days is the thin wire they use, which acts as an impromptu fuse when the thing fails short circuit. As the fuse is often the thing "designed" out by the cost cutters, and the wire is also "value optimised" to be as thin as possible and as low grade copper as possible this probably is the only thing keeping the fire rate down.

[floobydust]

What about multimeters crashing when connected to HV, to take a voltage measurement?

I've seen a few where the display flickers or the meter reboots when touching the probe to high voltage.
There is a small arc to the probe with the multimeter's input capacitance and I think the EMI burst is too much. Happens consistently around 400-600VDC up, tiny arc.

Long time ago 2002 Fluke had that problem 177,178,179 and did a recall over the time to reboot making a dangerous situation. Cheap meters never recover, they just look stoned and read garbage.

[joeqsmith]

What about multimeters crashing when connected to HV, to take a voltage measurement?

I've seen a few where the display flickers or the meter reboots when touching the probe to high voltage.
There is a small arc to the probe with the multimeter's input capacitance and I think the EMI burst is too much. Happens consistently around 400-600VDC up, tiny arc.

Long time ago 2002 Fluke had that problem 177,178,179 and did a recall over the time to reboot making a dangerous situation. Cheap meters never recover, they just look stoned and read garbage.

I run every meter I look at close to 900 VDC and do not remember ever seeing any problems like you describe with flickers or reboots.  This includes the free meters from HF. 

Most of the meters I look at will have maybe a MOV which makes up the majority of input capacitance. I have only seen one meter where they had a place holder to put a MOV right across the inputs and it was not populated.       With DC, I am not sure what this EMI burst is you mention.  Maybe help me out there.    For this flicker, lockup problem, you would need to provide a list of meters you have seen this with.

[EEVblog]

Is len = 0 the reason the spreadsheet shows the interval to be zero seconds?

Yes.  Setting it to 1, shows 1 second and it seems to record at that rate.  I tried 999, interesting is that it must wait the 999 second before recording the first time rather then recording the first sample once logging is started, then waiting.

The idea of the "zero" setting was to let the logger record at the max rate of the ADC (5/sec nominal, but will change with the range). otherwise it's in seconds.

[joeqsmith]

Spent a fair amount of time today looking at the 121GW's circuit board.  That has to be the most heavily populated meter I have looked at. 

[joeqsmith]

It's been a long time since I have really done some major damage to a handheld meter.  Even with all the problems the Gossen has, the one thing it has going for it is it is very robust.  The we have the pre-production 121GW that was damaged before I had a chance to turn things up.   I'm pretty sure this next meter is going to give us a show.   It's another RadioShack.  The last  RadioShack meter I looked at came from 5Ky and that thing was very solid.    Some of these low cost meters have been very impressive.   
 
Catalog number 22-813.  Much smaller than the 121GW.  It's one of those meters that share the voltage input with the current.  Maybe it has some glass fuses in there as well. 

[MacMeter]

Look forward to the video!   

[sleemanj]

Manual says a single ceramic fuse
https://www.manualslib.com/manual/605149/Radio-Shack-22-813.html?page=21#manual

... Maybe I should have spoiler'd that :-)

[xrunner]

It's been a long time since I have really done some major damage to a handheld meter.

Joe did you get my PMs? I sent you two and never heard from you. 

[Vgkid]

Nice job Joe.  Will you go over your mods once the meter is released?

[joeqsmith]

Nice job Joe.  Will you go over your mods once the meter is released?

I will not be releasing any details about the pre-production meter's design.  Keep in mind that the meter was already more robust than Fluke's golden standard, the 87V.  There may be no reason to improve it if that is what people feel is good enough.  I have been providing Dave with feedback as I have been going over the meter.  I believe they plan to make some changes to address some of my concerns.   

I'm looking forward to seeing the final design.

[Fungus]

Am I correct in imagining that the transistors that failed in the Fluke87 are a voltage clamp as shown at the start of EEVBLOG #1000?

[Fungus]

One thing I've been meaning to ask, and this seems an appropriate place, is:

What's the difference between "CAT III 1000V" and "CAT IV 600V"?

The transient voltages and source impedances are the same (8000V, 2 Ohms).




(from http://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdf )

[3db]

@Fungus
The working voltage.

3DB