Killed one of the new 3 dollar 40 cent multimeters
OK, they are only 1 kV, and I went to 1900 V and higher. So this is the third dead multimeter, it shows very erratic readings now on all ranges, chip CMOS isolation pierced I think, actually it may have seen as much as 2700 V and that while changing voltage ranges.
So, anyways, I have some nice analog 100 uA (IIRC) huge meters somewhere in the attic, will add a resistor and make an analog HV meter for this PMT stuff. Or maybe some HV attenuator box for the second (and last Chinese meter). sniff sniff. At least now I have a spare 9 V battery, See good in bad :-)
High voltage, the death of most DMM's? I killed a 'good' ~$50 DMM many years ago when I hooked it up to the spark from an old 5 HP lawn mower engine that wouldn't run. I was 'convinced' that the spark/ switching circuitry was no good. In retrospect a little resistor string could have saved me from kicking myself all day!
If you work with HV much, forget the meter- get yourself a Fluke 80K40 probe and you will be more likely to survive working with high voltage at low Z.
You don't check spark with a meter under any circumstances, unless the equipment is specifically designed for that, and even then, it's usually a capacitive pickup. The way to test for spark is to pull the wire off the plug and have your little brother hold the clip (or cap) about 1/4" away from the block (or even the plug contact), pull the rope, and _see_ if it sparks.
If you don't have a little brother, then you can use one of those phenolic "fuse puller" thingies, or any insulated holder of some kind.
On a sunny day (Tue, 8 Nov 2011 08:07:17 -0800 (PST)) it happened George Herold wrote in :
What I think happened is that I switched ranges, while still voltage in the HV capacitors. In these simple PCB range switches then the CMOS input possibly gets the full current via the series resistor, but could be anything else of course.
I looked in the attic, found 2 huge analog meters, but those turn out to be 1 mA fsd. That is too much load to measure stuff like this. So, went to ebay and ordered a 50 uA analog multimeter for 6 dollar 55 inclusive shipping: ebay nr 160573395515 from China. Cannot even buy a stand alone meter for that here. I also ordered 3 extra digital multimeters, the same as the other ones, 3 dollar
Yeah, I did that (pulled plug, reattached the HV, grounded the other end and looked for a spark... I'm not a complete idiot... just a sometimes idiot.) Of course then you have to test and make sure the plug is OK too.
I recently got mine( having read about it here) I just love the big display for my tired old eyes. Only downside is the DC current range- only goes down to 2 mA whereas my old faithful went down to 200uA. I see there is a better version 9501A that does 20uA...but I haven't seen one on EbayUK ... yet.... The continuity buzzer is PATHETIC(sounds like a squeeking mouse).... I'll have to sort that!
Harbor Freight usually has little cheap multimeters for as little as = $1.99=20 each. I have several, and some still have the original battery, which = alone=20 is almost worth the price. Except for the AC ranges, they're pretty = good.=20 For AC they just use a series diode.
I have two or three electrostatic voltmeters that I have used for high=20 voltage measurement. I think the smaller ones, in square bakelite=20 enclosures, are 2.5 and 5.0 kV (AC or DC). The larger one is in a wooden =
case with a bakelite arm that (I think) moves into several positions for =
multiple ranges up to 10 kV, and I think there are some that go as high = as=20
100kV. Something like these:
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(like the one = with=20 curved glass, but in wood box)
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I also have a bunch of high voltage resistors, made of glass tubes with=20 silvered ends and a spiral resistive element, 300 Megohm (IIRC). = Originally=20 used in "hot sticks" which are bakelite tubes containing the resistors=20 stacked in series and an analog meter in the handle. I also have the = tubes,=20 from surplus inventory I got 20 years ago. Something like these:=20
"P E Schoen" wrote in news:BxFuq.17021$ snipped-for-privacy@newsfe13.iad:
FYI,the cheap Harbor Freight DMMs only have 1 Megohm input Z. I took mine apart once.Thought about rebuilding the divider string to
10MegR. :-) Also,the input connector jack solder joints crack at the PCB,cause intermittents.
Lastly,and most importantly,the first HF DMM I bought was VERY inaccurate,read a 1.5V battery at nearly 2 volts. I returned it for a more accurate replacement. Of course,my local HF store is only a block away. :-)
It irks me that I didn't buy that used Fluke 515A meter calibrator for $100 when Skycraft Surplus had one for that price. :-(
Which is exactly why I want at least 4.5 digits and 20A range. I never have to use the fused ranges ;-)
--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
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I killed a Beckman DMM many years ago when hookED it to THE horizontal output tube in a B/W TV, can't remember the DMM model but it can read capacitor down to few pF range
I think I hooked it to the booster gate, not the anode ;(
The 20A range IS fused, if only with a section of pcb. A friend recently passed a RatShack 22-175 "3-2/3 digit bench DMM" to me for repair or dumpster. It was under-reading on all voltage scales and essentially didn't respond on any current scales. This has (replaceable) fuses for eveything except the 10A range.
A section of track near the COM terminal, where it necked slightly to pass a component pad, had been cremated. It was probably 7mm wide at that point. When that "fuse" was replaced everything returned to normal.
On a sunny day (Thu, 10 Nov 2011 13:57:26 -0800 (PST)) it happened halong wrote in :
I killed the left channel of my Trio anlog scope by touching the booster anode. I then used the right channel to scope the scope, found a defective chip, called the importer, told the story, and they send me a new chip for free. This scope was bought in 1979, and I am still using it every day. So, 32 years on the counter... That is quality.
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