On Thu, 02 Jul 2020 06:45:42 +0100, Cydrome Leader <presence@mungepanix.com> wrote:

> In sci.electronics.equipment Ralph Mowery <rmowery28146@earthlink.net> wrote:
>> In article <rdecuc$m73$1@reader1.panix.com>, presence@MUNGEpanix.com
>> says...
>>>
>>> > So should I assume the cheaper ones are lying? Or have they just made a rough estimate adding the two errors?
>>>
>>> might be both. I dug out my first DMM, a Wavetek DM2, circa 1990s. It might
>>> have been from a raffle or something like that.
>>>
>>> The DC voltage specs range from 0.8% +1 digit (not bad really) over to the
>>> AC ranges which are "1.2% RDG +10 Digits". If I had new leads, I'd trust it
>>> with outlet voltage, but would stay away from 208volts. The meter has 3.5
>>> digits or max display of 1999. I'm figuring a real 100volt AC reading could
>>> be 99 to 101 plus another error of +/- 1 volt for the 10 digits tolerance
>>> on the display or count. so 100volts from your Japanese outlet reference
>>> might read 98 to 102 volts. So while in the ballpark, it's better than you
>>> can read off a Simpson 260 meter in the AC voltage range. I could be wrong
>>> on this too.
>>>
>>> It's a pretty decent meter for poking at DC circuits for the tens of
>>> dollars is must have cost when new.
>>>
>>>
>>
>> It seems that maybe due to modern manufactoring the meters are more
>> accurate than they were 20 years ago. I bought some DC voltmeters from
>> China. They display 3 digits. They read from 0 to 99.9 volts. I coulg
>> get 4 of them for less than $ 15 including the shipping. I hooked all 4
>> of them in parallel with a Fluke 87 . Three of them tracked right along
>> with the Fluke with the last digit sometimes being one high or low from
>> 0 to 24 volts. The fourth one was off by an average of 2 on the last
>> digit. I found an adjustment screw on the back of the meter and tweaked
>> it and re ran the test. It then fell in line with the other meters.
>
> Have you run this test with AC? That seems to be where the wheels come
> off. I brought up this thread to a friend and he mentioned his quest to
> repair some sort of HP true RMS meter that uses a thermocouple and heater
> to properly measure complex waveforms. I can't even guess how slow such a
> meter might be.

How well do these things work measuring dodgy waves like from a cheap UPS or invertor?

>> I had 3 or 4 of the Harbor Freight 'free' multimeters. The ones that
>> usually sell for around $ 5. They seem to be reasonable accurate for
>> the money. Plenty accurate for the home user to test things around the
>> house. I do admit that the safety issue of putting them across the 120
>> or 240 volt power wires is somewhat doubtful. I sure would not use one
>> where I worked to put across the 480 volt 3 phase system that is fused
>> with 200 amps.
>
> I'm pretty timid with anything upstream from a plain outlet.

I've replaced outlets (240V, not the namby pamby USA stuff) without turning off the power - other outlets on the same circuit were being used in the office and I saw no point in interrupting them.

Just keep your fingers off the metal things and don't short stuff together. Wear goggles and gloves if you want to be a girl about it.

> I had an
> edison base fuse burst in my hand once. Never seen one come apart before.
> It was just a 120v lighting circuit, but right off the service panel.
> There's way more excitement near those things.

Try shorting two phases together with 500A cables. That causes lots of smoke, a fire alarm, 3 fire engines, and a visit from the power company. Do not ever employ Irish electricians.

In sci.electronics.basics Commander Kinsey <CFKinsey@military.org.jp> wrote:
> On Thu, 02 Jul 2020 06:45:42 +0100, Cydrome Leader <presence@mungepanix.com> wrote:
>
>> In sci.electronics.equipment Ralph Mowery <rmowery28146@earthlink.net> wrote:
>>> In article <rdecuc$m73$1@reader1.panix.com>, presence@MUNGEpanix.com
>>> says...
>>>>
>>>> > So should I assume the cheaper ones are lying? Or have they just made a rough estimate adding the two errors?
>>>>
>>>> might be both. I dug out my first DMM, a Wavetek DM2, circa 1990s. It might
>>>> have been from a raffle or something like that.
>>>>
>>>> The DC voltage specs range from 0.8% +1 digit (not bad really) over to the
>>>> AC ranges which are "1.2% RDG +10 Digits". If I had new leads, I'd trust it
>>>> with outlet voltage, but would stay away from 208volts. The meter has 3.5
>>>> digits or max display of 1999. I'm figuring a real 100volt AC reading could
>>>> be 99 to 101 plus another error of +/- 1 volt for the 10 digits tolerance
>>>> on the display or count. so 100volts from your Japanese outlet reference
>>>> might read 98 to 102 volts. So while in the ballpark, it's better than you
>>>> can read off a Simpson 260 meter in the AC voltage range. I could be wrong
>>>> on this too.
>>>>
>>>> It's a pretty decent meter for poking at DC circuits for the tens of
>>>> dollars is must have cost when new.
>>>>
>>>>
>>>
>>> It seems that maybe due to modern manufactoring the meters are more
>>> accurate than they were 20 years ago. I bought some DC voltmeters from
>>> China. They display 3 digits. They read from 0 to 99.9 volts. I coulg
>>> get 4 of them for less than $ 15 including the shipping. I hooked all 4
>>> of them in parallel with a Fluke 87 . Three of them tracked right along
>>> with the Fluke with the last digit sometimes being one high or low from
>>> 0 to 24 volts. The fourth one was off by an average of 2 on the last
>>> digit. I found an adjustment screw on the back of the meter and tweaked
>>> it and re ran the test. It then fell in line with the other meters.
>>
>> Have you run this test with AC? That seems to be where the wheels come
>> off. I brought up this thread to a friend and he mentioned his quest to
>> repair some sort of HP true RMS meter that uses a thermocouple and heater
>> to properly measure complex waveforms. I can't even guess how slow such a
>> meter might be.
>
> How well do these things work measuring dodgy waves like from a cheap UPS or invertor?

Probably perfectly.
>>> I had 3 or 4 of the Harbor Freight 'free' multimeters. The ones that
>>> usually sell for around $ 5. They seem to be reasonable accurate for
>>> the money. Plenty accurate for the home user to test things around the
>>> house. I do admit that the safety issue of putting them across the 120
>>> or 240 volt power wires is somewhat doubtful. I sure would not use one
>>> where I worked to put across the 480 volt 3 phase system that is fused
>>> with 200 amps.
>>
>> I'm pretty timid with anything upstream from a plain outlet.
>
> I've replaced outlets (240V, not the namby pamby USA stuff) without
> turning off the power - other outlets on the same circuit were being
> used in the office and I saw no point in interrupting them.

cool story.

> Just keep your fingers off the metal things and don't short stuff together. Wear goggles and gloves if you want to be a girl about it.
>
>> I had an
>> edison base fuse burst in my hand once. Never seen one come apart before.
>> It was just a 120v lighting circuit, but right off the service panel.
>> There's way more excitement near those things.
>
> Try shorting two phases together with 500A cables. That causes lots of
> smoke, a fire alarm, 3 fire engines, and a visit from the power company.
> Do not ever employ Irish electricians.

In America we have fuses and circuit breakers. Check youtube for a video
about how they work.