DVM measuring volts and amps...

[Anthony William Sloman]

On Tuesday, April 25, 2023 at 2:29:50 AM UTC+10, Lasse Langwadt Christensen wrote:

mandag den 24. april 2023 kl. 06.55.37 UTC+2 skrev Anthony William Sloman:
On Monday, April 24, 2023 at 2:22:39 AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 23. april 2023 kl. 18.08.01 UTC+2 skrev Anthony William Sloman:
On Monday, April 24, 2023 at 1:19:18 AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 23. april 2023 kl. 17.04.35 UTC+2 skrev Anthony William Sloman:
On Monday, April 24, 2023 at 12:46:08 AM UTC+10, John Larkin wrote:
On Sun, 23 Apr 2023 03:14:11 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Sunday, April 23, 2023 at 2:14:58?AM UTC-4, Anthony William Sloman wrote:
On Sunday, April 23, 2023 at 4:21:36?AM UTC+10, John Larkin wrote:
I wonder if this works:

https://www.dropbox.com/s/dz1k4d46fwxj8b5/DVM_E_I.jpg?raw=1

the idea being to just ask the DVM to measure the voltage or the
current. The DVM would be a benchtop, probably a Keithley 2100 or
something. The issue is whether the current path is always low
resistance.

Has anyone done this?
There\'s no end of optimistic idiots.

https://en.wikipedia.org/wiki/Four-terminal_sensing

does go into the right way of doing this. It\'s called a Kelvin connection.

I\'m sure JL knows what a Kelvin connection is.

I assume the folks at Fluke and Keithley do too.

Some DVMs have extra terminals on their front panels to make it easy for people who know what they are doing to exploit the technique.

for current and voltage??
Can\'t remember the details, but if memory serves it was it would have been fours sets of banana plug sockets to which you could also clamp spade terminals. You\'d clamp the shunt resistor between the current terminals, clamp a pair of flat metal links up to the voltage terminals, and feed the current to be measured into the lower (current) pair of banana plug sockets, using cables terminated with banana plugs . Nothing all that exciting, but handy.

makes no sense

Didn\'t stop the meter being produced in large enough volume for one of my employers to buy one. It did come off a production line.

but what would be the point?

Quite possibly just to let purchasers who knew about Kelvin connections make a fuss about the technique in front of their less sophisticated colleagues.

I had a least one boss whose sales technique did depend on making the people he was selling to happy to buy the gear, rather than concentrating on making the gear easier to use for the people who ended up using it.

--
Bill Sloman, Sydney