What is Digital Multimeter Impedance?

Hi all
I have a Fluke 12 DMM and was wondering what is a impedance of such a
device.
I know that the older analogue Multimeters would be in the range of 10 to
11M ohms.

Cheers,
Kevin.

 

Measure it with a DVM!

John

yes, you can also measure a supply through an xx meg resistor and do
the math.

John

 

Oh thanks.
I should have known that!!

KEvin.

 

Unless your older analog meters had a FET input, the impedance wouldn't have
been anywhere near that high -- more in the ballpark of 1k-100k, actually!

That Fluke Multimeter probably is about 10M, although it's likely to be spec'd
as something like 10M in parallel with, say, 20pF, so by the time you hit
10kHz you'd be down to under 1M.

---Joel

 

doesn't it say in the manual?
Some DMMs are 22 Mohms.

 

Quite high. Have you checked the manufacturer's data ?

Analogue ? You mean moving coil ? Those were usually 50uA movements giving a
20kOhms/V input impedance e.g. 200k when on the 10V range.

Graham

 

I got it 10M using measurement and a little maths!
Thanks I couldn't find the manual.
I actually threw it out as there isn't that muc hto know about the flke 12
there are only 4 buttons on the thing.

Cheers,
Kevin.

 

You mean like specifications?
Smarter to put all your manuals in a file,maybe write the serial number and
date of purchase on them at that time.
Then if you have anything stolen,you have proof of ownership,and if you
choose to sell something,the manual can go along with it.(besides being
able to refer back to the manual if needed.)

 

You should really rethink that and get the manual, that fluke is one of the
special cases that had V-check and because of that its input impedance can
vary a lot, depending on the input voltage. The link to download is
http://assets.fluke.com/manuals/12______umeng0100.pdf
If that doesn't work, on the fluke site select: support then manuals, on the
drop down list:digitalmultimeters, model 10.

 

10/11 Megohm analog meters were built with a dual triode or a pair of
FETs to reduce loading the circuit you were working on. AKA VTVM or
FET-VOM

They had 10 Megohm input impedance on AC, plus a 1 Megohm resistor in
the DC probe to reduce the capacitance of the meter lead to keep it from
interfering with the D.U.T.

I can post a schematic to A.B.S.E if you are not familiar with this
type of meter.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

 

Thanks for that!