DVM Meter sensitivity per volt

[PrescottDan]

When working with Video circuits, they say not to use a DVM or Analog meter that is less than 5000 ohms per volt. But to use a Meter that is 20,000 ohms per volt

I don't understand why?

What circuits want you to use a Meter that is 5000 ohms per volt?, and what circuits want you to use a meter that is 20,000 ohms per volt?

 

[KlausST]

Hi,

This is theinput resistanceof the dvm. With a higher ohms per volt rate the resistanceis higher. The current islower.
With a high rate the dvm is a negligible load to the test point and the dvm reading is more precise.

Hope this helps
Klaus

 

[chuckey]

Most DVMs have a constant input impedance of 10 M ohms on their switched ranges with a higher value for the "plug in" different high voltage ranges.
Analogue meters are basically a current meter with resistors in series to convert them to a volt meter. A good meter might use a 50 micro amp meter giving 20,000 ohms per volt. An old fashioned meter might use a 1mA meter giving 1000 ohms per volt.
If you have a voltage divider of say two 100K resistors across a 5 V supply, their centre point should be 2.5V. Using the 1000 oms per volt meter on its 5V range you would read about 5000/100,000 X 5V = .25 V, using the 20,000 ohms per volt meter on its 5V range, you would get 2.37V, with the DVM you would get2.5V.
Frank

 

[PrescottDan]

Well what I have read it is best to measure AC voltages and AC current using a Vacuum Tube Volt meter, Ballantine Model 300 because the sensitivity of the meter.

I'm not sure why

 

[chuckey]

In my above example if you replace the 5 V DC with 5V AC, the sums remain the same, your VVTM might be only 1 M input impedance.
Frank