[R-390] Meters

[Scott, Barry (Clyde B)]

That's what I was thinking.

Assume a 0.1mA meter (100uA) with internal resistance of 100 ohms.  The
parallel resistor should be 1/10 the internal resistance so put a 10-ohm
across it.  The new "internal" resistance will now be 0.11 ohms.  Put a
16.78-ohm resistor in series and it seems this would be an equivalent meter.

Is this wrong?

Barry(III) - N4BUQ


At 09:50 AM 5/8/03 -0500, you wrote:
>Okay, we can figure out the internal resistance.
>
>Now, assume I find a 1ma fs meter that has an internal resistance different
>from what I need.  Is it possible with a combination of series and parallel
>resistors to achieve the 17-ohm (or whatever it needs to be) resistance to
>make it swing full-scale and appear to have 17-ohms in the circuit?


Yes but it won't be full scale one milliamp any more.

If you find a higher sensitivity meter (say 100 uA) movement with higher 
resistance you may be able to make a resistive network to make it behave 
properly (one ma and 17 ohms)

Roy