[R-390] Meters
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Thu, 8 May 2003 13:45:22 -0400
Barry is almost right:
Put an 11.11... ohm resistor in parallel with the 100 ohm, 100 uA meter.
Put a 7 ohm resistor in series with the meter/11.11 ohm resistor
combination. The composite network will have a resistance of 17 ohms and
the 100 uA meter will read full-scale when 1 mA flows through the 7 ohm
resostor.
73,
Ed N3CMI
"Scott, Barry
(Clyde B)"
<[email protected] To
> Roy Morgan <[email protected]>,
Sent by: [email protected]
r-390-admin@mailm cc
an.qth.net
Subject
RE: [R-390] Meters
05/08/2003 12:16
PM
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
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