[TowerTalk] Cross needle meters

[Patrick Greenlee]

Often, meters is meters. D'Arsonval meters are typically used in circuits 
for measuring volts or amps. the same meter can do either or both depending 
on the circuit it is used with. While the meter movement itself might 
require 50. 100 or whatever micro amps for FSD ( full scale deflection) the 
other circuit elements determine its function.

To read currents much larger than the FSD current  you place a shunt 
resistance in parallel with the meter so the meter reads a fraction of the 
total current.

To read voltages higher than that required to achieve FSD you have to 
either: 1. place a resistance in series with the meter so the added 
resistance reduces the meter current to what is required for FSD when the 
voltage of interest for max voltage indicated is applied or 2. use a voltage 
divider circuit with the meter in parallel with one of the resistances in 
the divider chain.

Most "good" (analog) amp meters are as described above.  El Cheapo amp 
meters ala auto parts store variety are often of a different design.

You don't have to have crossed needles to have a two needle meter. You can 
get meters with two needles pivoted from the same point. Typically these 
have needles of different colors to tell them apart.

Patrick AF5CK

-----Original Message----- 
From: Andrew J. Buckler (BBMSC)
Sent: Sunday, February 03, 2013 8:56 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Cross needle meters

Anyone know where I can get cross needle meters, with one volts and the 
other amps? For use inb a linear amp power supply, not a SWR meter (there 
seem to be forward/reflected meters, but can't find V/A).

Thank you,
Andy, K2OP
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Andrew J. Buckler, Principal
BBMSC
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