Re: Understanding the (point of) the Wheatstone Bridge

On Fri, 21 Sep 2007 02:18:05 +0000, Jamie Jackson wrote:

My son and I are working through some circuits from a Forrest M.
Mims / Radio Shack learning lab. We got to a Wheatstone Bridge
circuit, but I'm trying to understand the usefulness of it.

Let's use this diagram, for reference:
http://en.wikipedia.org/wiki/Wheatstone_bridge

If you need to adjust R2 in order to get the value of Rx, how do you
even know what R2 is anymore (since you've adjusted it)? Is R2 some
fancy high-accuracy *graduated* variable resistor that I've never
heard of?

Yes, it's typically a variable resistor with a graduated knob on it.

Or it might be a multi-way switch and a ladder of fixed resistors. Or
several of them (e.g. one switch with 10 1kOhm resistors and one with
10 100Ohm resistors, giving 0-9900 Ohms in 100-Ohm steps).

After seeing the diagram, I'm thinking: Well, if I have to measure my
R2 with my multimeter, I might as well measure Rx while I'm at it,
which blows the point.

Is the point just that they're perfectly balanced, and the point is
not what the actual values are?

You need to know the value of R2.

.

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