Re: Understanding the (point of) the Wheatstone Bridge


"Jamie Jackson" <mySpamB8@xxxxxxxxx> wrote in message
news:1190341085.272074.293050@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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?

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?

Thanks,
Jamie


Hey Jamie,

Well, so far as usefulness of this circuit is concerned, I used to work on
high-speed printers (mainframe environment like banks and oil companies)
that used the Wheatstone Bridge (they called the actual 'box' that housed
the circuit an H-switch) to drive the servo motor that moved the paper at
incredible speed and stop on an instantaneous command. The servo was so
strong it would literally rip your arm off if you happened to be holding the
shaft in your hand when it took off. You couldn't let go fast enough... I
know it has applications in testing unknown components, but that was what
that company used it for. For unknown components, a built in readout can be
used to tell you what is plugged into it, without running the readout
current through the device under test. Can make a useful piece of test
equipment...

All I can think of.

Dave


.

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