World's Largest Wheatstone Bridge [Physics]

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From: Bret Cahill on 3 May 2010 22:39

> >>> String a wire back and forth across / along a fault line to measure
> >>> very small displacements in the earth's surface. If the resistance
> >>> and/or tensile strength needs to be higher than a common single alloy
> >>> wire then structural steel cable could be wrapped around a insulated
> >>> wire with a higher resistivity. It could be temperature compensated
> >>> as usual, with another wire of the same length loosely supported
> >>> nearby in another leg of the bridge.
> >>> An abandoned power line may be good to go if it is properly located.
> >>> Good info sometimes comes in small displacements.
> >>> Bret Cahill
> >> Two gps stations on both sides do the same trick
>
> > What's the smallest displacement -- not movement but actual change in
> > _distance_ between two points -- they can measure?
>
> > Bret Cahill
>
> They measure continental drift with them in cm's per year....

The warning might be in microns.

Bret Cahill

From: Michael A. Terrell on 3 May 2010 22:41

"krw(a)att.bizzzzzzzzzzzz" wrote:
>
> On Mon, 03 May 2010 17:29:32 -0700, John Larkin
> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:
>
> >On Mon, 3 May 2010 09:46:39 -0700 (PDT), Bret Cahill
> ><BretCahill(a)peoplepc.com> wrote:
> >
> >>String a wire back and forth across / along a fault line to measure
> >>very small displacements in the earth's surface. If the resistance
> >>and/or tensile strength needs to be higher than a common single alloy
> >>wire then structural steel cable could be wrapped around a insulated
> >>wire with a higher resistivity. It could be temperature compensated
> >>as usual, with another wire of the same length loosely supported
> >>nearby in another leg of the bridge.
> >>
> >>An abandoned power line may be good to go if it is properly located.
> >>
> >>Good info sometimes comes in small displacements.
> >>
> >>
> >>Bret Cahill
> >>
> >
> >Differential GPS and laser rangefinders make a lot more sense.
>
> Sense? You're talking to Cahill, here.

AKA: The world's biggest loaded dummy.

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

From: Bret Cahill on 3 May 2010 22:48

> > String a wire back and forth across / along a fault line to measure
> > very small displacements in the earth's surface. If the resistance
> > and/or tensile strength needs to be higher than a common single alloy
> > wire then structural steel cable could be wrapped around a insulated
> > wire with a higher resistivity. It could be temperature compensated
> > as usual, with another wire of the same length loosely supported
> > nearby in another leg of the bridge.
>
> > An abandoned power line may be good to go if it is properly located.
>
> > Good info sometimes comes in small displacements.
>
> > Bret Cahill
>
> What you are trying to make is a strain gauge. This scheme wont work because
> the gauge has to be attached to the substrate along it's whole length not
> just strung up like a power line. But attaching it to the earth in any
> meaningful way over distance would be next to impossible.

Tie it down every few feet.

> Yes, you can
> compensate for the temperature coefficient of resistance but how do you
> compensate for the change in length due to temperature, coefficient of
> expansion, a very different animal.

If you know the coefficient of expansion then you can correct for it,
either mechanically or later in the calculations.

> I can't see a strain gauge being a
> solution for seismic motions.

Is there any other way to measure very low frequency / very small
displacements?

> The best way is a laser interferometer for small displacements and GPS or
> gross measurements. Only two points need to be attached to the earth with
> these schemes.

What's the accuracy?

Bret Cahill

From: John Larkin on 3 May 2010 22:52

On Mon, 3 May 2010 19:39:58 -0700 (PDT), Bret Cahill
<BretCahill(a)peoplepc.com> wrote:

>> >>> String a wire back and forth across / along a fault line to measure
>> >>> very small displacements in the earth's surface. �If the resistance
>> >>> and/or tensile strength needs to be higher than a common single alloy
>> >>> wire then structural steel cable could be wrapped around a insulated
>> >>> wire with a higher resistivity. �It could be temperature compensated
>> >>> as usual, with another wire of the same length loosely supported
>> >>> nearby in another leg of the bridge.
>> >>> An abandoned power line may be good to go if it is properly located.
>> >>> Good info sometimes comes in small displacements.
>> >>> Bret Cahill
>> >> Two gps stations on both sides do the same trick
>>
>> > What's the smallest displacement -- not movement but actual change in
>> > _distance_ between two points -- they can measure?
>>
>> > Bret Cahill
>>
>> They measure continental drift with them in cm's per year....
>
>The warning might be in microns.
>
>
>Bret Cahill
>
>
>

What warning? Faults creep all the time. Knowing the rate of creep has
zero useful predictive value.

John

From: Bret Cahill on 3 May 2010 22:51

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