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World's Largest Wheatstone Bridge

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Mounting a conventional strain gage just at the ends would give you the same output assuming you had the dexterity to glue just the ends. dl/l should be const. over the entire area of the strain gage site.

Correcting for thermal expansion would require temperature data over the entire length.

Adding a +/- nanometer error to a +/- meter error just gives you a +/- meter error.

GPS wouldn't be useful for the actual data.

They claim laser interferometry won't work over long distances, i.e.,

50 km, but they are probably thinking of measuring an entire unknown distance when all that is really necessary is a _change_ in distance.

Maybe use several different meters at different wavelengths so that you don't skip a wave.

Bret Cahill

Reply to
Bret Cahill
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Only in your (extremely small) mind.

Reply to
tm

I can predict that pretty good with strain sensors.

What we need to do is predict this somehow:

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Reply to
Bret Cahill

No, you can't. You won't get a 10 millisecond warning as to when the pencil will break. Now imagine only being able to place a few surface sensors on one face of literally millions of cubic miles of complex, fractured, stressed, moving subsurface stuff. It's like predicting the weather, but much worse: hopeless.

Move to Mississippi.

John

Reply to
John Larkin

Depends on how fast you load the pencil. If you load it over several months or years I'll get at least some warning that it is being loaded.

The linearity / non linearity allows for even better predictions.

It's not really on one face. It's several miles above from what may be a thousands of faces.

No one said it was a easy problem, just that there might be some additional information to exploit.

Distance metrology needs to get the error down to a few microns over

100 km. Apparently laser interferometry is just for short distances, even turbulence will mess up the measurement.

The strain sensor might not work for the simple reason the strains would be so low.

What is the best resolution possible with a bridge?

Another solution might be the World's Largest Seismometer, a proof mass of hundreds of tons.

There might be some hope in averages here.

Geologists seem to be able to make really low confidence predictions. For example the risk of a 7.5+ earthquake over the next month or so is about 5X what it was on average over the past century.

The question is will everything quiet down for awhile after the next

6.0 or will the next 3.0 set thinks up for an 8.5?

High humidity = high entropy

On the other hand low entropy can get you killed.

Bret Cahill

Reply to
Bret Cahill

Absolutely. You can probably estimate the average time between earthquakes. Numbers like 300 +-250 years.

John

Reply to
John Larkin

r

You'll be trying a little harder after a few hours trapped under some rubble.

Here's an effort to circumvent massive machined commercial seismometers with smarter electronics:

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Some waves travel much faster than the 2 mps Raleigh waves that do all the damage. 30 seconds isn't enough time to fix a lunch but it's better than nothing.

Bret Cahill

Reply to
Bret Cahill

No, it is not, and seismometers have been mechanically trivial to build for many decades.

--
Jim Pennino

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jimp

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