January 2013 Gravimeter

If there's an article in Nuts and Volts that you would like to discuss, this is the place!
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upand_at_them
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January 2013 Gravimeter

Post by upand_at_them » Mon Dec 24, 2012 6:43 pm

Could you guys give a little better description of the construction of the sensor in this project? There was no good picture or diagram and the article didn't describe the placement of the wires. The only picture shows only two wires coming from the sensor, but the article says there are four wires.

UhClem
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Re: January 2013 Gravimeter

Post by UhClem » Mon Jan 07, 2013 4:49 pm

It really doesn't matter because it is a horrible sensor and even if it wasn't the system cannot measure at the resolution required.

In spite of what the article claims the variation of gravity at any fixed location will be no more than about 300 microgals. (1 gal = 1 cm/sec/sec). So the plot showing a variation of 1% is measuring something else.

http://principles.ou.edu/grav_ex/acquisition.htm
David Schultz

oldman70
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Re: January 2013 Gravimeter

Post by oldman70 » Tue Jan 08, 2013 12:54 pm

I am having several problems with assembly. The sensor is just one. Anyone interested in a much older article can look up "Detecting Extraterrestrial Gravity" by Shawn Carlson January 2000, Scientific American, Amateur Scientist series. The article gives build info on a sensor that is far more complex and (I guess) would approach lab grade instrumentation.

upand_at_them
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Re: January 2013 Gravimeter

Post by upand_at_them » Thu Jan 31, 2013 7:54 pm

Another thing that bothered me about this project was the use of a DAC just so the author could connect it to his datalogger.

G8RPI
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Re: January 2013 Gravimeter

Post by G8RPI » Thu Sep 26, 2013 9:36 am

Hi,
I would agree that the sensor in this article is pretty useless. There are lots of better ways to do this.
The use of an DAC to feed an analogue data logger on a PC is a common theme with this author. He used it on a Geiger counter design. Analogue to digital to analogue to digital - why bother? Additionally why use an external DAC chip when the PIC used has a hardware PWM module that can do the job with just a resistor and capacitor.

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