| Electronics > Projects, Designs, and Technical Stuff |
| Seismic Sensors |
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| Rerouter:
You can also go all the way to the extreme with a laser tractor beam, essentially a tiny spherical lens is held in place by the photon momentum, and by measuring the deflection of the light you can measure extremely tiny forces. |
| radioactive:
--- Quote from: rhb on January 11, 2019, 11:06:36 pm ---A few comments: Take a look at this thread: https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1531160/#msg1531160 in particular the differential capacitance sensing. The results achieved are quite amazing. --- End quote --- @rhb, thanks for pointing to that thread and the other thoughts. That simple capacitive sensor is pretty amazing. I assume that is just water/air (80/1) in the vials based on the Ames description? I think I might start with this sensor and see if I can get similar results in the garage. @diegogmx, thanks for thoughts on the laser. After watching the appliedscience video, I was thinking that it might be possible to utilize the idea of modulating the power supply + DSP to get some higher resolution measurements. I'll be doing a digikey order soon. I might pick up a diode with the integrated PIN to play around with. @Rerouter --- Quote ---You can also go all the way to the extreme with a laser tractor beam.... --- End quote --- Then profit! |
| Rerouter:
Sorry, the more correct term was Optical Tweezers, Its how they measure extremly small forces |
| rhb:
Spirit levels are filled with alcohol so they won't freeze and break. Hence the name. It's probably worth spending a little extra and getting the UK made vials. The interior finish on the Chinese vials is a bit rough and leads to erratic movement. Not important in a machinist's level, but JBeale found it problematic for a monitoring application. If you happen to live near a volcano or a major fault zone you can do serious science by setting up an orthogonal pair on a bedrock mounting. If you've got a good setup with the vials accurately oriented USGS will be glad to get data from you. I'd talk to USGS before making the permanent mount. They may know from experience that there are some wrinkles to getting good data. Also they'd probably want to do a calibration of your unit before installation. I dropped my membership in the Seismological Society of America some years back so I don't know the current details, but USGS has a sizable network of tiltmeters all over California. It's a good bit of work to calibrate and integrate a new instrument, especially a seismograph installation, into the network so to work with them you'd need to be very professional in your dealings with them. That mostly requires that you read and understand the relevant recent literature. Those papers will also tell you who to contact. I strongly suspect that the same circuit and electrode arrangement with a piece of teflon rod would be equally sensitive in a seismograph application. I'm used to seeing ads in the geophysical journals for microradian tiltmeters for many years and understood how they worked, but I never imagined it was as simple to make one as it is. The commercial units are quite expensive. |
| mark03:
--- Quote from: diegogmx on January 11, 2019, 06:37:31 am ---One interesting method i know modern seismometers use is to have a test mass as an lvdt moving element, and using a control loop and a coil to keep the lvdt output at 0, the seismometer output waveform would be the output of the control loop, they use one of these for each axis, buying one of these would most likely be prohibitively expensive yet it would be an interesting (and probably damn hard) project for summer (unless you are in the north hemisphere) :) --- End quote --- This is known as "force feedback" and is a staple of all modern broadband seismometers, including the amateur FBV instruments mentioned up-thread. It's analogous to negative feedback in electronic amplifiers, yielding a flat response over multiple decades of frequency. Older and simpler designs like the Lehman, and I believe also the Benioff mentioned by @GK, are merely second-order damped pendulums whose bandwidth can only be expanded through post-processing. With force feedback, it is possible to achieve the same (actually, much better) performance at low frequencies, without the heavy seismic mass. |
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