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#2220
by
jay343
on 17 Oct, 2017 17:15
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Have you tried monitoring the temperature, humidity, and/or the ambient electromagnetic fields in and around the balance? Maybe one of those will track the noise.
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#2221
by
Rodal
on 17 Oct, 2017 17:39
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Something is causing the pendulum to move in unexpected ways. It has too many degrees of freedom in my opinion and needs to be constrained to the one we are measuring.
The plan is to remove the piano wire and replace it with flexure bearings. I have to be careful that I use flexure bearings that do not exceed by much the current 0.00326 lb-in per degree torsion spring constant but can still support ~25lbs. That means I can use either one E-10 c-flex bearing (0.0036 lb-in per degree, 36.5lbs axial load capacity) or two D-10 bearings (0.0018 lb-in per degree, 22.7 lbs axial load capacity). I will also be replacing the rectangular damping fluid reservoir with something circular.
I ordered the three flexure bearings today, as they are not very expensive, but installing them is going to require a couple of weeks.
Consider measuring air speed inside the enclosure (it can be done wirelessly) and see whether you can correlate it to the noise. Even within the enclosure you have natural thermal convection, because the size of your chamber is such that you are never going to eliminate natural thermal convection (unless you use a vacuum chamber).
Recall the videos of rfmwguy and the natural movement of his device in his garage.
See for example:
http://www.tsi.com/uploadedFiles/_Site_Root/Products/Literature/Spec_Sheets/AirPro%20500_US_5001784_Web.pdfwhich has a
minimum of 3 feet/minute = 0.015 m/s
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#2222
by
Bob012345
on 17 Oct, 2017 17:45
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Could you describe your rig when you are running calibration pulses? Does disconnecting all of the batteries on the rig have any effect on the noise profile during calibration?
For your calibration pulses, are you using a permanent magnet on the torsion arm, and an electromagnet nearby? Would it be possible to physically move the electromagnet after the calibration pulse? A moving permanent magnet can induce currents in a nearby electromagnet, so I was wondering if that might be one of the noise sources. Increasing the size of the air gap after the calibration pulse finishes would help test whether the electromagnet was having any effect on the noise.
Does the noise profile look different if the calibration pulse is stronger/weaker?
With everything unplugged and unpowered, I still get the noise. The calibration pulse is simply a small electromagnet outside of the enclosure. Inside the enclosure attached to the pendulum is a small aluminum arm that extends to 4cm away from the calibration coil. Attached to this arm is a small ferromagnetic screw. I use the electromagnet at a known distance and current to exert a force on the screw. Yes, I still get the noise even if the calibration coil is taken away.
I also performed a test increasing the air-gap. See below. The little spike in the middle in me moving the coil. This was one of the better runs.
A long shot but are you breathing near the test setup during the runs?
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#2223
by
jmossman
on 17 Oct, 2017 18:00
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Something is causing the pendulum to move in unexpected ways. It has too many degrees of freedom in my opinion and needs to be constrained to the one we are measuring.
The plan is to remove the piano wire and replace it with flexure bearings. I have to be careful that I use flexure bearings that do not exceed by much the current 0.00326 lb-in per degree torsion spring constant but can still support ~25lbs. That means I can use either one E-10 c-flex bearing (0.0036 lb-in per degree, 36.5lbs axial load capacity) or two D-10 bearings (0.0018 lb-in per degree, 22.7 lbs axial load capacity). I will also be replacing the rectangular damping fluid reservoir with something circular.
I ordered the three flexure bearings today, as they are not very expensive, but installing them is going to require a couple of weeks.
I do not agree. The noise problem is caused by a noise source, not by the degree of freedom of movement. Just find the noise source, remove it and the experiment is good to go.
Also flexure bearing has its own problems. It will droop and transform mass center shift into thrust-like force.
@Monomorphic,
I think the "noise" you are seeing is because your rig acting like a seismograph.
A quick Google search came up with seismic Rayleigh waves being well within the frequency range of the noise you are observing:
http://www.ucl.ac.uk/EarthSci/people/lidunka/GEOL2014/Geophysics4%20-%20Seismic%20waves/SEISMOLOGY%20.htmRayleigh waves
period is typically ~ 20s, with wavelength of ~100km
I'd recommend reviewing some of Seeshell's (and Dr.Rodal's) earlier posts about building vibration isolation for your stand (i.e. desk) as the next step before attempting a switch to flexure bearings. The larger mass of your desk/enclosure should help with tuning the vibration isolation (if I recall the details correctly). I'd recommend losing the wheels on the desk/enclosure (at least temporarily) if one were to pursue vibration isolation options.
-James
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#2224
by
drjrkuhn
on 17 Oct, 2017 18:01
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Consider measuring air speed inside the enclosure (it can be down wirelessly) and see whether you can correlate it to the noise. Even within the enclosure you have natural thermal convection, because the size of your chamber is such that you are never going to eliminate natural thermal convection (unless you use a vacuum chamber).
I'm chiming in from the microscopy world for the laser displacement measurements. For optical trapping experiments, Steven Block mentioned that he had to replace air in his setup with helium, which has an index of refraction 10x closer to vacuum than air. Helium eliminated a lot of the thermal convection noise.
Columns of air heat up, and that changes the index of refraction significantly enough to modify laser deflection measurements! Think of a heat mirage on a hot day, or hot microwave-powered device in an enclosed space. Now try to perform a displacement measurement through that shifting mirage. In contrast, the n of helium changes much less with temperature than does air.
To quote from a paper:
https://jila.colorado.edu/perkins/sites/default/files/pdf/Perkins%202014%20Angstrom%20Precision%20Optical%20traps.pdfThe final hurdle to measuring 1-bp [base-pair] steps of RNAP [RNA polymerase] was further suppression of low-frequency (<0.3 Hz) noise. This suppression was achieved by replacing the air surrounding the optics with helium to minimize beam pointing fluctuations caused by air currents (1). The tenfold reduction in the difference between the index of refraction of the gas and that of a vacuum led to a more than tenfold reduction in the integrated positional noise at 0.1 Hz. With this improved performance, Abbondanzieri et al. (1) resolved 1-A˚ steps of a trapped bead that stayed in register over approximately eight steps (Figure 5c).
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#2225
by
jay343
on 17 Oct, 2017 18:16
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Rayleigh waves
period is typically ~ 20s, with wavelength of ~100km
I'd recommend reviewing some of Seeshell's (and Dr.Rodal's) earlier posts about building vibration isolation for your stand (i.e. desk) as the next step before attempting a switch to flexure bearings. The larger mass of your desk/enclosure should help with tuning the vibration isolation (if I recall the details correctly). I'd recommend losing the wheels on the desk/enclosure (at least temporarily) if one were to pursue vibration isolation options.
-James
[/quote]
If there is a source of common mode noise like this, another thing you can do is to record it separately, then scale it and subtract it from your data.
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#2226
by
Monomorphic
on 18 Oct, 2017 01:07
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I removed the sorbothane pads from beneath the torsional pendulum supports and that seems to have eliminated most of the noise. We will see if it is repeatable tomorrow, but this looks promising.
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#2227
by
spupeng7
on 18 Oct, 2017 04:57
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Time is gravity?
Almost Kenjee,
gravity is time dilation, to be more specific. Problem is we don't really know how time dilation acts to engender gravitational acceleration, do we... Ideas anyone?
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#2228
by
meberbs
on 18 Oct, 2017 07:19
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Time is gravity?
Almost Kenjee,
gravity is time dilation, to be more specific. Problem is we don't really know how time dilation acts to engender gravitational acceleration, do we... Ideas anyone?
Gravity is more than just time dilation, and time dilation is caused by any acceleration (or just by having a relative velocity) so it doesn't make sense to say that time dilation causes gravity.
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#2229
by
ThatOtherGuy
on 18 Oct, 2017 07:25
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I removed the sorbothane pads from beneath the torsional pendulum supports and that seems to have eliminated most of the noise. We will see if it is repeatable tomorrow, but this looks promising.
Way to go, Jamie !!!
I wonder if, placing some marble "bricks" under the supports may further improve things; as for the whole bench wheels, here's an idea; you may remove them and replace them with fixed supports and then, when needed, use something like
these to move the stand around, this way you'll be able to have a (possibly) more stable bench
HTH
[edit]
placing some marble "bricks" under the supports
I meant using marble slabs (possibly somewhat thick) between the bolt and the table (in place of the sorbothane pads)
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#2230
by
DusanC
on 18 Oct, 2017 07:41
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I removed the sorbothane pads from beneath the torsional pendulum supports and that seems to have eliminated most of the noise. We will see if it is repeatable tomorrow, but this looks promising.
There is always a gap between screw and nut so I propose you reconstruct that support like in attached pic to stop possible oscillations of whole setup around its center of gravity.
You adjust height with lower nut and lock the support position with upper one.
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#2231
by
Eusa
on 18 Oct, 2017 10:02
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In fact, when supporting setup with flexible material you can make use of the upwards acceleration of the surface of the Earth little similarly to the setup with LIGO instruments make use of intential horizontal acceleration for masses with mirrors.
Way up, Jamie!
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#2232
by
flux_capacitor
on 18 Oct, 2017 10:31
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Can someone please explain why the sorbothane pads used by Jamie, which are intended to absorb and diminish vibrations transmitted to the setup, seem to conversely do the opposite? Is there an effect of resonance, relative to their size, thickness, and the size of the setup? Or may it be just a bad junction between bolt and screw as DusanC supposed?
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#2233
by
Ricvil
on 18 Oct, 2017 10:50
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Hi guys
Look at this article, fig 3
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-15-17249The blue and red lines are the probabilty to find a foton at left and right cavity respectly.
Then, if a cavity mode is a huge numbers of fotons acting in collectivity, and the energy density of electromagnetic modes in cavities has a "center of mass", then this system presents a oscilating center of mass?
A fast oscilation of a center of mass can produce a gravitational wave?
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#2234
by
DusanC
on 18 Oct, 2017 11:24
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Can someone please explain why the sorbothane pads used by Jamie, which are intended to absorb and diminish vibrations transmitted to the setup, seem to conversely do the opposite? Is there an effect of resonance, relative to their size, thickness, and the size of the setup? Or may it be just a bad junction between bolt and screw as DusanC supposed?
There's also a gap between screw and hole in Monomorphics supports so his supports are only axially fixed but radially, especially with a point contact between screws head and pads, they're loose so whole frame can have small displacement in horizontal plane.
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#2235
by
Eusa
on 18 Oct, 2017 11:26
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Can someone please explain why the sorbothane pads used by Jamie, which are intended to absorb and diminish vibrations transmitted to the setup, seem to conversely do the opposite? Is there an effect of resonance, relative to their size, thickness, and the size of the setup? Or may it be just a bad junction between bolt and screw as DusanC supposed?
I think there must be a "counter-press" to keep vibrations between standard strength scale. In other cases there are arbitary interferences...
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#2236
by
SeeShells
on 18 Oct, 2017 11:43
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I removed the sorbothane pads from beneath the torsional pendulum supports and that seems to have eliminated most of the noise. We will see if it is repeatable tomorrow, but this looks promising.
Now that's weird, although your setup in the way the screw attaches to the beam support might lead to non-uniform loading on your legs that might cause issues. I'd recommend a simpler fix by using Elevator Screws and get rid of all the other hardware by using two nuts to set height and still use the sorbathane pads.
Shell
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#2237
by
Peter Lauwer
on 18 Oct, 2017 13:27
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I removed the sorbothane pads from beneath the torsional pendulum supports and that seems to have eliminated most of the noise. We will see if it is repeatable tomorrow, but this looks promising.
The flexible pads with the mass of your setup made up a resonance frequency that (almost) matched up the swinging freq of your balance?
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#2238
by
sghill
on 18 Oct, 2017 13:40
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#2239
by
dustinthewind
on 18 Oct, 2017 14:05
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Time is gravity?
Almost Kenjee,
gravity is time dilation, to be more specific. Problem is we don't really know how time dilation acts to engender gravitational acceleration, do we... Ideas anyone?
Gravity is more than just time dilation, and time dilation is caused by any acceleration (or just by having a relative velocity) so it doesn't make sense to say that time dilation causes gravity.
That seems to me to be in question because we don't really know the source of what causes the time gradient. It is really just because of relative velocity (or existing under acceleration) or something more fundamental that causes time to change?
For instance what if the vacuum is made up of positive matter that runs forward in time and negative energy matter that run backwards in time. The negative energy matter appearing in our universe as positive energy matter because it runs backwards in time but then it annihilates with positive energy matter their time cancels out between them and suddenly they annihilate. While separation because of the time aspect allows them to have what appears as positive energy.
Maybe for some reason this negative energy matter in the vacuum is attracted to large masses of positive energy matter. As a result this polarization causes a time gradient in the vacuum and maybe even phase shifts in the vacuums equilibrium with matter causing what appears to be gravity.
Maybe these backward time particles also are responsible for the Wheeler-Feynman effect?
Maybe having a large velocity in the vacuum also polarizes these particles causing Lorentz contraction and the time effects.
One of my own hypothesis I have been toying with for a while.
