Measuring Displacement With Accelerometer
Measuring Displacement With Accelerometer
(OP)
Background:
I have a "rigid" metal frame attached to a vibration stand. Housed in the "rigid" frame is a plastic tank with hard contact points on the top and two steel bands holding the tank on the bottom. The two bands fasten to the sides of the "rigid" frame and when tightened compress the plastic tank into the top contact points assuring a tight fit.
I'm shaking the tank 3G peak-to-peak at 13Hz.
I am noticing that the fit of the tank is loose when shaking and tight again once I stop. When vibrating the steel bands seem to be flexing controbuting to the looseness condition.
Question:
If I put an accelerometer on the middle point of each band (or whereever I feel I am getting maximum bending) can I use those to measure the displacement of the bands relative to the control accelerometer. My thought is that if the band is rigid and does not bend then they should read the same acceleration as the control. If the bands are bending then the accelerometers should read a higher acceleration than the control and I can calculate the displacement from the delta between them. I'm guessing that the peak accelerations wouldn't be in phase with each other but it shoudln't matter since I only care about the maximum between the two at one cycle.
I would like a little sanity check before I waste time pursuing.
I have a "rigid" metal frame attached to a vibration stand. Housed in the "rigid" frame is a plastic tank with hard contact points on the top and two steel bands holding the tank on the bottom. The two bands fasten to the sides of the "rigid" frame and when tightened compress the plastic tank into the top contact points assuring a tight fit.
I'm shaking the tank 3G peak-to-peak at 13Hz.
I am noticing that the fit of the tank is loose when shaking and tight again once I stop. When vibrating the steel bands seem to be flexing controbuting to the looseness condition.
Question:
If I put an accelerometer on the middle point of each band (or whereever I feel I am getting maximum bending) can I use those to measure the displacement of the bands relative to the control accelerometer. My thought is that if the band is rigid and does not bend then they should read the same acceleration as the control. If the bands are bending then the accelerometers should read a higher acceleration than the control and I can calculate the displacement from the delta between them. I'm guessing that the peak accelerations wouldn't be in phase with each other but it shoudln't matter since I only care about the maximum between the two at one cycle.
I would like a little sanity check before I waste time pursuing.





RE: Measuring Displacement With Accelerometer
What are your accels telling you currently? If they're really loose, then you should already be seeing a resonance when that occurs. If you don't adding another accel probably won't help.
TTFN
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RE: Measuring Displacement With Accelerometer
Just by watching it shake and seeing daylight between the top of the tank and the hard mounting points. I would say it's roughly 5 mm. It's apparent that the design needs to change, however, I would like to quantify the deflection so I can correlate it to an FEA model and prove out the new design in FEA first. My reason to try and quantify it is that the ~5 mm I am seeing may not be all from the bands.
>>>What are your accels telling you currently? If they're really loose, then you should already be seeing a resonance when that occurs. If you don't adding another accel probably won't help.
Up until this point I have not ran with any accelerometers on the points described. I just watch the test earlier today and was trying to think of a way to quantify the amount of bending. I could easily put some accelerometers on the bands but if my general thought process is way off then I'm just wasting time. In this current environment wasting resources to get garbage just doesn't fly.
RE: Measuring Displacement With Accelerometer
RE: Measuring Displacement With Accelerometer
RE: Measuring Displacement With Accelerometer
The accelerometer may help you but while it may provide data it may not provide information.
Cheers
Greg Locock
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RE: Measuring Displacement With Accelerometer
If the bands are separating from the unit, then the unit will be doing something other than what's being driven by the shaker, and that should show up in the response as a resonance, or at least, an anomaly.
In any case, while displacement, as others have mentioned can not be readily detected, decoupling of the bands from the frame/box, or decoupling of the box from the frame, will should show up as resonances.
TTFN
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RE: Measuring Displacement With Accelerometer
Displacement transducers might help, but the timed optical approach is good for this application
Ron
RE: Measuring Displacement With Accelerometer
- Steve
RE: Measuring Displacement With Accelerometer
RE: Measuring Displacement With Accelerometer
(pi=3,14)
RE: Measuring Displacement With Accelerometer
RE: Measuring Displacement With Accelerometer
d=a/(2*pi*f)^2
With a=3g at f=13 Hz:
d=3*9810/(2*3,14*13)^2
d=4,42 mm
RE: Measuring Displacement With Accelerometer
RE: Measuring Displacement With Accelerometer
- Steve
RE: Measuring Displacement With Accelerometer
Moreover, you apparently have no other accel information, so you have no idea what the actual acceleration is on the tank, only what's driving the frame. You could have 10 g or 20 g of acceleration on the tank because of a resonance.
TTFN
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