Weight of Sphere Covered in Piezo Force Sensors
Weight of Sphere Covered in Piezo Force Sensors
(OP)
Hi all - new here and new to piezoelectric force sensing technology
I need to measure the weight of a sphere dropped onto a flat plane from a height of 1 foot.
(Im sure there is an easier way to do this - but please entertain my hypothesis)
I want to cover the sphere in small circular piezoelectric force sensors so that ~99% of the surface area is covered. I will then drop the sphere and measure the resulting dynamic forces. After the initial impact force (and any forces incurred as the sphere rolls on the plane), could I effectively measure the weight of the sphere by measuring the final semi-static force of the sphere resting on the plane after it comes to a complete stop?
Sphere weight is anywhere between 50lbs and 250lbs
I need to measure the weight of a sphere dropped onto a flat plane from a height of 1 foot.
(Im sure there is an easier way to do this - but please entertain my hypothesis)
I want to cover the sphere in small circular piezoelectric force sensors so that ~99% of the surface area is covered. I will then drop the sphere and measure the resulting dynamic forces. After the initial impact force (and any forces incurred as the sphere rolls on the plane), could I effectively measure the weight of the sphere by measuring the final semi-static force of the sphere resting on the plane after it comes to a complete stop?
Sphere weight is anywhere between 50lbs and 250lbs





RE: Weight of Sphere Covered in Piezo Force Sensors
RE: Weight of Sphere Covered in Piezo Force Sensors
Cheers
Greg Locock
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RE: Weight of Sphere Covered in Piezo Force Sensors
I recall calibrating a piezo pressure sensor using a jury-rigged step input (3-way valve manually toggled between a pressure source and atmosphere). Worked well with some extrapolation of the results.
je suis charlie
RE: Weight of Sphere Covered in Piezo Force Sensors
Initial weight of the sphere must be weighed 'dry". Dropping it in water will not give you weight, but only bouyancy (amount of water displaced by whatever part of the ball is below the water level.)
RE: Weight of Sphere Covered in Piezo Force Sensors
TTFN

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RE: Weight of Sphere Covered in Piezo Force Sensors
The transducers would measure impulse force and impulse time. If you know the drop height, you can calculate velocity at impact. Calculate the unknown mass.
F x t = m x v
Ted
RE: Weight of Sphere Covered in Piezo Force Sensors
Or as others say, what does the weight (mass?) have to do with the drop as such that you can't just measure it on conventials scales of some kind? Before & after drop if something in the process may cause a change.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Weight of Sphere Covered in Piezo Force Sensors
RE: Weight of Sphere Covered in Piezo Force Sensors
another day in paradise, or is paradise one day closer ?
RE: Weight of Sphere Covered in Piezo Force Sensors
The sphere must be the measurement device. I do not know what orientation it is dropped at. I do not know exactly what height it will fall from.
So, will the final force exerted on whatever sensors the sphere stops on be detectable such that I can isolate the electrical charge produced at that point (isolate it from previous noise produced by the sphere while in motion) and convert the signal into weight.
My apologies in advance - trying to be as clear as possible. This is not at all my area of expertise.
RE: Weight of Sphere Covered in Piezo Force Sensors
b> as already mentioned, piezo sensors don't do DC very well, which is what you are essentially asking for
I will refrain from any further input, as it's clear you don't seem to be reading the posts anyway.
TTFN

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RE: Weight of Sphere Covered in Piezo Force Sensors
WHY ONLY DYNAMIC FORCE CAN BE MEASURED WITH PIEZOELECTRIC FORCE SENSORS
The quartz crystals of a piezoelectric force sensor generate an electrostatic charge only when force is applied to or removed from them. However, even though the electrical insulation resistance is quite large, the electrostatic charge will eventually leak to zero through the lowest resistance path. In effect, if you apply a static force to a piezoelectric force sensor, the electrostatic charge output initially generated will eventually leak back to zero.
The rate at which the charge leaks back to zero is dependent on the lowest insulation resistance path in the sensor, cable and the electrical resistance/capacitance of the amplifier used.
In a charge mode force sensor, the leakage rate is usually fixed by values of capacitance and resistance in the low noise cable and external charge or source follower amplifier used.
In a force sensor with built-in ICP electronics, the resistance and capacitance of the built-in ICP electronics normally determines the leakage rate.
When a rapid dynamic force is applied to a piezoelectric force sensor, the electrostatic charge is generated quickly and, with an adequate discharge time constant, does not leak back to zero. However, there is a point at which a slow speed dynamic force becomes quasi-static and the leakage is faster than the rate of the changing force. Where is the point at which the force is too slow for the piezoelectric force sensor to make the measurement? See the next section on Discharge Time Constant for the answer.
Taken from https://www.pcb.com/TechSupport/Tech_Force.aspx
Rather crucially it looks as though with a built in ICP amp you may be able to get a reasonably accurate weight reading for minutes after it comes to rest.
Cheers
Greg Locock
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RE: Weight of Sphere Covered in Piezo Force Sensors
I assume you are not going to actually do this - it sounds more like a theoretical problem?
je suis charlie
RE: Weight of Sphere Covered in Piezo Force Sensors
RE: Weight of Sphere Covered in Piezo Force Sensors
Probably there are other types of transducer that would be much suited to this application, for example fibre optic force gages, but given that the OP seems to be keeping all details close to his chest there isn't much we can do.
Cheers
Greg Locock
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RE: Weight of Sphere Covered in Piezo Force Sensors
And why not attach the force sensors to the flat plate rather than the sphere?
RE: Weight of Sphere Covered in Piezo Force Sensors
As the sphere shall touch the plane in a singularity = a point, the only one who could know its weight is the plane. But then, in order to get a message, you'd need to 3-foot it with a load cell for each foot. A piezo is perhaps not the remedy of choice here (see Gregs post), so why stick to it at all?
If the sphere shall truly roll off from impact a bit, and your accuracy & repeatability requirements allow it, why not use a sort of soft cover which let the sphere sort of sink in depending on weight. This would come out to a height measurement.
Regards
R.
RE: Weight of Sphere Covered in Piezo Force Sensors
weight is weight, a basic property of mass. it weighs the same whether you drop it from a height, or carefully place it on the surface ?? why will the weight change ???
another day in paradise, or is paradise one day closer ?
RE: Weight of Sphere Covered in Piezo Force Sensors
Is this for school? Student postings are not allowed.
TTFN

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RE: Weight of Sphere Covered in Piezo Force Sensors
If you can suspend the ball above the surface then just weigh it in the rig used to suspend it.
RE: Weight of Sphere Covered in Piezo Force Sensors
RE: Weight of Sphere Covered in Piezo Force Sensors
another day in paradise, or is paradise one day closer ?
RE: Weight of Sphere Covered in Piezo Force Sensors
je suis charlie