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'Measuring absolute deflection'
2008\11\25@042040 by Alan B. Pearce

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>One possibility is to use piezoelectric film.  Is piezo
>film good only for measuring change of deflection rather
>than absolute deflection ?

Um, most probably, considering how piezo action works.

>Is there any sensing technology that would measure absolute
>deflection given that I am constrained to a "tape-like"
>sensor that is 20 inches long ?

light interferometry? Could probably be done using an LED, and mix the
reflected light with a reference beam from the same light source, and
measure the movement from the resultant moiré pattern movement. Requires a
reference position that you can use to measure from when the system is
powered up.

2008\11\25@042609 by apptech

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flavicon
face
>I want to measure the absolute deflection of a piece of tape 20 inches
> long.
> One possibility is to use piezoelectric film.  Is piezo film good only
> for measuring change
> of deflection rather than absolute deflection ?
> Is there any sensing technology that would measure absolute deflection
> given that I am constrained to a "tape-like" sensor that is 20 inches
> long ?

Bimorph sensor maybe.
I can't fully understand from the description what you are attempting to
achieve.


  R

2008\11\26@101126 by Martin

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flavicon
face
apptech wrote:
>> I want to measure the absolute deflection of a piece of tape 20 inches
>> long.
>> One possibility is to use piezoelectric film.  Is piezo film good only
>> for measuring change
>> of deflection rather than absolute deflection ?
>> Is there any sensing technology that would measure absolute deflection
>> given that I am constrained to a "tape-like" sensor that is 20 inches
>> long ?
>
> Bimorph sensor maybe.
> I can't fully understand from the description what you are attempting to
> achieve.
>
>
>    R
>

If the maximum point of deflection is fixed at the center and the type
of deflection is known (i.e. catenary versus single pressure point) he
could potentially glance an IR laser at an angle of incidence (ThetaI)
and measure the angle of reflection with a linear array of detectors on
the opposite end of the tape. Or put the laser on an arm giving a
variable ThetaI and use a fixed ThetaR detector.

Other ideas:
vision, sonar, radar, strain gauge, cheap labor & micrometer

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