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'[ot]: Strain Gauges?'
2000\10\26@015320 by rad0

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Hello Picsters!

I want now to build some sort of strain-gauge-force-measurement-device.

I want this thing to measure both tension and compression, Is this possible
with only one device??

I'm not sure how these things are mounted or how they can be mounted.

However, what I'd like to do is have a magic strain-gauge rod, that I could
mount using some type of rigid clevis on both ends and then wire it up to
measure force in both (two) directions.

Is this possible?  Ideally, it would be great if there existed a fixture
where I
could simply thread a rod and screw it into the device and hook it up to a
pic.

Do this type of thing exist??

As always, thanks in advance.  And by the way, you guys are the
greatest. -;)

Rick

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2000\10\26@115634 by rad0

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OK, thanks.

----- Original Message -----
From: "Kübek Tony" <spam_OUTtony.kubekTakeThisOuTspamFLINTAB.COM>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Thursday, October 26, 2000 2:54 AM
Subject: [ot]: Strain Gauges?


Hi,

>I want now to build some sort of strain-gauge-force-measurement-device.

Ah..finally the topic enters my 'field' :)


>I want this thing to measure both tension and compression, Is this
possible
>with only one device??

Should be possible with some kind on 'blade' (planar beam) construction
( strain gauges on both sides ). Maybe somekind of tourqe loadcell could
be used.

>I'm not sure how these things are mounted or how they can be mounted.

Ok, some minor stuff, building an loadcell ( i.e. a device using
strain gauges ) is not trivial, if accuracy is required, there are both
the topic of temperature compensation ( tricky bit ) and material
selection/design
etc. I would strongly recomend that one buys a ready-made loadcell to
start with
before trying to manufacture one Yourself. It's not impossible ofcource
but there are many pitfalls involved ( glueing among others ).

Further there are different 'groups' of loadcells for different
applications.
You have compression loadcells, single point loadcells, beam loadcells,
tension loadcells, tourqe loadcells etc. I'm am not aware of a loadcell
that can
meassure both tension and compression with some accuracy ( not to say
there doesn't
exists one ).
Normally a loadcell is for one type of use only ( i.e. either
compression, tension or
tourqe for example ).

I will buy a ready made one first, if I can find one and it's not
bizarrly expensive.

However, I was thinking of making one that used a round
gauge, like a washer, that could be placed on both sides
of a piston like rod fixture,

so that it would measure tension one way and compress
the other way.  I thought this piston-like, strain gauge
device could be made out of stainless steel, and have
threads on both sides?

What do you think of this?

Can you get a strain gauge in the form of a washer?

Also,  my requirement is to measure 1-5 pounds
and I wanted to use 1/4" delrin rods threaded.  But of
course I'd like as fine a resolution as possible.
>Is this possible?  Ideally, it would be great if there existed a
fixture
>where I
>could simply thread a rod and screw it into the device and hook it up
to a
>pic.



>Rick


/Tony


Tony Kübek, Flintab AB
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2000\10\26@180458 by Gennette, Bruce

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face
How big can the device be?

If it is a reasonable size (50mm or more long) then there are lots of
different devices available -
Rotary encoder driven by a toothed rod is a simple one.
Another is a pressure transducer reading what happens in a small hydraulic
cylinder.

Strain gauges are fiddly and only show local stress, mechanical
extensometers show grosser, more generalised loading; what exactly are you
looking for?

bye.

> {Original Message removed}

2000\10\26@181307 by Dr. Chris Kirtley

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face
Strain Gauges can be a bit fiddly. I use these force sensotive resistors
from Tekscan (you just make a potential divider with them - easy!):

http://www.tekscan.com/flexiforce.html

They cost about $10 each.

Chris
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Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
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Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
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'[ot]: Strain Gauges?'
2000\11\11@065306 by Robert Rolf
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Load cells that measure tension and compression are available
everywhere.
You're looking for 'S' type load cells (tension & compression).
Do a web search for your terms and you will have lots of sources.

Start with
http://www.omega.com/pdf/
for all the background information you could possibly want.

http://www.tedea-huntleigh.com/
http://www.measurespec.com/catalog/catalog.htm
among hundreds...


We use a small unit (3"x3"x.5") to measure muscle forces in both
directions. It's basically plug in to preamp/digital display and use.
About a $1000C for turnkey. The load cell was about $150 if memory
serves, and one can build a strain guage preamp with any good
instumentation op amp. Many years ago we used the CAZ amp by
Intersil (are they still around?). Comutating Auto Zero OA made for
an idiot proof design.

R

K|bek Tony wrote:
{Quote hidden}

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