Post by thread:[ot]: Strain Gauges?

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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

OK, thanks. ----- Original Message ----- From: "Kübek Tony" <spam_OUTtony.kubekTakeThisOuTFLINTAB.COM> To: <.....PICLISTKILLspam@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 ²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²² E-mail: tony.kubekKILLspamflintab.com ²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²² -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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 -- Dr. Chris Kirtley MD PhD Associate Professor HomeCare Technologies for the 21st Century (Whitaker Foundation) NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation Dept. of Biomedical Engineering, Pangborn 105B Catholic University of America 620 Michigan Ave NE Washington, DC 20064 Tel. 202-319-6247, fax 202-319-4287 Email: .....kirtleyKILLspam.....cua.edu http://engineering.cua.edu/biomedical Clinical Gait Analysis: http://guardian.curtin.edu.au/cga Send subscribe/unsubscribe to EraseMElistprocspam_OUTTakeThisOuTinfo.curtin.edu.au -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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}> > 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 ). > > Sidenote: I've seens some 'in-official' ( i.e. secret prototypes ) of a > piezo based > 'loadcell' that could measure both tension and compression, this was > fastened > directly onto any type of beam ( part of a construction, support, > whatever ) > using magnetics. It then somehow had 'testpins' penetrating the surface > of the > beam ( to fixate them ). Now by applying load to this beam ( could be > part > of a bridge or similar ) you measured the compression/tension of that > beam. > Ofcource the accuracy was nowere near normal loadcells but still a neat > little > device ( maybe 3x5x2 cm in total ). > > >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. > > See above. > > >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. > > Could be :) > > >Do this type of thing exist?? > > I would guess yes. > > >As always, thanks in advance. And by the way, you guys are the > >greatest. -;) > > No worries, > > >Rick > > /Tony > > Tony K|bek, Flintab AB > 222222222222222222222222222222222222222222222222222222222222 > E-mail: tony.kubekspam_OUTflintab.com > 222222222222222222222222222222222222222222222222222222222222 > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use @spam@listservKILLspammitvma.mit.edu?body=SET%20PICList%20DIGEST