micro force sensor or transducer

On 3 Jan 2007 10:00:08 -0800, " snipped-for-privacy@gmail.com" proclaimed to the world:

What is that in grams?

If you're being picky, it's meaningless. One Newton of force will accelerate one gram of mass at 1000 meters/second. Since the acceleration due to gravity at the earth's surface is about 9.8m/s, you can invent a 'gram force' and define it as the force exerted by a gram of mass at the earth's surface -- but why not use the accepted unit?

Tim Wescott wrote in news:pO-dnc- gUqv6tQDYnZ2dnUVZ snipped-for-privacy@web-ster.com:

If you're being super picky, that would be 9.8 m/s/s!

" snipped-for-privacy@gmail.com" wrote in news: snipped-for-privacy@a3g2000cwd.googlegroups.com:

Back in the day, I made a transducer at the nanoNewton scale to measure force from one cardiac fiber at a time. The design theory (which I certainly can't claim credit for) was to butt the square ends of two optic fibers together, loop the muscle fiber around the free end of one fiber in a u-shaped using pulled capillary tubes, and measuring the light that passed from one fiber to the next while the fiber twitched. Different diameter optic fibers would provide different moduli.

The smallest off-the-shelf strain gauge I can remember is the Akers AE801, but I can't find hide nor hair of Akers online. I don't know if they still exist

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If you're being picky, it's 1000 meters/second/second. :-)

Because I don't go to the deli and buy a 5 Newtons of cheese. The attendant measures out kilos by a process called "weighing".

Jerry

Oy! I've been a jerk (m/s^3).

Hopefully the scale is placarded as to the need for recalibration if it's used on another planet.

Older scales, even cheap ones, often used a weight-balance principal, which (barring issues of friction &c) would have measured mass in any uniformly accelerated frame of reference.

I think all the new ones use force sensors, and depend on the acceleration of gravity, which as any schoolchild knows is one slug per pound.

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Ugh! Mighty big slugs! I've seen shrimp for sale at 3 per pound, and even they were huge.

I'm partial to poundals, myself.

Jerry

I am glad you having fun at this post, guys this is really important and if any one has any ideas I will be more than glad to share it with him . the application I am working at right now is a simple nano-indentation machine , the indenter applies micro force on the sample that I am testing . I am applying this force using a nano linear stage, unfortunately the input parameter for the linear stage is displacement but the stage is connected to a controller so if I can measure the load applied when the linear stage moves I will be able to do some kind of closed loop feed back system so I can control the movement of the linear stage. so basically what I am saying the sensor or the transducer should be able to be connected to moving structure , thanks again and appreciate your help .

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On Thu, 04 Jan 2007 12:11:44 -0500, Jerry Avins proclaimed to the world:

Jerry is correct here. I needed a familiar scale so I could get an idea of how much force that was. I understand the difference between force and weight.

Having an idea of scale now (I figured it was small), I can visualize ways of building a sensor. I don't know how unusual it is to be measuring something of this scale.

If nothing off the shelf is available, you can often make something that will work by making something sensitive enough to produce a motion large enough so that the motion can be measured with something off the shelf. For instance I could use some taut band stock used in meter movements, pulled tight in a frame and attach a balanced arm. I then could measure the movement of the arm when a very small force is applied using a capacitance prox sensor. Another approach would be using a strain gauge glued to some sort of taut band configuration.

But I don't have enough information to know if this is feasible to the OP, what his requirements are, etc. I'm just doing mental exercise. I could have looked up the conversion, I most likely have a calculator with that conversion on the computer I am sitting at, I was being lazy in some ways. I just thought the OP might know it off the top of his head.

On Thu, 04 Jan 2007 09:26:40 -0800, Tim Wescott proclaimed to the world:

That is cute. Let's see, what is s^4 called? Yank?

I hope you don't feel that the fun is at your expense. I also hope you know that if we had anything of value to contribute, we would have done that already. There must be devices that can measure 100 micrograms, but I don't know what they are.

Some of the readers here are good inventors. What are your size constraints?

Jerry

" snipped-for-privacy@gmail.com" wrote in news: snipped-for-privacy@42g2000cwt.googlegroups.com:

I've done my best by pointing you to Akers and suggesting a construction if you need to make one. That's usenet for you. The chaff's OK, so long as the wheat is someplace.

snipped-for-privacy@gmail.com wrote: (top posting fixed)

We _are_ having fun with this, but as Jerry mentioned we're not really answering your question because we're stumped.

You're probably stuck with building your own, more's the pity. The only two ways that I can think of, off hand, to build a force sensor is to (a) take something with a know spring constant and measure its deflection, or (b) take something that generates a known force from a known input, servo its deflection to zero, and measure the input.

If your linear stage is friction free you may be able to use the latter method by monitoring its drive when you're just holding it up vs. when you're pushing down.

On Fri, 05 Jan 2007 20:13:39 -0800, Tim Wescott proclaimed to the world:

From what he added, you can eliminate A being ok, which was what I suggested without know the requirements. If this is nanoscale, then the deflection necessary to measure force will be too great for the process. A tiny strain gauge element attached to the device he is using might work. I would just have to know more or see the application to offer anything feasible.

Five or ten years ago "Scientific American" mag. in the "Amateur Scientist" section had a project on measuring the "heartbeat" (or whatever) rate of a flea. The flea was glued to the end of a small "beam" and a strain gage on the beam measured the stick deflections caused by the heartbeats. A small op-amp cct. was also required.

Could someone lookup the issue to help the OP ? . . . .

Feb 1966 page 120 has a cct for the electrocardiogram of a flea. Maybe it is the one?

Yikes! 40 years ago!