# How to mesure very small change in distance?

1. Aug 17, 2007

### memeplus

if a object changed position by a very small distance, how to mesure it?

2. Aug 17, 2007

### ZapperZ

Staff Emeritus
Define "small". 0.1 cm may be small to you, but in terms of optical measurement, thats the size of our galaxy. Or the earth may be large to you, but in terms of galactic scale, it is minuscule.

Zz.

3. Aug 17, 2007

### memeplus

i mean around 10mm, what are some of the methods, such as electrical or optical experiments or any other method that can measure it, excluding using the dial calibrator?

Last edited: Aug 17, 2007
4. Aug 17, 2007

### DaveC426913

Can you be a little more specific? What kind of objects? What moves them?

Are you a meter maid for Matchbox cars? You could use a tiny piece of chalk and a set of calipers.

5. Aug 17, 2007

### memeplus

let's say the end of a thin beam moved several millimeters under pressure, how to measure that? and generally what are some of the methods to measure very small displacement?

6. Aug 17, 2007

### ZapperZ

Staff Emeritus
10 mm is LARGE. A micrometer caliper would measure something like that easily. You also didn't mention what kind of accuracy you want to measure such things.

Zz.

7. Aug 17, 2007

### memeplus

sorry for all the confusion, it should be mesured without a caliper, that is, by indirect methods.0.1mm accuracy would be ok.

8. Aug 17, 2007

### ZapperZ

Staff Emeritus
You can already see why, if you are vague and give a rather incomplete description of the task in the very beginning, you'll get responses like this and could possibly even annoy well-intentioned people who are trying to help. It is why we always ask for the most complete description of the problem.

As of now, I think I've lost interest in this one, so I'll let others take over.

Zz.

9. Aug 17, 2007

### JeffKoch

What exactly do you want to measure, how accurately do you want to measure it, what are the constraints on what you can use to measure it.

10. Aug 17, 2007

### mgb_phys

Sounds like this is a small scale beam bending experiment.
The best device is probably a laser projected onto the end of the beam which is reflected into a 1d CCD, as the beam bends to position of the spot along the CCD changes. This can be measured very accurately.
I can't rememebr the name of the company that makes them - someone here might be able to help.

Alternately a phase type laser distance meter 'Leica Disto' would give you probably 1mm accuracy.

11. Aug 17, 2007

### rcgldr

Depending on the range required, laser devices can measure sub micron distances. A web search for laser measurment will produce quite a few hits.

12. Aug 17, 2007

### Staff: Mentor

13. Aug 17, 2007

### mgb_phys

We used a HP laser interferometer for our astronomical interferometer, it could track the telescope separation to 1/512 wavelength at distances of 100m - but I suspect it is out of our friends price range!

The devices I was thinking of are these, http://www.me-us.com/laser-sensor/
(no recomendation for this company - first thing google turned up)
It uses a laser at an angle which is reflected back onto a 1d CCD, the distance along the CCD is easy to measure with high resolution which gives a very fine measurement of the distance. Great for close range measurements of reasonably reflective surfaces.

14. Aug 17, 2007

### Staff: Mentor

Hey, cool devices, mgb_phys. Thanks for the link. That's probably just what the OP is looking for. And yeah, I forgot about the price tag of the HP instruments. Even the cheapest one that I think I ever saw was still several \$k.

15. Aug 17, 2007

### mgb_phys

If the OP's beam is bending through a significant angle he might have to put in a correction for the tilt of the mirror but generally these are great for short range non-contact measurements on eg. machine tools.

Lower resolution than inteferometers but much much cheaper.