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Distance Measurement Sensor

Distance Measurement Sensor

(OP)
Hello All. I am trying to make make a digital measurement tape (Round type which retracts back once pulled out and let go). So, as the tape or thread is pulled out, the distance sensor should be able to detect how much length has been pulled out. I had a hall sensor and a few magnets in mind. But with this I believe I cannot achieve the kind of accuracy that I'm looking for. I am looking for an accuracy of 1 mm and be able to measure from 0.1 cm (or at-least 1 cm)to 3 meters. Can anyone please suggest any sensor ? What type of sensor would be suitable for this kind of application and accuracy ?

RE: Distance Measurement Sensor

Get a shaft encoder like the type used on the back of motors. They're called "incremental encoders".

Here's examples. Encoder Examples

There are a bunch of types for a bunch of applications. You have to figure out what resolution you need. They can run the spectrum on cost from a few dollars to thousands of dollars depending on many variables.

You can likely find some inexpensive ones on ebay as a lot of little bitty 'toy' motors have them.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Distance Measurement Sensor

I would suggest a linear optical encoder. In fact, such a product already exists, although I suspect the price point is way beyond what the OP thinks the cost is going to be. Nevertheless, the link below shows performance up to 200x better than the OPs requirement

http://www.renishaw.com/en/rgh22-incremental-encod...

In fact, Renishaw quotes resolutions down to 2.5 nm for some of their other products:
http://www.renishaw.com/en/linear-incremental-enco...

TTFN (ta ta for now)
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