Hi to all I have to use a device which can sense the position of a gear. for that required to measure number of rotation(rotation counter) and angula position at different time.The gear is attached with a rack so it is not continuous rotation type, it have to rotate in both clockwise an anticlockwise direction. Due to some problem i can not use rotar potentiometer. So please, can anybody suggest me a suitable instrument rather tha potentiometer.
A rotary encoder may work, but if it's a space constraint you're fighting with you won't save anything over a pot.
If the gear doesn't go through a full rotation an RVDT can be very precise for its size, but the readout electronics are a bit involved. Note that if you do web searches on this you want to search on "LVDT" as well -- "LVDT" pops up on web searches much more often than "RVDT" does, and an RVDT is just an LVDT that works over an arc instead of a line.
A resolver has the precision advantages of an RVDT with the same caviats about readout electronics.
If it's a ferrous gear (i.e. if a magnet will stick to it) you can get hall effect encoders that work on gear teeth -- check Allegro microsystems and possibly Agilent semiconductors for details. This will basically be a crappy rotary encoder, but it won't increase your size much.
Let us know more about your application, and we may be able to help you more.
-- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
One of the disadvantages of using a shaft encoder is that the system will 'forget' where it was when it is powered down and will need to go through a reference cyle on power up to establish its home position.
You haven't said what the problem is that prevents you using a multi-turn servo pot, but if the linear displacement of the rack is small enough you could use one of these to give you an absolute position.
Note that the URL may need to be unfolded.
-- John B
Is there some reason you can't just measure the linear displacement of the rack?
Mark Walsh
I had much the same question. Is there any reason that you cannot measure the linear displacement instead? That takes us back to LVDT's linear encoders, inductive sensors (such as Gill's) and maybe even twine on a bobbin. Tht latter might even work for the rotary if it's accurate enough and you can fit a takeup reel on.
Robert
-- Posted via a free Usenet account from http://www.teranews.com
You can buy "string pots" that work like your twine on a bobbin, only they're way more expensive and way more reliable.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
AS5040 Electronic Rotary Encoder...from Austrian Microsystems.
You will need to use a microcontroller or something.
Here's some who has the complete products
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