Dear Gideon

Hi,

yes

Certainly a Tacho generator will do the job. It is best transducer for RPM measurement

Dear muhammad

can you explain more?!

Techo meter is a generator which when connected with some revolving shaft..it will provide you voltage (0.7v per 1000rpm).caliberated instruments will provide you the rpm reading this voltage

Should I buy it?

how much is it?

Small meters cost almost 20$

while for diesel engine models etc it may be more then 50$.

But sorry to say i have no experience of bying it..i just used it in lab with 3-phase induction motors.

Dear muhammad

thank you so much

Gears.

Esmaeli,

There are numerous ways to measure the rotation speed of a motor.

The advantages of each method critically depend on;

a) your budget

b) the desired accuracy

c) the scale and speed of the motor.

(I'll presume that this is a DC motor)

Note, if you *very* accurately measure the current and voltage across the motor then it is entirely possible that you'll see some harmonic content that is related to the shaft rotation. But I wouldn't do this - far too fiddly, prone to error, and wear in the bushes is not something that should be relied upon.

No, I'd keep it simple. An optical or magnetic pick-up and a simple frequency to voltage chip and you then have an analogue value that is both robust, can be calibrated, and is cheap.

I've used beam-break opto-couplers on shafts, and am presently exploring Avago's magnetic sensors ($7 and 16 bits of absolute rotation sensing!)

But you want rotation speed, not shaft angle.

Well, about 15 years ago, for my PhD I simply glued some bar magnets on to the rim of the disc I wanted the speed of. A reed switch, a few resistors, a 5V rail, and a very basic ADC, all gave me a rotation sensor good from 0 up to 10 revs per second at almost no cost and time penalty.

Make a better job of it, or even better, buy a dedicated sensor, and you'll have something for your purpose.

Whatever that is.

More details would be nice (shaft speed, size, environment, etc.

How about this?

http://www.ebay.com/itm/Professional-Digital-Laser-Photo-Tachometer-Non-Contact-RPM-Tester-Tach-Meter-/141060453750?pt=LH_DefaultDomain_0&hash=item20d7dbb576

It uses the reflected beam from a laser to determine the absence/presence of a blade. Very reliable. Solid state, a sure win. Cheap too!

Dear akash

thanks

Dear james

thanks for your best answer

Dear james

your link is very useful for me.

thanks for that

Dear Omid

thanks alot