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# Measurement of RPM's of Dc Motor

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#### zeshan

##### Junior Member level 2
how can i exactly measure the RPM's of a fast DC motor (15000 RPM)????????are such motors available in Markets?plz guide me

via infrared sensor

thanx.but are not these Expensive????? I M A STUDENT and want toimplement for my project

zeshan said:
how can i exactly measure the RPM's of a fast DC motor (15000 RPM)????????are such motors available in Markets?plz guide me
If only need to measure the RPM take any open optocoupler and slotted disk. So you wiil be able to do that! If you also want to measure angular position you should be ready to spent much of money. Encoders for high speed are very expensive.

how much money? what about the availablity of such motors?????? plz guide

Here is a link for 15000 RPM motor, you can find further details
Raoof

zeshan said:
how much money? what about the availablity of such motors?????? plz guide
Quiet! As I told you if you only need to measure the angular velocity you shouldn't worry about the cost.

u can get these optical sensors free
just find an old Ball mouse thatz it

zeshan said:
thanx.but are not these Expensive????? I M A STUDENT and want toimplement for my project
When you say you need to measure the speed up to 15000 RPM, the circuit or the sensor too shud be fast enough to process and display the same. Thus if you are calculative with the component cost, so will be the results. Cheers.

can optocoupler help us measuring upto 15000 RPM????????? Acurately

Yes, all you need is an opto-coupler, or more accurately an opto switch.

You need access to something rotating on the motor, it could just be a point on the motor shaft but it gets easier if you can use something with a larger diameter. All you have to do is use a reflective opto switch and place it close to the moving part. Make a section of the moving part reflective and part of it non-reflective. The light from the opto switch shines on the part and whether or not it sees a reflection depends on the rotational angle (reflective or non-reflective section is in front of the switch). all you have to do then is count the frequency of the reflections, you get one per revolution so it is easy to measure.

If you can access a disk rotating on the shaft you can do the same thing by passing or blocking light through it and using a slotted opto switch instead.

I would be cautious about using a ball mouse opto system, with typically 100 holes in the wheel and at 15,000 RPM the pulses would be very fast, possibly 25KHz or more so counting might be more difficult.

Brian.

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