Help with dc mototr rpm

Hello all,..

I want to calculate the rpm of a dc motor by using a shaft encoder the motor gives 400 rpm so how can i get the rpm by using that shaft encoder (Note that the rotating wheel is 45 count per revolution).

I only want to know what equations are needed to use it with a microcontroller so i can get the rpm of the motor to make a speed control.

Thanks in advance.

The encoder will give 45 pulses in 1 rev of the motor, at 400 rpm there will be 400 x 45 pulses in 1 minute.
So if you are measuring the frequency (counts per second), you will get 400 x 45 / 60 counts per second.
That is 300 counts per second.

JimB

Thanks JimB for your reply, sorry but also i need to get the angular speed (w) of the motor can i ??

Thanks.

OK, I will state it another way.

When the motor is turning at 400rpm, you will have a frequency of 300hz from the encoder disc.

The speed in RPM = frequency x 1.333
The speed in radians/minute = frequency x 8.377

JimB

Thanks JimB but can you plZ tell me from where you get this numbers (1.333 and 8.377) used in the above equations ??

Thanks.

As I said before:

The encoder will give 45 pulses in 1 rev of the motor, at 400 rpm there will be 400 x 45 pulses in 1 minute.
So if you are measuring the frequency (counts per second), you will get 400 x 45 / 60 counts per second.
That is 300 counts per second.

So, each pulse per second is equal to 400/300 rpm 400/300 = 1.333 rpm.

If you want the angular speed, I assume in radians, and there are 2 x pi radians in a circle, the 1 pulse per second is equivalvent to 2 x 3.142 x 1.333 radians per minute.
(note error in my original post, I wrote radians per second, should be radians per minute. I will correct it).

JimB

Thanks JimB