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I have two main question about the subject of "Quadrature encoder" of DC motors. I provide the following link of a DC motor with integrated encoder: https://www.aliexpress.com/item/1005005947866498.html in the encoder specifications it says: "Basic pulse number : 11PPR" and yet just bellow, it says: "Number of magnetic ring trigger poles: 22 poles (11 pairs of poles)". As far as I understood, the 11 PPR, is the number of pulses per revolution. but what about the second statement, the 22 poles ?

the datasheet of the motor gives RPM=9968 (with no ration) which is approximately 1043 rad/s

what made me to ask this question, is that I have used an arduino mega to measure the speed of the motor in an open loop case (rad/s), using the concept of encoder interrupt to calculate the speed as follows

speed = ((position - lastposition)/11*deltaT)*2*pi; //deltaT in seconds, already converted

and when I used the serial monitor or plotter to debug, I have noticed that the rotation speed is twice the expected one (around 2100 rad/s).

another question is in the following video: https://www.youtube.com/watch?v=HRaZLCBFVDE at time 6:12 where the encoder is explained, from the motor specification, the encoder has 64 counts per revolution (CPR), but when it comes to the programming part, the author uses 16 counts unstead of 64, could anyone explain to me that ?

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  • \$\begingroup\$ author uses 16 counts unstead of 64 ... why would you wait for a full revolution before checking the speed? \$\endgroup\$ Commented Aug 31 at 0:53
  • \$\begingroup\$ what about the second statement, the 22 poles ? ... what about them ? ... please do not ask vague questions \$\endgroup\$ Commented Aug 31 at 0:55
  • \$\begingroup\$ Normally, de look for high resolution so 64 is prefered over 16, I think there is a raison for that. Concerning the 22 Poles, I expect 22 pulses rather then 11 pulses per révolution. Eaxh pole should générateur a pulse. Is it the right Way to read the datasheet ? And what I have missed? \$\endgroup\$ Commented Aug 31 at 7:24
  • \$\begingroup\$ How many pulses per revolution do you actually get? I’d suspect something like a N pole generates a logic 1 and a S pole generates a logic 0. That is 11 pulses per revolution or 22 changes of state. \$\endgroup\$ Commented Aug 31 at 11:07
  • \$\begingroup\$ @learndesign no, that is not the right way to read the datasheet ... if the datasheet says 11 PPR, then that is the value ... unless you can prove experimentally that the datasheet contains an error ... you expecting something different does not make it reality \$\endgroup\$ Commented Aug 31 at 16:11

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