I am using a magnetic encoders (hall sensors) which have two channels with 90º phase shift attached on a DC motor with a 61:1 gear box.
In the specification sheet of the encoder it states that the countable pulses per turn (2 edges) = 2 x 5 pulses . Is this the counts per revolution (CPR) or the pulses per revolution (PPR)?
My question is how many ticks would I get per wheel revolution (What is the pulses per revolution is for this particular magnetic encoder)?
Hall effect sensors are transducers that generate an output voltage in response to the presence of a variable magnetic field. For speed and position calculation applications, the sensors are positioned 90° apart from the full rotation circle of the motor shaft. A ferrite magnet induces the A and B signals in the sensors. Both signals are offset by 90° due to the position of the sensors in relation to the rotation circle.
In general, DC motors have a gear box (motor reducer) to give additional torque to the turn. The gearbox has a ratio of reduction of rotation depending on the model of the engine. For example in this motor is 61:1.
On the other hand, in a typical motor, the 2 signals of phases A and B of the quadrature encoder generate 22 pulses for each turn of the motor before the gearbox (in this case, as you suggest 10 pulses). After the gearbox, there is a total of 61 x 10 = 610 pulses for each revolution of the shaft.
To calculate the speed after the gearbox, the microcontroller first counts the pulses generated during a second, to multiply them by 60 and find the number of pulses per minute. Finally, to calculate the speed in RPM:
Speed in RPM= ( pulses generated during 1 second x 60 ) / 610
In regards to the pulses for each turn of the motor per gear box, as per the data sheet I attached each channel has 5 PPR, therefore I cannot simply just add the signals for a full turn. Instead a full turn is 5 PPR, and after the gearbox it is 305 and not 610 like I initially stated, right?.
Encoders have a specific number of pulses per revolution (PPR), which is related to the motor’s mechanical construction. For hall sensor encoders this depends on the number of magnet poles, and for optical encoders, it derives from the number of slots / reflective pads on the interrupter disc. I didn’t find the PPR or CPR reference in the datasheet but, yes, if each channel has 5 PPR thus, after the gearbox it will be 305 PPR.
For more encoder’s resolution information you should check encoder resolution or encoder resolution 2.
See you
