RoboteQ AX2850 - Manual (Page 73)

AX2550 Motor Controller User’s Manual 73
Installing the Encoder Module
Specifically, the encoder module can process 250,000 counts per seconds. As discussed
in the previous section, a count is generated for each transition on the Channel A and
Channel B. Therefore the module will work with encoders outputting up to 62,500 pulses
per second.
Commercial encoders are rated by their numbers of “Pulses per Revolution” (also some-
times referred as “Cycles per Revolution). Carefully read the manufacturer’s datasheet to
understand whether this number represents the number of pulses that are output by each
channel during the course of a 360o revolution rather than the total number of transitions
on both channels during a 360o revolution. The second number is 4 times larger than the
first one.
The formula below gives the pulse frequency at a given RPM and encoder resolution in
Pulses per Revolution.
Pulse Frequency in Hz = RPM / 60 * PPR * 4
Example: a motor spinning at 10,000 RPM max, with an encoder with 200 Pulses per Rev-
olution would generate:
10,000 / 60 * 200 * 4 = 133.3 kHz which is well within the 250kHz maximum supported by
the encoder module.
An encoder with a 200 Pulses per Revolutions is a good choice for most applications.
A higher resolution will cause the counter to count faster than necessary and possibly
reach the encoder module’s maximum frequency limit.
An encoder with a much lower resolution will cause speed to be measured with less preci-
sion.
Installing the Encoder Module
The Encoder module is available in kit form for installation by the user inside the AX2550
controller. It may also be ordered factory-installed in the controller by using the product ref-
erence AX2850.
FIGURE 42. Encoder Module for AX2550. Factory installed in AX2850