Rockwell Automation Publication 520-UM001I-EN-E - July 2016 217
Encoder/Pulse Train Usage and Position StepLogic Application Appendix E
Determine Encoder Pulse Per
Revolution (PPR)
Specification Based on Speed
Resolution
Use the following formula to determine the encoder pulse per revolution (PPR)
specification based on the speed resolution.
Example 1
To determine the PPR for quadrature encoder, to achieve 0.06 Hz of speed
resolution on a 4-pole motor (2-pole pair) with a base speed of 60 Hz:
Therefore, select 8333 PPR or higher for the quadrature encoder to achieve the
desired speed resolution of 0.06 Hz.
Example 2
To determine the speed resolution, using a 1024 PPR quadrature incremental
encoder on a 4-pole (2-pole pair) motor:
Therefore, using a 1024 PPR quadrature encoder will give a speed resolution of
0.49 Hz.
A quadrature encoder provides rotor speed and direction. Therefore, the
encoder must be wired such that the forward direction matches the motor
forward direction. If the drive is reading encoder speed but the position
regulator or other encoder function is not working properly, remove power to
the drive, then do one of the following:
• Swap the A and A (NOT) encoder channels.
• Swap the B and B (NOT) encoder channels.
• Swap any two motor leads.
Drives will fault when an encoder is incorrectly wired and A535
[Motor Fdbk
Type] is set to 5 “Quad Check”.
The operating speed range will depend on the motor control mode selected
(SVC or VVC). For more information, see Performance with Encoder
on
page 170.
Speed resolution (Hz) =
1
encoder pulse number x 4
10
-3
sec
x pole pairs
0.06 Hz =
= ~8333 pulse
1
encoder pulse number x 4
10
-3
sec
x 2
Speed resolution (Hz) =
1
1024 x 4
10
-3
sec
x 2
= 0.49 Hz
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