RoboteQ AX2850 - Manual (Page 76)

Installing, Connecting and Using the Encoder Mod-
76 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007
Cable Length and Noise Considerations
Cable should not exceed one 3’ (one meter) to avoid electrical noise to be captured by the
wiring. A ferrite core filter must be used for length beyond 2’ (60 cm). For longer cable
length use an oscilloscope to verify signal integrity on each of the pulse channels and on
the power supply.
Important Warning
Excessive cable length will cause electrical noise to be captured by the controller and
cause erratic functioning that may lead to failure. In such situation, stop operation
immediately.
Motor - Encoder Polarity Matching
When using the Encoder module for closed loop speed control, it is imperative that when
the motor is turning in the forward direction, the counter increments its value and a posi-
tive speed value is measured.
Using the PC utility, it is possible to exercise the motors and view the encoder readings.
See “Encoder Testing and Setting Using the PC Utility” on page 83.
If the Encoder counts backwards when the motor moves forward, correct this by either:
1- Swapping Channel A and Channel B on the encoder connector. This will cause the
encoder module to reverse the count direction, or
2- Swapping the leads on the motor. This will cause the motor to rotate in the opposite
direction.
Voltage Levels, Thresholds and Limit Switches
The encoder module’s input uses a comparator to reshape the encoder’s output signal. If
the signal is below a programmable threshold level, then it is considered to be 0. If above,
it is considered to be 1. The output of this comparator feeds the quadrature detector and
counters.
Ferrite Core
Encoder
FIGURE 47. Use ferrite core on cable length beyond 2’ or 60cm