Delta Tau 5xx-603869-xUxx - Manual (Page 44)

Brick Motion Controller Hardware Reference Manual
36 Appendix A
Type of Cable for Encoder Wiring
Low capacitance shielded twisted pair cable is ideal for wiring differential encoders. The better the shield
wires, the better the noise immunity to the external equipment wiring. Wiring practice for shielded cables
is not an exact science. Different applications will present different sources of noise, and experimentation
may be required to achieve the desired results. Therefore, the following recommendations are based upon
some experiences that we at Delta Tau Data Systems have acquired.
If possible, the best cabling to use is a double-shielded twisted pair cable. Typically, there are four pairs
used in a differential encoder’s wiring. The picture below shows how the wiring may be implemented for
a typical differential sinusoidal encoder using double shielded twisted pair cable.
SIN+
SIN-
SHIELD
COS+
COS-
SHIELD
INDEX+
INDEX-
SHIELD
ENC PWR
GND
SHIELD
OUTER
SHIELD
EXAMPLE OF DOUBLE SHIELDED
4 TWISTED PAIR CABLE
The shield wires should be tied to ground (Vcc return) at the interpolator end. It is acceptable to tie the
shield wires together if there are not enough terminals available. Keep the exposed wire lengths as close
as possible to the terminals on the interpolator.
Note:
It has been observed that there is an inconsistency in the shielding styles that are
used by different encoder manufacturers.
Be sure to check pre-wired encoders to ensure that the shield wires are not
connected at the encoder’s side. Shield wires should be connected only on one
side of the cable.
If the encoder has shield wires that are connected to the case ground of the
encoder, ensure that the encoder and motor cases are sufficiently grounded. Do
not connect the shield at the interpolator end.
If the encoder has pre-wired double shielded cable that has only the outer shield
connected at the encoder, then connect only the inner shield wires to the
interpolator. Be sure not to mix the shield interconnections.
One possible cable type for encoders is Belden 8164 or ALPHA 6318. This is a 4-pair individually
shielded cable that has an overall shield. This double-shielded cable has a relatively low capacitance and
is a 100
Ω impedance cable.
Cables for single-ended encoders should be shielded for the best noise immunity. Single-ended encoder
types cannot take advantage of the differential noise immunity that comes with twisted pair cables.