Appendix B – Cables
05/2008
Danaher Motion
120
S200-VTS Product Manual
Outer Shield
Motor Connector Shield
Motor W ires
Drain W ire
PE W ire
Feedback
Outer Shield
(Connect to SFD Shell)
Feedback
Inner Shield
(Connect to Logic GND)
SFD Communication
twisted pair
Optional Foil Shield Shield
SFD Return
(Inner Drain W ire
and inner shield)
SFD +5 VDC
Outer Jacket
Jacket
Inner Jacket
Composite Cable Cross-Section
There can be substantial capacitance between the power wires and adjacent feedback shield in
a composite cable. Some of the PWM ampere level spikes tend to return in this adjacent shield,
affecting the power stage voltage and current drive the feedback shield nearest to the power
wires. In a single-shielded feedback cable this driven shield is also around the feedback data
wires, so some coupling can occur. With double, concentric feedback shields, the driven shield
is the outer of the two feedback shields, and interposed between the driven shield and
feedback data wires is the inner feedback shield. Typically, the inner feedback shield is isolated
from the connector shells and is connected to the return for the power supply powering the
feedback device.
NOTE
A raw cable with two pairs of twisted, shielded feedback sections inside
a composite cable is electrically the same as single feedback shielding.
There may physically be two feedback shields in such a cable, but these
shields are not concentric. There is only one shield between the power
and feedback wires. Whereas the double, concentric feedback shields
have two shields between the power and feedback wires.
2) SFD +5 and Gnd Resistance Spec
To insure that the SFD +5 V at the SFD inside the motor is within specification, the voltage drop
total in the SFD +5 V wire and SFD +5 V RTN wire must not be greater than 0.5 V at 150 mA.
For this reason, a cable requirement is that the total resistance of the feedback SFD +5 V wire
plus SFD +5 V RTN wire must be < 3.33
Ω
(at 20° C). In practice, this means that for long
cables, the AWG wire gage needs to be considered.
NOTE
The inner shield of the a double, concentric feedback cable, when
isolated from the terminating connector shells, can also function as a
conductor to carry some or all of the SFD +5 V RTN current. This is
useful to keep the total SFD +5 and RTN resistance within specification
on long cables without having large diameters.
3) Feedback Characteristic Impedance
Danaher Motion's S200 feedback cables are designed to have a feedback data pair differential
impedance of 81
Ω
(at 1 MHz). Impedances in the range of 50 to 100
Ω
, while not tested, will
likely work properly with the S200.
Two suggestions simplify the design of customer composite cable:
1. Purchase the raw composite cable from Danaher Motion. The cable has good shielding
properties.
2. Purchase a composite feedback cable built by Danaher Motion. Review its construction,
and test its performance. There are many ways to connect the multiple shields of a composite
cable. A good way to understand how the Danaher Motion composite cable is built is to buy a
short Danaher Motion S200 composite cable, open it up, and see how the shields at both the
motor and drive end are connected.