MKS T3PIA, Instruction Manual, Page: 20 / 70

Chapter Two: Installation Interface Cables
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Generic Shielded Cable Description
MKS offers a full line of cables for all MKS equipment. Should you choose to manufacture your own cables,
follow the guidelines listed below:
1. The cable must have an overall metal braided shield, covering all wires. Neither aluminum foil nor spiral
shielding will be as effective; using either may nullify regulatory compliance.
2. The connectors must have a metal case with direct contact to the cable shield on the whole circumference
of the cable. The inductance of a flying lead or wire from the shield to the connector will seriously
degrade the shield’s effectiveness. Ground the shield to the connector before its internal wires exit.
3. With very few exceptions, the connector(s) must make good contact to the controller’s case (ground).
“Good contact” is about 0.01 ohms and the ground should surround all wires. Contact to ground at just
one point may not suffice.
4. For shielded cables with flying leads at one or both ends. It is important to ground the shield at each such
end
before the wires exit. Make this ground with absolute minimum length. Refer to Figures 1 and 2.
(A ¼-inch piece of #22 wire may be undesirably long since it has approximately 5 nH of inductance,
equivalent to 31 ohms at 1000 MHz). After picking up the braid ground, keep wires and braid flat against
the case. With very few exceptions, grounded metal covers are not required over terminal strips. If one is
required, it will be stated in the Declaration of Conformity.
5. In selecting the appropriate type and wire size for cables, consider:
A. Voltage ratings.
B. Cumulative I
2
R heating of all the conductors (keep them safely cool).
C. IR drop of the conductors, so that adequate power or signal voltage gets to the controller.
D. Capacitance and inductance of cables that handle fast signals (such as data lines or stepper motor
drive cables).
E. Some cables may need internal shielding from specific wires to others.
Example 1: Preferred Method to Connect Cable
(shown on a transducer)
Transducer
Overall Insulation
(if present)
Bare Metal Cable Clamp
Making Firm Contact To Braid
Braid Here Is Desirable
(but not usually necessary)
Keep Wires and Braid
Flat Against Case
Metal Cable Clamp
Screw
Split Lock Washer
External Tooth Lock Washer
Transducer Housing
Optional Plastic or Metal Cable
Clamp (For Physical Strain Relief)
Figure 1: Preferred Method To Connect an Overall Metal Braided Shielded Cable