Chapter Two: Installation How To Un
ack the 146 Instrument
25
Interface Cables
As of January 1, 1996, most products shipped to the European Community must comply with the
EMC Directive 89/336/EEC, which covers radio frequency emissions and immunity tests. In
addition, as of January 1, 1997, some products shipped to the European Community must also
comply with the Product Safety Directive 92/59/EEC and Low-Voltage Directive 73/23/EEC,
which cover general safety practices for design and workmanship. MKS products that meet
these requirements are identified by application of the CE mark.
To ensure compliance with EMC Directive 89/336/EEC, an overall metal braided shielded cable,
properly grounded at both ends, is required during use. No additional installation requirements
are necessary to ensure compliance with Directives 92/59/EEC and 73/23/EEC.
Refer to
Appendix B: Parts List/Accessories,
page 303, for a complete list of interface cables
available.
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 which has direct contact to the cable’s 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. The shield
should be grounded to the connector before its internal wires exit.
3. With very few exceptions, the connector(s) must make good contact to the device’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 at each such end,
to ground the shield
before
the wires exit. Make this ground with absolute minimum
length. Refer to Figures 2 and 3, page 26. (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’s 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 or in the
instruction manual.
5. In selecting the appropriate type and wire size for cables, consider:
A. The voltage ratings;
B. The cumulative I
2
R heating of all the conductors (keep them safely cool);
C. The IR drop of the conductors, so that adequate power or signal voltage gets to the
device;
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