Chapter Two: Installation Interface Cables
11
Interface Cables
Use a CB649S-1-Mx or CB649-1-Mx cable (where x indicates code for the length) to connect the
649 controller to an MKS Type 247 or 246 Mass Flow Controller Power Supply/Readout or a
Type 647 Mass Flow and Pressure Programmer/Display unit. The standard cable, CB649-1-M1
is 10 feet in length.
Note
To order a metal braided shielded cable, add an “S” after the cable type
designation. For example, for an overall metal braided shielded cable
order CB649S-1 for; order CB649-1 for a non-shielded cable.
Generic Shielded Cable Description
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. (A
6.35 mm 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.
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