54BInterface Cables
5BChapter Two: Installation
24
A ferrite collar is available (Fair-Rite part number 0443167251) and is recommended for use in
high RF environments. The collar is formed from two half-shells that snap together. The collar
should be attached to the DeviceNet cable as close as possible to the DMA unit.
You can purchase interface cables to all MKS companion products from MKS (Table 7) or,
optionally, you can make cables that meet the appropriate cable specifications. For cables
connecting to non-MKS products, you can purchase normal shielding or braided shielded cable
assemblies from MKS in a nominal 10’ (3 m) length, terminating in flying leads (pigtail) fashion
at both ends.
Table 7: Interface Cables
To Connect the DMA Unit’s analog output
to...
Use the MKS Cable...
146, 651, 652, PR4000 or 660
CBCT27-1-10
Generic Shielded Cable Guidelines
Follow the guidelines listed below if you choose to manufacture your own cables.
1. The cable must have an overall metal
braided
shield, covering all wires. Neither aluminum
foil nor spiral shielding are as effective; using either may nullify regulatory compliance.
2. The connectors must have a metal case that 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
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
the 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. 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 device.
D. Capacitance and inductance of cables that are handling fast signals (such as data lines or
stepper motor drive cables).
E. Some cables may need internal shielding from specific wires to others. Please see the
instruction manual for details regarding this matter.
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