CM4 Four-Point Continuous Monitor
CM4 Technical Manual
D-4
D.3 Cabling
D.3.1 EMC Considerations
The CM4 has been designed to comply with applicable EMC standards
at the time of manufacture. The design includes filtering, shielding, and
bypassing techniques. At the time of certification, simulated customer
Input/Output (I/O) schemes were tested.
All methods used in your equipment for emission suppression
and reduction of susceptibility are interactive. Modifications to the
instrument will most likely result in increased emissions and higher
vulnerability to other radiated fields.
Following the guidelines in this EMC Considerations section will ensure
your instrument maintains the highest degree of EMC integrity. The
guidelines listed apply only to I/O emissions, and do not apply to A.C.
and D.C. instrument power connections.
Cabling
At a very minimum, all cables should include a braided shield. Ideal
results have been obtained with twisted pair cabling which has a foil
shield surrounding each pair plus foil and 90% braid shielding around
the bundle. While this can be expensive, it yields the best results. In
addition, ensure local electrical code requirements are met.
Cabling Type
The following cable parameters must be considered:
Braided Shield
Must have a minimum 90% coverage
Foil Shield
When used with braid, provides 100% coverage.
NOTE
Do not use foil alone. It has a tendency to break.
Twisted pair
Provides good immunity to magnetic pickup in RS-422
and RS-485 data lines.
Stranded Pair
Stranded wire Provides the greatest surface area. MDA
Scientific product testing uses >90% braid with foil
(around the bundle); twisted pair; stranded 24 AWG
(minimum wiring for all qualification and certification
testing.
Examples:
Belden 83652 2-conductor
Belden 83653 3-conductor
Belden 83654 4-conductor
Belden 83656 6-conductor
All examples are 18 AWG stranded, with 100% shield
coverage
Shield
Termination
Only one end of the shield is to be connected to earth
ground. This connection is to be made at the Model
CM4. Continuation of this shield to the earth ground is
very important.
For discrete wire terminations, pigtails to the cabinet
(connector) ground should be extremely short
(absolutely no greater than three inches).
For multiconductor connector terminations, only 360°
shielded shells should be used.
Connectors
All qualification and certification of MDA Scientific products were
achieved with high quality connectors, providing 360° shield coverage.
These connectors generally had metal shells.
Failure to properly secure the connector to the equipment will result in
high emission levels. Also, poorly constructed or improperly assembled
connectors can be a high source of radiated noise, and provide a path
for external signals into the instrument.
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