Woodward 2301E, Инструкция по установке и эксплуатации, Страница: 36 / 182

2301E Digital Control Manual 26641
26 Woodward
Termination
For RS-422, termination should be located at the receiver when one or more
transmitters are connected to a single receiver. When a single transmitter is
connected to one or more receiver, termination should be at the receiver farthest
from the transmitter. Figure 2-5 is an example.
Figure 2-5. RS-422 Terminator Locations
Grounding and Shielding
The RS-422 specifications state that a common/RS-422 ground wire is needed if
there is no other ground path between units. The RS-422 on the 2301E is
isolated, so there is no other path for common other than wiring to the pin.
The preferred method for common wiring is to include a separate wire in the
cable that connects the circuit grounds at each port together with a dedicated
wire inside the cable shield.
If the total cabling is > 30 m (typical), the preferred shield connection is to
connect the shield to earth ground (chassis) at one point (most critical port),
using a capacitor to terminate the shield at the remaining ports. If the total
cabling is < 30 m, connect the shield directly to the earth ground at each port.
The alternate, less robust, way to connect shield and common is to connect all
circuit grounds/commons at each port to the shield instead of a separate wire,
and then connect the shield to earth ground at one point (most critical port), using
a capacitor to terminate the shield at the remaining ports.
If there are non-isolated nodes on the party line, connect the shield to earth
ground at a non-isolated node, not at an isolated node. Figures 2-6 and 2-7
illustrate these cabling approaches.
Non-isolated nodes may not have a signal ground available. If signal
ground is not available, use the alternate wiring scheme in Figure 2-7
with the signal ground connection removed on those nodes only.