GE Industrial Solutions OKCV3000CN DeviceNet - Manual (Page 55)

DeviceNet
DeviceNet allows the use of either thick or thin cable to construct trunk lines. DeviceNet also allows a combina-
tion of both types of cable to be used on the same network. To determine the maximum cable distance with a mix
of both thick and thin cable, use the table below. For power restrictions with a mix of both types of cable, see the
next sections.
Data Rate Formula
125 kbaud Lthick + 5 * Lthin <= 500
250 kbaud Lthick + 2,5 * Lthin <= 250
500 kbaud Lthick + Lthin <= 100
TNetl70
where L~iCk is the length of the thick cable and Lthifl is the length of thin cable.
Drop line length is the longest cable distance of those measured from the tap on the trunk line to each of the
transceivers of the nodes on the drop line. The total amount of drop line allowable on the network depends upon
the data rate. Refer to the following table when determining the number and length of drop lines.
Data Rate Drop Line
125 kbaud
250 kbaud
500 kbaud
TNetl80
Grounding
To prevent ground loops, the DeviceNet network should be earth grounded in only one location. Grounding at
more then one location may produce ground loops, while not grounding the network will increase sensitivity to
ESD and outside noise sources. The single grounding location should be at a power tap. DeviceNet power taps
are designed to accommodate grounding. Grounding near the physical center of the network is also desired. The
physical layer circuitry in all devices is referenced to the V- bus signal. No current flow between V- and earth
ground may occur via any device other than a power supply. Some products may have more than one potential
path to ground. In these products, isolation must exist for all possible paths. If the network is already grounded,
do NOT connect the grounding terminal of the tap or ground ofthe supply to earth. If more than one supply is on
the network, then connect the drain wire/shield at ONE supply only, preferably near the physical center of the
network.
Configuring Network Power
In addition to providing communications, DeviceNet also provides power. Becausepower and signal conductors
both are contained in the cable, devices can draw power directly from the network without the need for separate
power sources.
DeviceNet has a single supply current capability of up to 16 amps using a thick cable trunk line, andup to 6 amps
using a thin cable trunk line, which makes the network highly functional and cost-effective.
The power bus capabilities for DeviceNet are:
-
Cable length as long as 500 m (1,640 feet)
-
Support for as many as 64 nodes of varying current
-
Adjustable configuration
APPENDIX D
LIE