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NETWORK COMPARISONS
No one network is ideal for solving all controls problems. Table 1 shows a variety of network types and criteria. Generally there is a tradeoff between length, speed, cost, and reliability. For example, slower networks such as Controlnet/Devicenet, Lonworks, Modbus, and Profibus are designed to be highly predictable (deterministic) and work well between a central processor and distributed IO modules. Other network types such as Ethernet provide a low cost alternative for connecting IO components but it can be susceptible to electrical noise. Other network types such as Sercos are designed for motion control systems and provide outstanding interoperability between manufacturers.
Table 1: Network Comparison
|
Network
|
topology
|
addresses
|
length
|
speed
|
packet size
|
|
Bluetooth
|
wireless
|
8
|
10
|
64Kbps
|
continuous
|
|
CANopen
|
bus
|
127
|
25m-1000m
|
1Mbps-10Kbps
|
8 bytes
|
|
ControlNet
|
bus or star
|
99
|
250m-1000m wire, 3-30km fiber
|
5Mbps
|
0-510 bytes
|
|
Devicenet
|
bus
|
64
|
500m
|
125-500Kbps
|
8 bytes
|
|
Ethernet
|
bus, star
|
1024
|
85m coax, 100m twisted pair, 400m-50km fiber
|
10-1000Gbps
|
46-1500bytes
|
|
Foundation Fieldbus
|
star
|
unlimited
|
100m twisted pair, 2km fiber
|
100Mbps
|
<=1500 bytes
|
|
Interbus
|
bus
|
512
|
12.8km with 400m segments
|
500-2000 Kbps
|
0-246 bytes
|
|
Lonworks
|
bus, ring, star
|
32,000
|
<=2km
|
78Kbps-1.25Mbps
|
228 bytes
|
|
Modbus
|
bus, star
|
250
|
350m
|
300bps-38.4Kbps
|
0-254 bytes
|
|
Profibus
|
bus, star, ring
|
126
|
100-1900m
|
9.6Kbps-12Mbps
|
0-244bytes
|
|
Sercos
|
rings
|
254
|
800m
|
2-16Mbps
|
32bits
|
|
USB
|
star
|
127
|
5m
|
>100Mbps
|
1-1000bytes
|
|
|