eBook: Automating Manufacturing Systems; with PLCs
   



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28.4 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 2: 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

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