15. Industrial Networking

TOPIC 1: Network Types

There are several different types of common networks used in industrial automation.

1.  DeviceNet – Originally developed by Allen-Bradley, DeviceNet uses the CAN protocol for communication.  After it gained popularity, Allen-Bradley released the protocol so that now any company can develop equipment that uses DeviceNet.  This protocol can have up to 64 nodes on a network and can have a physical cable length of up to 500 meters.

2.  Ethernet Industrial Protocol or Ethernet/IP – This is an industrial version of ethernet developed by Rockwell Automation and also released as an open protocol.  The limitations of this technology are similar to standard ethernet.

3.  PROFIBUS – Stands for Process Field Bus and uses the PROFINET protocol for communication.  While it is an open protocol, this protocol is owned by PROFIBUS & PROFINET International.  It is similar to ethernet.

4.  ControlNet – Is another protocol developed by Allen-Bradley and can utilize up to 99 nodes with a network length of 1000 meters.  It also supports redundant cabling and is able to support very precise timings of messages sent.

5.  Interbus – Interbus was developed by Phoenix Contact and is widely used with industrial sensors.  It is not as common in general automation systems but when there are many sensors being used it may be given consideration.

Many industrial applications will contain more than one type of network.  For example, in one facility the robot is part of a small DeviceNet network with a few sensors and safety devices along with a PLC.  This PLC is also a part of a bigger network, Ethernet/IP, that gets information to the plant level control system.  This configuration consists of one Ethernet/IP network with several smaller DeviceNet networks and it uses the PLC as the bridge between the two.

TOPIC 2: In the lab

In our laboratory, we have one large Ethernet/IP network.  However, each robot also has a small DeviceNet network through which it is interfaced to two other devices for a total of three devices on each DeviceNet network.  On this network there is the robot, an RFID system, and a Compact Block I/O device.  The CompactBlock I/O device is the device which allows our robots to have connections to real-world digital inputs and outputs.  The robot does not have actual inputs and outputs, rather it has a DeviceNet network connection.  In the software, a DeviceNet network address is tied to virtual inputs and outputs.  The DeviceNet network address for the RFID system is 5 and the network address for the CompactBlock I/O is 13.  In software, the robot’s virtual inputs 33-40 are tied to network address 13 which is why we use input 33 in code when referring to input 0 on the CompactBlock I/O.

The DeviceNet network cable consists of five conductors; transmit, receive, DC+, Ground, and a shield drain wire.  According to the DeviceNet protocol, the termination to each node must include a 120 Ohm resistor between the transmit and receive cables.  However, sometimes this resistor is included in the device to which the cable must connect and sometimes it is required externally.  Both the robot and the CompactBlock I/O require external resistors, the RFID system does not.

You should now be prepared to answer the following questions.

  1. A DeviceNet network can contain a maximum of ____ node.
  2. Ethernet/IP was originally developed by ______________.
  3. True or False?  Each manufacturing facility selects one type of network and they use them exclusively throughout their facility.
  4. The RFID system used in the laboratory is made by ______.
  5. The CompactBlock I/O used in the laboratory is made by _____.
  6. In the laboratory, the CompactBlock I/O is on the DeviceNet and has what address?
  7. DeviceNet must be terminated at each node with a _____ ohm resistor.

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