Over View of Device Net

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Over View of Device Net

• Meliah Mayer
• ELPT 2449
• Industrial Automation
• Spring 2007

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Device Net

• Device net was designed to replace large,
  complex wiring schemes with a simple trunk and
  branch structure, while also providing a
  high-level of diagnostics to each device on the
  network.

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(No Transcript)
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Characteristics of Device Net

• Based on CAN (controller area network)
• Maximum number of devices 64
• Baud rate 125, 250, 500kbits/sec
• Distance 100M to 500M
• Maximum message size 8 bytes of data
• Messaging formats polling, strobe, cyclic, and
  COS (change of state)

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Polling

• The scanner asks each device to send or receive
  an update of its status. This requires and
  incoming and outgoing message for each node on
  the network. Polling is more precise but least
  time efficient way to request information from
  the device.

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Strobing

• The scanner broadcasts a request to all devices
  for a status update. Each device responds in turn
  sequentially. Node numbers can be assigned to
  prioritize messages.

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Cyclic

• Devices are configured to automatically send
  messages on scheduled intervals. This is
  sometimes called a heartbeat and is often used
  in conjunction with COS messaging to indicate
  that the device is still functioning.

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Change of State

• Devices only send messages to the scanner when
  their status changes.This occupies the minimum
  time on the network, but does change the
  throughput and response time from deterministic
  to statistical.

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Connection Speed and Cable Length

• Baud rate
• The rate of speed which data is being transmitted
  over the network
• 500kb
• 250kb
• 125kb default

• Cable length
• The speed of the data being transmitted affects
  the length of cable
• 100m or 328ft
• 250m or 820ft
• 500m or 1680ft

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Device Net Addresses

• Each device on the network must have a unique
  address.
• An integer is assigned to each device which we
  call a MacID (media access identifier).
• There are a maximum of 64 nodes on a device net
  network.
• MacID 63 is the default address of new devices.

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Devices for Device Net

• Personal Computers
• Operator interface stations
• Motor starters
• Barcode readers
• Sensors
• Scanner cards
• Push buttons

• PLC (programmable logic controllers)
• Drives (AC DC)
• Limit switches
• Servos
• Block I/O
• Motion control devices

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Devices we have installed on our network

• Since we are automating a conveyor system, we
  need powered roller controllers to move the
  product down the assembly line.
• We also need sensors to activate our powered
  roller controllers and out lift stations.
• We also need tower lights to give the operators a
  visual indicator if the system has a problem.

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Powered Roller Controller
The brown wire is not used
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Sensors
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Tower Lights
The tower light is connected using all five wires
and the connections are color coded for easy
installation and wiring.
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Setting up a Device Net Network

• Add one device at a time.
• Make sure it is working correctly
• Space out your address so that you can add
  devices later on when updating your system.
• Make sure your master/slave configuration is set
  up correctly.

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Trouble Shooting Guidelines

• Make sure all Baud rates are the same on every
  device installed.
• Make sure all MacIDs are not duplicated.
• Nine times out of ten, if you are working on a
  device and experience a problem it is usually the
  device you are working on.
• If all of the above is good. Recycle the power
  supply.