What is DeviceNet?
DeviceNet is an example of a device-level local area network (LAN). DeviceNet is an open device-level network. It is relatively low speed but efficient at handling the short messages to and from I/O modules.
DeviceNet brings LAN technology down to the lowest level of the manufacturing enterprise on the shop floor.
Why is DeviceNet needed?
The PLCs are becoming more powerful by increasing the capablity of the number of the device can be connected, so the Conventional systems have racks of inputs and outputs with each I/O device wired back to the controller.
The DeviceNet protocol dramatically reduces costs by integrating all I/O devices on a 4-wire trunk network with data and power conductors in the same cable. This direct connectivity reduces costly and time-consuming wiring.
Features of DeviceNet:
The basic function of a DeviceNet I/O bus network is to communicate information with, as well as supply power to, the field devices that are connected to the bus. The PLC drives the field devices directly with the use of a network scanner instead of I/O modules.
- Read inputs from a device.
- Write outputs to a device.
- Download configuration data.
- Monitor a device’s operational status.
The scanner module communicates with the controller to exchange information which includes:
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Device I/O data
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Status information
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Configuration data
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DeviceNet also has the unique feature of having power on the network. This allows devices with limited power requirements to be powered directly from the network, further reducing connection points and physical size.
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DeviceNet uses the Common Industrial Protocol, called CIP, which is strictly object-oriented.
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Two different types of objects are defined in the CIP specification: communication objects and application-specific objects.
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A DeviceNet network can support up to 64 nodes and the network end-to-end distance is variable, based on network speed.
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Typical layout of the trunk wiring for a DeviceNet network:
- Communications data is carried over two wires with a second pair of wires carrying power.
- The field devices that are connected to the network contain intelligence in the form of microprocessors or other circuits.
- These devices can communicate not only the on/off status of field devices but also diagnostic information about their operating state.
Advantages of DeviceNet:
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Faster installation times
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Less expensive compared to traditional point-to-point wiring.
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DeviceNet devices can sometimes offer more control features compared to traditional/switched devices.
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DeviceNet technology can be used with either PLC or PC-based control systems.
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Most devices provide useful diagnostic information which can make systems easier to troubleshoot and minimize downtime.