DeviceNet is an application-level protocol used in the automation environment. It’s a digital, multi-drop fieldbus networks to connect different devices like industrial controllers, PLCs, actuators, sensors, and automation systems of multi-vendors.
DeviceNet protocol was originally developed by Allen-Bradley which is a Rockwell Automation brand, and they decided to share this new technology with others and make it an open network.
DeviceNet is now managed by Open DeviceNet Vendors Association (ODVA) an organization that develops standards and allows third-party vendors to utilize the network protocol.
DeviceNet and Its Different layers
DeviceNet follows the Open Systems Interconnection (OSI) model that uses seven layers which are Physical, Datalink, Network, Transport, Session, Presentation, and Application.
DeviceNet based on the Common Industrial Protocol (CIP), Three upper
layers of CIP starting at Session, while the bottom 4 layers have been adapted to the DeviceNet application
The “physical layer” of DeviceNet consists of a combination of cables, nodes, taps and termination resistors in a trunkline–dropline topology. We will discuss these physical components in the following articles.
For the “data link layer”, DeviceNet uses the Controller Area Network (CAN) standard that handles all the messaging between controllers and devices. The “network and transport layers” of DeviceNet establish a connection with the device by using connection IDs for the nodes, consisting of the MAC ID of a device and a Message-ID.
genius behind DeviceNet is that it joined the power and the signal into one cable, saving money and reducing the need for multiple cables which utilize more space.
3. Medium class 1
Most generally used are the thick cable for the trunk line and the thin cable for the dropline. Device Net requires two-strand pairs and a shield.
Black 0 V power supply
Red +24 V power supply
Blue CAN low signal
White CAN High signal.
Which DeviceNet cable you choose is determined by the distances and physical limitations of your application.
We can use the Round (thick or thin) cable for either trunk or droplines, the flat is used for trunk lines and the Class 1 Drop cable is used for drops.
They all use twisted pairs of wire. One pair for the 24V dc power and one pair for the signal. There is also a shield wire used in the grounding process.
The cable that you choose to fit your application will be based mainly on distance because there are specific limits to the lengths that will allow maximum data rates.
These distances are measured by two variables:
Ø “Thick” Round cable has a range of maximum length of 1,640 feet at 125 Kilobits per second to a maximum length of 328 feet at 500 Kilobits per second.
Ø “Thin” Round cable has the same maximum length of 328 feet for all three data rates of 125, 250 and 500 Kilobits per second.
Ø The “KwikLink” Flat cable ranges from 1378 feet at 125 Kilobits per second to 246 feet at 500 Kilobits per second.
Ø The “KwikLink Lite” Flat cable ranges from 1148 feet at 125 Kilobits per second to 180 feet at 500 Kilobits per second.
Total dropline length
Ø The drop lines connect the devices to the trunkline and the data rate you choose determines the total drop line length allowed.
Ø The biggest restriction for a dropline is that the maximum cable distance from any device to the trunkline is 20 feet.
Ø The maximum total drop length for each data rate is 512 feet at 125 Kilobits per second, 256 feet at 250 Kilobits per second and 128 feet at 500 Kilobits per second.
Ø Once again showing that at higher data rates you get shorter distances your network can reach, and lower data rates get you farther reaching capabilities.
DeviceNet data rates are 125, 250, or 500 Kilobits per second. The longer the length needed will result in a slower data rate and vice versa.
DeviceNet Terminating Resistors
The DeviceNet trunkline requires a 121 Ohms, 1 percent, 0.25 Watts or larger terminating resistor at each end of the trunk and directly connected across the signal wires (blue and white).
The terminating resistors reduce electrical noise and without them, in their correct place, the DeviceNet will not work properly.
The DeviceNet communications specifications are open and standardized, so a DeviceNet-compatible device from any manufacturer
can be connected.
DeviceNet can be used in a variety of field-level applications by combining devices such as Valves and Sensors.
DeviceNet Advantages and Disadvantages
The advantages of DeviceNet are low cost, widespread acceptance, high reliability, efficient use of network bandwidth and power available on the network.
The disadvantages of DeviceNet are limited bandwidth, limited message size, and maximum cable length.
It is stated over and over in many documents that 90 percent to 95 percent of all DeviceNet problems are one of two things;
1. Cabling issue.
2. You don’t have the correct EDS file registered in RSNetworx for DeviceNet.
This makes DeviceNet a great network when looking at the overall picture of that.