When we talk about process automation communication protocols, there are a number of names that come in our mind. Out of them, one of the common ones is analog. From digital communication protocols, HART, FOUNDATION Fieldbus, and PROFIBUS PA usually come up first. However, there are other ways to integrate a field device to a control system that may suit our application, and this article talks about such a protocol.
What is DeviceNet?
DeviceNet is a low-level application-layer communication protocol for industrial use. We can connect up to 64 nodes to a DeviceNet network. Each node can contain simple sensors or more complex gadgets such as a programmable logic controller (PLC).
DeviceNet uses the Controller Area Network (CAN) standard, a standard for intelligent devices to communicate with each other. This network also allows for different topologies, cables, and more.
DeviceNet applications and setup
DeviceNet uses a trunkline-dropline topology (more on that later), where small lines connect devices to the main line. These small lines should not run more than six meters from the trunkline.
As a loop-powered gizmo, DeviceNet can supply power to many devices directly from its cables, depending on their power needs. It also supports various data exchanges such as cyclic, polled, and strobed. For setup, we can choose between multi-master or master-slave.
The network can include up to 64 nodes, and end-to-end points will depend on your baud rate:
- 125 kilobytes per second (Kbps) – 500 meters
- 250 Kbps – 250 meters
- 500 Kbps – 100 meters
DeviceNet uses common industrial protocol (CIP) for its upper layers. The CIP follows the open systems interconnection (OSI) model in seven layers: physical, data link, network, transport, session, presentation, and application.
Usually, we encounter DeviceNet networks with valve actuators, push buttons, detection sensors, and so on. We’ll rarely find pressure, level, or flow devices in a DeviceNet network. But a few will use converters, and we’ll sometimes find a flow meter with DeviceNet integrated.
To know more about HART Communication, you can read the Visaya Article on HART Basics
With DeviceNet, we can structure the network in many ways. However, we need to know its limitations. DeviceNet uses a trunkline-dropline topology on a loop-powered network with 24 volts of direct current and 8 amps. With its loop power, we can run low-energy devices. However, if our device requires more juice than the network provides, we´ ll need an external power supply. In that case, the network will only serve for communication.
The length of the network will depend on the network speed, as mentioned in the last section, and the type of cables we use. For instance, if we have a flat cable, the trunk distance for a baud rate of 125 Kbps will have to stay within 420 meters. So 250 Kbps needs 200 meters, and 500 will go to 75 meters. We can choose between a round thick cable, round thin cable, and others to modify these numbers.
To set up a DeviceNet network, we’ll only need a couple of simple math equations. However, we definitely need to consider the cable type, device energy consumption, current, and other specs to do the math.
DeviceNet EDS files
EDS stands for electronic datasheet. Like a physical datasheet, a device’s EDS file will give us all the relevant information you need on the device. So we have to have it in our configuration tool to know which device we have connected to the network and what parameters it has. We’ll find these files in many other field networks besides DeviceNet too.
Let’s say we want to set up a HART device. So the configuration tool needs the EDS file for that specific device. If the tool uses PROFIBUS for its protocol, then we will need the EDS files for that device on that protocol.
DeviceNet works the same way. Vendors must provide the proper files for their devices that use DeviceNet as their protocol. Often we’ll have to download this file from a vendor’s website, then upload it to the system.
To know about Wireless, you can read the Visaya Article on Configuring Wireless HART
The way we configure the DeviceNet devices can vary by factors such as the type of control system you have. However, we can give you an overview to point you in the right direction.
As mentioned before, you can have up to 64 nodes on your network. Each node has its own media access control identifier or MAC ID.
When you purchase a device for DeviceNet, it should have a MAC ID. After you set up the device, you also have to set the network where you plan to install it. You’ll need other data such as the class identifier, instance identifier, and attribute identifier as well.
After that, go to the control system and add the DeviceNet scanner. Then the software will browse the network, find all devices connected to the driver, and so on.
Remember to check the MAC IDs of the devices too. If we find duplicates, we’ll have to change one of the addresses before we can finish the installation.
DeviceNet error codes
We can use DeviceNet error codes either for corrective or preventive maintenance. We can buy specific tools for the DeviceNet network from a number of vendors, like NetAlert for DeviceNet, DeviceNet Detective 2, and others. This is probably the easiest way for most users.
Or we can use the good old multimeter to verify the network. This method will require more knowledge, but we can still do it. So if we found an error code and want to use the first method, then we can get the following:
- Errors – The tool can locate errors and show relevant data for easy analysis, such as minimum or maximum rate and total errors. We can also find and identify errors by nodes.
- Traffic – Studying traffic messages (bandwidth by errors, bus frames per second, etc.) can tell us if we have too many devices on one network. Then we can move them to other networks to reduce the data volume.
- Voltage – We should check this in the field where we have a device installed. Measuring the peak-to-peak value or minimum and maximum may point the way to the problem.
We can also gather more data with DeviceNet analyzer tools or multimeter, like shield voltage, voltage differential between recessive and dominant, and so on. Somewhere in all this data, we can find our answer.
To know about Profinet, you can read the Visaya Article on the difference between Profibus and Profinet
Using PROFINET with DeviceNet
Can we use a PROFINET gateway with DeviceNet? Short answer: Yes!
Say we need to integrate more than one network into a control system. It happens quite often. We can choose to have one network in the field and another at the control system level. For that, we can use bridges or converters.
We can also have a clear connection between the control system and the field devices. For example, if we want PROFIBUS but have HART field devices, then we can use the HART over PROFIBUS concept. In this structure, we have a coupler converting the HART signal for the PROFIBUS. We can also set up devices remotely.
If we have a DeviceNet network in the field but want to connect it to a PROFIBUS control system, the market offers several options. We can also check these options and read the specs to see how they might work for you:
- Anybus X-gateway – DeviceNet, PROFINET-IRT device
- Hilsher – Gateway DeviceNet to PROFINET IO devices
- ADF Web – HD67608 PROFINET/DeviceNet converter
To know more about DeviceNet, you can get in touch with our engineers and we will be happy to help.