Ethernet. Is it time to make the switch?

Ethernet is becoming the standard for industrial automation. Its ability to connect devices from a small cell to entire plant lines communicating simultaneously has caused a tremendous shift in the need for Ethernet in the constantly changing industrial environment.

 

ETHERNET-IP SYSTEMS

There are many networks using ethernet physical layer, while the protocol for sending and receiving data will change by the communication protocol of the device. Common protocols using a ethernet (RJ45) physical cable include EthernetIP®, Profinet® and EtherCAT®

 

BENEFITS

-Explicit messaging communication between scanner and slave device allowing for a much more robust error handling and diagnosing of module status. It is even possible on some devices to

-255 devices per ring instead of the common 64 node limit of BUS devices, such as DeviceNet. This means that there are 256 possible addresses (fourth octet) for each third octet defined.

-Each device generally has a webpage that is accessible through a web browser(by using its IP address) that contains useful information such as module status and even user manuals on some devices.

-Loss of communication to a node will not drop the entire network. The module communication loss should generally stop automatic function, but this must be programmed.

-Ethernet communication between Cell and Line PLC controllers and the Plant network means that Plant diagnostics (uptime, errors, faults) and part tracking (VIN, part counts, etc) is possible through ethernet messaging between the PLC and the Host Network.


DRAWBACKS

-Each EthernetIP module installed will generally require 2 cables, 1 for communication (Ethernet) and 1 for power supply (usually 24V). This may increase the amount of cabling required, compared to BUS networks.

– There is also the need for the addition of a managed switch to control latency in time sensitive applications or when CIP Safety applications are involved. The difference between a managed and unmanaged switch (Short version) is that an unmanaged switch is just routes traffic packets, where a managed switch can actually control the flow of packets and even block specific packets in some cases (public/private divider).

-Understanding of networking is critical to device communication, there are many other factors to communication, such as subnet mask and default gateway. Other setups have specific devices on the Public network for example 120.111.11.123 and some may be private (internal ring to PLC only) 192.168.1.123 (most common private network), regardless of public network address.

 

LEGACY SYSTEMS 

There are many legacy networks using DeviceNet®, ProfiNet® or ControlNet® for cost reasons or to maintain a standard. This comes into play with larger plants that wish to keep specific areas with the same technology in order to make it easier to maintain, because the same modules and cables can still be used on new or old cells.


BENEFITS

-Reduced wiring between the scanner and the slave devices (normally daisy chained as a ring) because the power (24+ and 0V) and signal (CAN + and CAN -) are included in the same cable.

– BUS Networks are generally cheaper because of flooded ethernet market demand.

– Specific devices can still support CIP Safety functions on the cheaper BUS network.

– Devices are easier to setup and only require a node address and communication/power cable.


DRAWBACKS

– The network requires terminating resistors to determine communication node ends.

– BUS Networks use differential voltage communication in order to send packets, making them more susceptible to noise (EMF interference).

– Loss of communication in one device can be difficult to troubleshoot as it normally causes the entire network to drop communications. The best method is to quarter the network with a terminating resistor until the network is up and then find the node in the last quarter section.

– Communication issues not related to physical wiring or cabling is much more difficult to diagnose, requiring an oscilloscope in some cases.

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