CANopen expands over Ethernet

Written by: Tom Shelley | Published:

Ethernet and Fieldbus Special Report

One of the increasingly popular Ethernet based open standards is Ethernet Powerlink or CANopen over Ethernet.

Originally a proprietary standard developed by Bernecker and Rainer, it combines the low cost and convenience of Ethernet hardware, with software suitable for real time automation control.

Thomas Hopfgartner, a controls expert with Bernecker and Rainer says: "Whereas Ethernet was originally a collision based protocol, Ethernet Powerlink has a master that controls a polling system that provides time slices for answers so that you can make it deterministic."

The software is based on another open standard, CANopen. This was originally developed for automotive systems. Powerlink uses the same device description files as CANopen, the same Object Dictionaries and the same communication mechanisms such as Process Data Objects, Service Data Objects, and Network Management. All CANopen applications and device profiles can be used in Powerlink environments.

Due to close cooperation between CAN in Automation (CiA) and the Powerlink Standardisation Group, many CANopen service providers also provide Powerlink solutions and products.

It currently boasts 0.1µs system synchronisation, 100Mbit/s bandwidth and 100µs cycle time, although he said that achieved cycle times in reality were 30, 40 or 50ms and the system was installed on about 20,000 machines.

The system will work with 240 nodes, which can in practice mean 480 synchronised axes, and there can be up to 100m to 2km between nodes.

Networks can have a star, tree, daisy chain or ring structure or any combination of these topologies. Powerlink provides unrestricted support for hot plugging.

Communication does not have to go through the multiple nodes, which enables the construction of decentralised safety architectures. A special protocol, Powerlink Safety can be implemented in systems requiring SIL 3 protection.

Pointers

* Powerlink is a flexible architecture based on Ethernet hardware and CANopen software

* It is an open standard, available to anyone who cares to use it, with a standardisation group as well as a user group

* It currently has about 70 members including several of the leading 'blue-chips' in automation

Collaboration advances with management Ethernet

According to Mark Daniels, a product manager at Rockwell: "Our relationship with Cisco is beginning to bear fruit."

The collaboration began in 2005 with the aim of achieving unprecedented levels of visibility, flexibility, and simplification of functionality, technology and systems.

"We are increasingly seeing people adopt industrial Ethernet on the shop floor," says Daniels.

However, according to Clive Barwise, integrated architecture field business leader at Rockwell, "there is a definite disparity in the manufacturing environment between the production/control and IT departments regarding the use of Ethernet/IP. Essentially, Rockwell Automation is the expert in the control space and
Cisco is the expert in the IT and Ethernet space."

Rockwell has worked with Cisco to develop the right combination of products and can guide customers to the right way of deploying Ethernet architecture.
Security is still an issue, particularly for utilities. However, the water industry is said to be very keen on the technology.

The key hardware product is still the Stratix 8000 modular managed switches, which have a Rockwell badge on them but are manufactured by Cisco. But since then, the two companies, have developed reference architectures to assist implementation and successful deployment.

PLCs and interfaces understand all protocols

A new range of micro PLCs and HMIs have shown excellent capability to communicate using any of the standard high and low level protocols.

Mitsubishi's FX3G controllers are not only small, 90mm high and 86mm deep, and cost less than £300 each, but are also versatile.

On the left hand side of the CPU units are the ADP or Adapter bus. This allows the attachment of up to four additional modules: two RS-232 or RS-485 interface modules and two analogue adapters, including a temperature acquisition module for Platinum1000 and Nickel1000 elements.

On the right hand side, one can add modules for connection to: CC-Link, Modbus, Frequol, Profibus, OPC, CANOpen, DeviceNet, ASi and Industrial Ethernet networks. Additional expansion slots are available on the front of the unit, where up to two expansion boards can be inserted to add serial RS-232, RS-422 or RS-485 and analogue functions.

In addition, Roger Tasker, product manager for the FX3 series explained that since there are still old Mitusbishi PLCs functioning 25 years after they were installed, a useful ability is to be able to take a programme out of an old S series unit, convert it using DOS Medoc software to a program suitable for Windows software. This can then be loaded into one of the new controllers. Other specifications are 14 to 128I/O, expandable to 256I/O with a serial network. This is with 0.21µs per step and it has the ability to store 32,000 programming steps.

A Graphic Operator Terminal (GT) 1000 HMI, start from under £200 for a 3.7 inch screen. These are able to cope with a wide range of protocols, so they can work with a multitude of systems as well as those made by Mitsubishi.

Unlike a three-colour beacon, which does not cost that much less, a small HMI is not able to flash. But, it can tell an operator what has caused a problem.
Tasker said that in addition, the top end HMIs, which go up to a 15 inch touch screen, can record up to 120s of video before an even and 120s afterwards, so an operator can see what led up to an event visually.

Furthermore, they can also be made to hold manual and video animation on how to put problems right.

As Tasker says: "Who can quickly find paper manuals five years after a system has been installed?"

Safety moves into mainstream

Pilz, best known for its pioneering work in safety systems for automation, has integrated its safety technology into a new range of general automation control products.

Richard Chapman, an engineer at Pilz, says: "The Automation System PSS4000 combines, standard, safety and motion control, and diagnostics and visualisation using one communication system for all areas."

Hardware, all in Pilz bright yellow enclosures, consists of combinations of a PSSuniversal PLC, PSSuniversal multi and PSSuniversal I/O units, all linked by real time Ethernet SafetyNET p communications, which supports both the Real-Time Frame Line (RTFL) format for fast communication in dynamic applications and the Real-Time Frame Network (RTFN) format to allow communication via any Ethernet network.

This includes traffic from other industrial Ethernet versions, laptops, and video. When using a SafetyNET p RTFL and the SafetyNET p protocol chip, a real-time scan time of 62.5 µs is supported.

The system will be available generally later this year. In the mean time, the company is looking for more locations for field trials, which will be free to users. So far, in the UK, the system has been applied to a high-speed packaging and a printing line.


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