Wireless networking for automation systems undoubtedly sounds attractive. Reduced wiring and simplified access to often hard-to-reach places are obvious benefits. However, it is also important to remember that wireless networking devices still cost rather more than their wired counterparts.
Nevertheless, there are applications where the use of wireless technology is not only justified, but sometimes even the only option. A good example is moving equipment working in a constrained environment. It may be possible to supply power by some form of sliding contact or slip ring arrangement, but this type of connection is of little use for the reliable transmission of data.
Another example is a stacker truck in an automated warehouse. This is powered by its own on-board batteries, but still needs to communicate with the automation system to receive routing data and to report back status information.
As these examples show, there is clearly a need for wireless technology, but implementing it successfully is far from straightforward. Automation systems usually have to function in areas where there are high levels of electrical interference, such as welding equipment, and there may be other equipment in the vicinity that uses the same radio frequencies as those allocated for wireless networking.To operate reliably, wireless networking products have to take account of these factors.
Fortunately there are well-proven wireless DeviceNet and Ethernet products available that use techniques such as spread-spectrum transmission and diversity reception to give dependable results even in difficult electromagnetic environments, and also to minimise the risk of interaction with nearby systems. Omron ‘s WD30 wireless DeviceNet products, for example, allow up to 1,600 inputs and 1,600 outputs to be connected wirelessly to a DeviceNet network, leaving the user free to choose the most appropriate network topology to suit the needs of the application.
There are a few caveats when using wireless networking, perhaps the most important of which is response speed. Modern wireless networks are fast, but are not yet as fast as high-speed cabled networks. In addition, there is often some small but significant variation in the timing of signals transmitted wirelessly, particularly if high levels of interference are present.
This means that wireless connections are excellent for applications such as the transfer of routing data to a stacker truck, but less well suited for, say, stopping a drive instantly and accurately when the driven element reaches an index point.
While wireless DeviceNet and similar systems are undoubtedly an excellent option where it is necessary to replicate the operation of a conventional network or fieldbus installation without the use of wires, there are many other wireless possibilities in automation.
A simple Bluetooth connection to a PLC could, for instance, allow programming and monitoring access to the system without having to open the control cabinet door or possibly having to remove power to the system to do this.
It is, for example, no longer necessary to be on site to monitor and even control automation equipment. Modern programmable controllers can often be equipped with GSM/GPRS modems that enable them to communicate with mobile phones using ordinary SMS (text) messages.
Plants equipped with this facility can regularly report their status by sending text messages to one or more mobile phones, and can similarly send alarm messages by text when something goes wrong. The recipient, who only needs a standard mobile handset and to be within reach of the ordinary mobile phone network, can even send text messages back to the plant to initiate specific control functions.
While text messages are a popular form of remote monitoring facility, they are, of course, somewhat limited in the amount of information they can easily convey. For this reason, many automation systems can also generate and despatch emails that can be retrieved with any standard email client, or on a wireless portable device such as a Blackberry or iPhone.
It is the growing proliferation of Ethernet-enabled automation equipment, however, that is opening up the most exciting possibilities for remote and wireless monitoring. Many modern automation products have integrated web servers, making it easily possible to set up the installation so that each item of equipment can be directly interrogated and controlled using a standard web browser from any location where Internet access is available.
Using visualisation (HMI) and SCADA software, it is also possible to arrange for remote users anywhere in the world to look at and control the status of the plant as a whole, with fully transparent access to PLCs, drives, motion controllers and other essential elements. In effect, the remote user can have exactly the same access facilities that they would have if they were sitting next to the control panel on site.
Remote fault finding and maintenance then becomes a very real and cost-effective option, especially as the need for site visits is greatly reduced or even eliminated. This is particularly significant if the installation happens to be on the other side of the world from the company that’s responsible for maintaining it.
Naturally, remote monitoring can be carried out using a computer that has either a wired or wireless connection to the Internet, but a really interesting option becomes available if a wireless connection is made available on site. This is easily achieved by adding a WiFi router to an Ethernet-enabled controller. Rugged versions of wireless Ethernet access points and clients, such as Omron’s WE70 series, are perfect for the industrial environment.
With this arrangement, an engineer with a laptop computer can walk around the site and connect to the automation installation from virtually any location. The benefits for commissioning and fault-finding are enormous, especially on large plants where the control panel may be a considerable distance from the devices that it’s controlling.
The engineer can, for example, stand by an actuator anywhere on the plant and, using the laptop, request the control system to energise and de-energise the actuator so he or she can see immediately whether it is working correctly. Similarly, the control system can report instantly to the laptop whether or not it is receiving the correct signals from sensors and other input devices.
An arrangement of this type was recently implemented by a British company in a Canadian meat packing plant that made extensive use of Omron automation equipment. The site engineers reported that, in this large plant, the use of WiFi technology cut the time needed for commissioning from eight man weeks to just two.
Wireless technology in automation systems has a lot to offer. It can provide reliable data connections where no other method is possible, and it can provide remote access to installations anywhere in the world, via mobile phone, handheld device or computer. It can also be an invaluable tool for reducing the time needed for commissioning and fault finding.
Wireless systems may not yet have made the big impact in automation that might have been expected, but they’re certainly destined to be a formidable force for future innovation. Omron is currently demonstrating all of these connectivity methods, if you would like more information please call 01908 258258 and ask for Karl Walker.
- Karl Walker is marketing manager, automation products, at Omron Electronics