Festo adopts ABB’s wireless standard
13 January 2009
WISA-COM, the wireless communications standard from ABB, facilitates wear-free signal transmission to I/O modules. This will increase machine availability and reduce engineering and assembly costs. Festo has adopted this ABB protocol so that its sensor/actuator level now features one of the fastest and most reliable short-range wireless communications systems available.
Festo devices using WISA-COM
The system shows its strength in applications involving large numbers of sensors and actuators, concentrated in a small space and individually connected to a controller using cables and plugs. WISA-com allows hundreds of sensors to operate independently and communicate without interference in a volume of several cubic metres.
The large number of cable connections required for data transmission not only increases engineering and installation costs, but are also one of the most common causes of production downtime due to cable wear. The introduction of wireless sensor/actuator distributors means that signal cables in existing production systems, which are prone to malfunction, are now obsolete.
COMMUNICATION BETWEEN HUNDREDS OF DEVICES
The WISA-COM communications technology at machine level in factory automation is the only wireless technology that meets the strict requirements of industrial environments. WISA from ABB stands for Wireless Interface for Sensors and Actuators. The technology is extremely reliable and offers short response times. It facilitates communication between hundreds of devices in a system and offers reliable transmission even in areas where transmission is impaired due to obstacles or interference.
Wireless technology is particularly useful in special machine construction, where cables move and tools are frequently changed, as well as, for example, in robotic grippers, welding systems and assembly systems in the automotive industry.
Other industries are also benefiting from the new technology. In food production and packing machines, wireless data transmission clearly has the edge over wired solutions when it comes to stringent hygiene requirements or aggressive environments. It also reduces installation costs for complex and small-scale applications in the electronics industry.
The changeover to wireless communication requires a relatively small number of components and minimal changes to existing machine designs. The system is therefore suitable not only for new machines, but also for retrofitting in machines that are prone to frequent malfunction due to faulty I/O cables.
The input/output model with fieldbus plug, a pair of antennas with antenna cables as well as up to 13 sensor/actuator distributors are the ideal starter package for wireless communication.
The sensor/actuator distributors connect drives, valve terminals, position sensors or other binary sensors, contacts and switches with the machine controller. This facilitates flexible communication, which is independent of bus structures.
The system also functions as a gateway with Profibus DP and CANopen interfaces in the form of a radio base station for communication with the wireless I/O modules.
ABB’s WISA: AT A GLANCE
WISA = Wireless Interface to Sensors and Actuators
The communication operates in the 2.4 GHz band (ISM band). It uses frequency hopping, with a total of 79 frequencies.
One base station, or I/O module, supports 120 sensors or actuators in a range of 5m. The base station operates in full duplex, using five simultaneous RF communication channels. Up to three base stations can be located inside one 6 x 6 x 3 metre volume area.
The protocol allocates each sensor or actuator a specific time slot and frequency for its transmission. This, combined with frequency hopping, avoids collisions.
The most unusual feature of the system is the way the individual wireless nodes receive their power to operate. Power is supplied by electromagnetic coupling, like a giant transformer without the iron core. The nodes are surrounded by primary loops in a (typically maximum) 6m x 6m x3m box shape which produce a 120 kHz field. This induces current in small secondary coils in the sensors and actuators. The amount of power induced this way ranges from 10 to 100 mW.
ABB introduced its wireless system at Hannover Fair in 2002. To read Control Engineering Europe’s report written at that time, click here
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