Wireless Switch

Overview of the wireless switch

Wireless switches grew out of the telecommunications industry and employ a transceiver to transmit and receive radio signals.

This technology is increasingly being deployed in industrial applications, usually in the form of new-generation limit switches on machinery. Equipment developers have been quick to use it by devising an expanded range of applications for wireless switches. They have enabled designers to position switches in locations which, with the older wired technology, would have been impossible, largely because obstacles between the equipment and the control console would have prevented adequate wire routing. Wireless switches have also proved exceptionally flexible with regard to modifications to the installation, because their position can be altered with relative ease.

Basic wired components in industrial monitoring can now be converted to wireless switches at relatively low cost and very speedily.

The IEEE 802.15.4 protocol that emerged with the advent of wireless technology robustly delimits a wireless Personal Area Network (PAN) specifically capable of targeting the kind of low bandwidth, low-power signals emitted by many switches used in industrial settings for control and monitoring purposes. IEEE 802.15.4 transceivers have over the last few years increasingly been deployed in wireless switch technology to transmit information to a receiver from a remotely located switch.
The receiver then converts the signals it collects into something compatible with standard controllers.

 

History of wireless technology

After some initial setbacks, enormous advances have been made in wireless technology over the last ten years by the telecommunications industry. As they overcame the early technical difficulties, wireless design innovators started to develop the technologies that could extend beyond telecommunications to other applications.

Wired limit switches, for example, have been in use for decades, typically to provide information on positioning of heavy industrial machinery. They are used in a vast range of different equipment, from storage tanks to automatic gates, lifts to crane booms, providing operatives with vital information about the position, presence or absence of moving objects.

In recent years, however, wired limit switches are being increasingly replaced by wireless switches. When wired switches are replaced with wireless alternatives, the expense of wiring is immediately removed and, because there are no cumbersome wire routing problems to circumnavigate, wireless switches can be positioned in locations their wired predecessors could never have been placed. The wireless switch also removes the danger of trip hazards that wired alternatives frequently pose.

 

Technical aspects

Mechanical limit switches can be integrated with appropriate wireless transceivers, converting them into wireless switches capable of transmitting movement changes to a monitoring receiver. The latter will often collect signals from several switches configured, for example, in a basic 'star linkup', which enables every switch on the network to communicate with a single receiver. The system works by every switch possessing a network identification number of its own and each network having the same. It is this element that ensures that "cross-talk” from other networks and switches is eliminated and that the signalling and information integrity between them remains private and secure. Because in the star configuration switches are linked independently and directly to the receiver, no signalling takes place between the switches themselves. This ensures that one switch is unable to compromise the integrity of another.

For optimum levels of performance, transceivers should be placed in areas where there is a largely obstruction-free space between the monitor and the switch. Uncluttered outdoor spaces are ideal, as are unchambered, open indoor areas. It is worth noting that engineers should not expect significant drop outs from minor obstacles, rain, or snowfall as these should not interfere with communications thanks to a 35-dB link margin. The signal is also capable of passing through intervening walls - although this does depend upon the wall’s composition.

Another key feature of the 802.15.4 is the size of the operating range. These are usually extensive and measure in excess of 304 metres. Engineers should be aware however, that some ambient weather conditions will cause a drop in the effective range of the device. Extreme weather – including heavy rain or snow if located outdoors – can see the 802.15.4 signal drop quite substantially to 23 metres. Indoor environments with a heavy suffusion of the surrounding air with particles will produce
similar effects.

In most cases, wireless switches consume so little power that they can be operated with industry standard batteries. They do not rely on expensive, unreliable and situation-dependent energy scavenging, and effectively multiply installation options to an almost limitless extent. Properly designed wireless switches, moreover, will not require battery re-charge or replacement for several years.

The other half of the wireless switch installation, of course, is the receiver/monitor. This can be exceptionally versatile, capable of supporting a single switch or several (some can support as many as 14 different remote wireless switches). The controller will indicate the activation status of each of the switches on a network, as well as other information such as their battery levels and signal strengths.

 

Where the wireless switch is used in manufacturing

As noted earlier, wireless switches can be deployed across an extremely varied range of industrial applications. The construction industry is one such area that has taken the opportunity to explore some of the potential of wireless technology. Cranes for example - where the wireless switch will usually be located at the end of the boom – have seen an improvement in safety and accuracy as vital positioning information (such as when the cable jib is nearing the end of the boom) has meant that operators have a reliable guide to how far they can safely spool the cable.

Because they require no intricate routing, wireless switches can function as limit switches in locations where it would have been impossible to install a wired alternative. Equally, they can be positioned everywhere where wired limit switches have traditionally been used, including on gates and canal locks where they will transmit to the control system the gate’s position very reliably and accurately.

Like their wired predecessors, wireless switch enclosures can support a variety of head and lever options to fulfil a diverse range of actuation and position requirements. They can be designed with top plunger, top roller, side roller and top roller lever operators and can be installed on automatic garage doors to shut the motor off when the door has reached its fully lowered and fully raised positions, as well as on equipment such as industrial lathes and storage tanks.

 

How the wireless switch differs from other switches

When wired limit switches are converted to wireless switches, the range of options for their installation in hitherto “impossible” locations multiplies, because expensive, cumbersome and potentially hazardous wire routing is completely obviated. Unlike their wired predecessors, wireless switches are now providing those who adopt them with clear advantages in the design of new generation transportation and industrial equipment.