The newest generation of wireless LAN (WLAN) not only brings higher data speeds, but also provides an innovative wireless interface that has been specially designed for use in automation. Here’s the story behind it!
When setting up a reliable wireless network, there is plenty of hardware around that is adequately vibration-resistant, waterproof, well-suited to long-term use, and which fulfills all the relevant standards. But, despite all this, WLANs still don’t always operate as well as they should.
Figure 1: A transmission mast equipped with different wireless technologies
One example of this was an installation at the Hamburg docks, intended for shore-to-shore and ship-to-shore wireless communications. Engineers were able to choose installation locations where there was obstruction-free line of sight between the antennas and the access points, there was no great distance between the transmitter and the receiver, and signals received in tests appeared strong enough to provide the desired bandwidth. But in use, data transmission was of poor quality and subject to frequent interruptions, with many data packets being lost or corrupted. Ships that wanted to set up temporary connections were particularly affected.
So a complete and expensive frequency analysis was carried out. WLAN is restricted to a maximum output power of 100 mW in the 2.4 GHz band, and to a maximum of 1000 mW in the 5 GHz band. This means its transmissions are weak compared with the other wireless technologies in the immediate vicinity. Because WLAN antennas receive all types of electromagnetic waves, the WLAN devices have to try to filter out the right signal from a jumble of different ones. Unfortunately, the frequency filter in the chip set isn’t particularly powerful.
Figure 2: Frequency analysis of the Hamburg docks
The problem was alleviated by installing an additional bandpass filter between access point and antenna, which prevented the interference picked up from neighboring frequencies from being passed on to the WLAN receiver. This considerably reduced the noise level and raised the packet receive rate to acceptable levels.
Figure 3: Output power and distribution of wireless systems across the frequency band
Another situation where unexpected problems were encountered was in an open-cast mine. WLAN devices had been installed to create a mobile network connection along the conveyor belts. Devices gradually lost transmit power and were finally unable to ensure the required data transmission level. It turned out that there had been regular electrostatic discharges above the open-cast mine caused by friction between the air masses. The WLAN antennas had been receiving and passing these discharges on. Because they were below the trip voltage, they were able to get past the lightning protection.
In both situations, the problems were solved by installing supplementary components between the WLAN devices. In the first case, this was a bandpass filter, and in the second case it was an advanced type of surge protection that works even at low voltages and currents. These both added substantially to the installation cost and to the space requirement. However, in many industrial scenarios, space is at a premium—in trains, for example–and multiple antennas may require multiple surge protectors and/or bandpass filters.
Figure 4: WLAN signal after the bandpass filter
This is why Hirschmann has developed a WLAN interface that fulfills all the requirements of industrial applications such as those described above. Designers have managed to integrate the surge protection and band filter components within the access point itself.
Each module now represents a wireless interface, and up to three of these can be installed in one access point. Tests have shown that the integrated surge protection can withstand discharges of up to 25 kV. The second integrated component, the bandpass filter, operates in either the 2.4 GHz or 5 GHz band and eliminates noise interference from the WLAN network.
Figure 5: The new OpenBAT range of WLAN devices from Hirschmann contains patented wireless modules with integrated bandpass filters and ESD protection, all as standard
The new, patented OpenBAT platform from Hirschmann is the latest generation of WLAN devices. It represents a new stage of WLAN development and permits data speeds up to 50% higher than in previous device generations. In addition, this platform allows customers to cater for all their requirements from a vast range of interfaces, power supplies, housing types and special certifications.
WLAN networks can be configured with OpenBAT devices as standalone access points or, alternatively, managed using a central BAT controller. The new OpenBAT platform allows WLAN solutions to be implemented in areas where this was not previously possible. Areas of application now include plant and process automation, energy transmission and distribution, mining, and power generation from renewable energy sources. Furthermore, customers can save money by choosing the product variant that has just the features they really need.
The patented WLAN wireless module is not only equipped with integrated bandpass filter and ESD protection, it also features ultra-low power consumption and an extremely wide operating temperature range. Plus, it has exceptionally robust antenna connectors and is therefore particularly resistant to vibrations.
From now on, it is possible to set up stable and reliable wireless connections even in the most difficult environments!