Wi-Fi for the Floor

You can fi nd it in your local Starbucks, at the airport, and now also in the plant. Gunter Baumann takes a look at Wi-Fi, industrial style.

Wireless networks are widely used in offi ce environments and are also moving into the fi eld of automation. However, classic wireless local area network (WLAN) technologies and products do not meet the requirements of industrial environments, such as cyclic data transmission in a grid of just a few milliseconds.

For this reason, components for industrial wireless local area network (IWLAN) need to be especially adapted for use in automation. Using these components the industrial user can apply wireless technologies to bring additional value, i.e. wireless data access giving them higher independence and flexibility on location and times.

When it comes to implementation in an industrial environment, the wireless network must satisfy concerns related to operating reliability, robust construction, and security.

Insist on reliability

In industrial applications, operating reliability is of particular importance. It demands the use of extremely reliable products providing mechanisms for real-time support (guaranteed transmission times) and deterministic transmission (predictable data traffi c). This means that devices such as programmable logic controllers (PLCs) can transfer their data reliably even in critical situations.

The wireless standards from the IEEE working group 802.11 provide only limited options, but are a good basis that can then be optimized for industrial application. Important factors related to reliability include provision of minimum data rate and a worstcase transmission time for selected clients (Quality of Service, QoS).

Adequate redundancy is also a key requirement, to ensure continued transmission in case of component failure. Redundancy can be provided by having two wireless cards to handle the same data stream and fast switchover (around 20 ms) if a problem should occur.

Operating reliability should also involve optimum planning and installation of the wireless network. Taking a measurement report of the fi eld strength values, for example, to ensure the availability of radio reception.

Hard for the floor

In addition to the reliable network connection, a robust construction and the choice of suitable connectors is an important requirement of the industrial customer. This means that metal housings need to be dust- and waterproof (IP65) so that devices can be set up at the ideal location (from a wireless transmission perspective), which means away from the switching cabinet.

Why? Well, the simplest location for installation is the switching cabinet nearby the PLC. But the cabinet functions like a Faraday cage, trapping radio waves. If an extra antenna is installed on the roof of the switching cabinet, the coaxial cable connecting the antenna and wireless module absorbs sensitive radio signals and valuable output power is lost along with a certain degree of reliability.

Industrial customers also attach great importance to expanded temperature range, resistance against condensation, vibration and shock and other features.

If additional thermal resistance is added to this defined protection against dust and water, the products can also be used outdoors. But an expanded temperature range is not only important for outdoor use; installation under the roof of the factory or in unheated logistics areas can lead to considerable thermal stress.

There is a similar problem relating to resistance to condensation. Changing temperatures even inside a building in conjunction with high humidity can cause condensation on and in the device.

Resistance to vibration and shock is necessary and must be proven in tests. This is particularly important because wireless is often used with moving devices. The mechanical load caused by turning or moving machine parts not only affects the device itself. It is also important that the cable connectors used are secured by screws or clamps to avoid the high costs that can result from a loose connector.

Naturally, industrial approvals such as EMC (electromagnetic compatibility), FM (Factory Mutual), UL (Underwriters Laboratories) and ATEX approvals for use in the petrochemicals industry and in hazardous areas are a matter of course. When used in paint shops, devices must be free of silicone. To avoid toxic vapors in the event of fi re, there must be no halogens either in the device or cable. If the products already have these properties and approvals, this is an important factor for the customer and helps to avoid additional costs.

Security questions

The question as to the degree of security often depends on the security policy of the company that prescribes clear rules. In this case, encryption of the data transmitted is important since the data traffic on a wireless link can be tracked using directional antennas. However, it is not enough simply to encrypt the data.

Even before any data traffic takes place, it is necessary to establish that the correct partners are taking part in the communication. The questions, “who are you?” and “what am I allowed to do?” need to be handled by suitable authentication and authorization protocols, respectively.

Whatever shape the security solution takes, it is important that the products used are standardized (use only mechanisms that are defined in the standard of the IEEE) and do not include proprietary procedures. A mainstream standard provides interoperability between different providers (protection for investment) and a high degree of data security.

Eye the ‘I’

Wireless applications can be found wherever mobility and flexibility are in demand. Simply substituting hard-wired cables does not normally deliver suffi cient benefi t except for installations that would involve considerable effort setting up cable ducts and racks.

Rather, in many applications, industrial wireless LAN makes it possible to optimize work processes and develop innovative solutions. Using mobile communication can for example simplify and speed up the commissioning phase and lead to considerable cost savings in logistics.

Service engineers

can monitor machine settings directly via their wireless service units and intervene immediately when problems occur. In applications requiring mobility and flexibility between automation devices like driverless transport systems, monorail systems, moving and rotating machines and a lot of other applications, drag chains, slip contacts and slip rings can be substituted by a wear-resistant wireless connection.

Siemens offers a range of industrial wireless LAN components specially built for industrial applications, which could only be satisfi ed with diffi culty, or not at all, using consumer devices.

The worldwide IEEE 802.11 radio standard has been supplemented with further features that have no detrimental effect on the compatibility, which are of major importance for use in industry and which justify the “I” in IWLAN.

Rugged design

Wireless Network at the Enterprise Level

Gunter Baumann is with Siemens Automation & Drives. Additional information provided by Jeremy Bryant of Siemens Energy & Automation.

Cables Make Good Antennas R-coax cables are radiating cables that function as special antennas for Siemens’ Scalance W WAPs (wireless access points) in applications needing complex radiocoverage patterns. The cables’ design creates a defined, cone-shaped radio frequency radiation pattern along the cable, and openings in the outer coaxial conductor permit penetration and emission of radio waves. This elongated radiation pattern is ideal for areas with complex radio coverage where “unlimited” mobility is not of decisive importance, but where a mechanically wear-free, low-maintenance solution is required to ensure reliable data transmission, such as conveyor systems, robots, rail-mounted vehicles, overhead conveyors, and AGV systems. The radiating cables are perfectly suitable for use in environments such as tunnels, channels and elevator shafts, and in any type of track vehicle. The cables were specially designed for the WiFi frequency bands around 2.4 GHz and 5 GHz. The Volkswagen plant in Emden, Germany, uses R-coax cable in critical radio system environments found in mobile screwing stations. Clients are able to communicate reliably with the plant’s control system and assembly line server. Lossy Cable RF Propogation