Which industrial wireless Ethernet is right?

IT in Manufacturing

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December 2012 IT in Manufacturing

There are several factors which should be considered when choosing which industrial wireless Ethernet system is right for an application. Country specific regulatory requirements are foremost, but apart from regulatory rules, different frequencies and standards have their pros and cons which need to weighed up. Presented here are some of the considerations when making a decision:

* RF regulatory requirements – most wireless Ethernet equipment will fall within the ISM (licence-free) bands, but users need to be aware of the restrictions. Your radio vendor should be in possession of a valid radio dealer’s licence as well as certified TA (type approval) for all radio hardware being sold. This includes industrial wireless Ethernet equipment. It is important to deal with a vendor company that is familiar with these RF regulations in order to ensure compliance for the system.

* Reliable communications distance – radio communications range is determined by a few key factors namely the total transmit power (government regulated), the receiving modules receiver sensitivity and the losses in-between, including cables, connectors and the radio path itself. It is possible to calculate the performance of an Ethernet radio link under ideal conditions, but this requires certain assumptions. The most reliable way is to conduct a physical site test if this is possible. Keep in mind that wireless Ethernet systems require a minimum signal level in order to yield a certain data throughput.

* Frequency and terrain – the radio path may be described as either obstructed or line-of-sight. The radiated radio signals form an elliptical path known as a Fresnel zone. It is the level of obstruction relative to the frequency and its Fresnel zone that determines the success level of communications. Higher frequencies such as 2,4 and 5 GHz have smaller wavelengths (and Fresnel zones) and can be susceptible to obstructed paths. For these two frequency bands, it is always best to have line-of-sight, especially for very long distances. Lower frequency systems (400 MHz and 800 MHz) are more forgiving, but trade-off data throughput for the benefit.

* Data throughput – when it comes to data throughput faster is not necessarily better. This is especially true for systems where the volume and regularity of data is low (eg, monitoring a tank level for pump control). Most PLCs have Ethernet interfaces, it is important to understand the (true) wired Ethernet speed requirements when choosing a radio-based system to replace the cable. Because the licence-free band is open, the system is susceptible to interference from other wireless Ethernet systems, which could affect latencies.

For more information contact Willem Krige, Tabateq, +27 (0)21 762 8995, [email protected], www.tabateq.com

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Which industrial wireless Ethernet is right?

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