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Industrial Wireless Ethernet
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Ethernet Modem Series
Elpro's wireless Ethernet modems connect via RJ45 providing transparent Ethernet communications between LAN's and/or field devices such as PLC's. These products offer both broadcast (simultaneous transmission and receipt to all nodes) and controlled communication modes (specific addressing and communicating to a node). Additional I/O capability can be readily incorporated by combining Elpro's 115S serial expansion modules to the Elpro Ethernet modem range.
The Ethernet range is capable of being programmed to act in Router/Bridge, AP/Client and serial server (RS232/485) modes with repeatability between 2.4/5GHz units via AP - AP (WDS mesh) capability. Security measures include MAC address and IP filtering and encryption to WPA2-802.11i military standards.
Understanding Practical Ethernet Commissioning
Aspects to consider when choosing which type of industrial wireless Ethernet to commission for your application
Which Wireless Ethernet Is Right For My Application?
There are several factors which should be considered when choosing which industrial wireless Ethernet is right for your application: of course country specific regulatory requirements are foremost.
Reliable Communications Distance
Reliable wireless Ethernet communications is fundamentally determined by a few key factors: the amount of Radio Frequency (RF) power emitted from the antenna (government regulated), the lowest level that the receiving module can reliably demodulate (ie receiver sensitivity) and the frequency waveform properties relative to the terrain over the distance required of the application.
Alternative products RF power and receiver sensitivity are fixed in manufacturing. When choosing a wireless product, care should be taken to compare the amount of RF power and the receiver sensitivity of alternate product options.
Frequency and Terrain
Radio signals are transmitted between the sending and receiving units. The radiated radio signals form an elliptical path of concentric circles known as a Fresnel zone. The radio path may be described as either obstructed or line of sight.
It is the level of obstruction relative to the frequency waveform and its Fresnel zone that determines the success level of communications. Higher frequencies such as 2.4 and 5GHz have smaller waveforms and can be susceptible to obstructed paths. 2.4GHz waveforms are relatively less susceptible due their bigger size but may suffer from congestion in the 2.4GHz spectrum.
The image to the top right demonstrates the Fresnel zone between two antennas over the distance required of the application. It is the amount of obstruction relative to the waveform Fresnel zone (and other factors) that determines success.
What causes congestion in the 2.4GHz band?
The IEEE 802.11 standard specifies the number/separation of channels in the 2.4 and 5 GHz spectrums. Country regulations dependent, the 2.4 GHz 802.11b/g IEEE standard uses up to 14 channels with only three non-overlapping channels (1, 6, 11).
With the overhead and communication frames of the 802.11 standard, shared channels can create an RF environment which can be heavily congested when multiple 2.4 GHz systems are within hearing/receiving range of each other.
Image shows 2.4 GHz shared channels; 1, 6 and 11 are non-overlapping.
The 802.11 5GHz Spectrum
The IEEE 802.11a (5 GHz) standard specifies, country regulation dependent, up to 24 non-overlapping channels. There also can be additional radiated power (ie EIRP) from the antenna allowing greater distance Ethernet communications.
Image shows 5 GHz spectrum with up to 24 non-overlapping channels.
Data Rate Throughput and Modulation
The IEEE 802.11 standard has ratified four modulation techniques since 2007 including: 802.11 a, b, g and n.
| Standard | Frequency | Data Rate |
802.11b | 2.4 GHz | 1-11 Mbps |
| 802.11g | 2.4 GHz | 86-54 Mbps |
| 802.11a | 5.0 GHz | 6-54 Mbps |
| 802.11n | 2.4 GHz | 6-200+ Mbps |
The respective modulation techniques range from single to multi-spatial dimensional transmissions; particularly 802.11n which requires multiple antenna arrays. The 802.11 a, g standards allow for data throughputs to 108Mbps in turbo mode. However these standards do not use the antenna arrays of 802.11 n and are therefore more readily commissioned over distance applications.
In summary the above considerations should be taken into account when deploying industrial wireless Ethernet in your application.
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