AVOIDING THOSE INSTALLATION "GOTCHAS" Ethernet is Ethernet and ever more shall be so - right? Not so, as many installers are discovering. As with any communications technology it"s vital to install correctly if the "gotchas" are to be avoided. But what are those "gotchas", and how does one avoid them? As ever, we turn to an expert for answers. Lots of those answers are plain commonsense, but many are more subtle and deserve close attention. by Sundar Balu There are several advantages to using Ethernet as a control network. Primary reasons are its low cost per unit bandwidth, lower cost of cabling and overall ability to handle high volumes of data.. There are essentially many similarities between Industrial Ethernet and Office Ethernet though Ethernet can be used for control in harsh environments. The major areas of focus here are reliability of connectors and physical media, ability to operate in harsh environments including temperature extremes, humidity etc. and varying operating procedures. Shock and Vibration The RJ45 connector by design is not intended for high vibrations. A rolling mill presents significant challenges for example. Fretting from small contact movements and oxidation will most certainly lead to contact failure. This leads to higher contact resistance and therefore to data signal attenuation and corruption of data packets. A truly sealed RJ45 connector such as RJLnxx? from Woodhead, with a clamping encapsulation is one alternative. This may be sufficient with control cabinets or in a sealed environment but for sustained exposure to pulling and flexing, a fully sealed overmoulded M12 connector (e.g. from Hirschmann, Lumberg"s etherMATE? or Turck specially designed for Industrial Ethernet) is preferred. The M12 in its design incorporates 8 contacts in a circular arrangement wired to specific pairs for optimal performance. Each contact is encapsulated in its own cavity within the moulding and has a minimum of 30microns of gold for reliable contact maintenance. Sealing Sealing is an important factor with connectors, cables and any field mounted device that is subjected to the harsh environment. Since COTS (commercially off-the-shelf) products provide no protection against dust, dirt, oil, water or other chemicals, the connector and its associated cabling must meet a minimum of IP67 protection. RJ45 connectors are not intended for harsh environments by the inherent design and selection of materials. A fully sealed M12 connector is not only designed for IP67 and IP68 environments, but has also stood the test of time. The factory floor has used M12 connectors for more than 2 decades for connecting sensors, switches and actuators in every imaginable environment. Temperature Temperature fluctuations can cause havoc in any control network and it is no different for Ethernet. COTS patch cords are not designed to withstand such conditions. A fully braided shielded PVC or PUR jacket offers protection to the internal conductors at extreme temperatures (-30 to 80C) and such cables are offered by vendors several including Commscope, InterlinkBT, Woodhead and Lumberg. Cracked cables or connectors can cause crosstalk and shorting. Higher temperatures lead to an increase in DC resistance of copper cables and thereby the attenuation of the cable. Switches or Hubs To optimize throughput on an Ethernet network requires restricted or negligible redundant traffic and no collisions. Hubs traditionally tend to degrade throughput. Switches are preferred, especially in where there could be many devices, spread out in a linear fashion, generating messages. Switches, by design, minimize traffic by allowing independent, virtual connections so that only devices that were switched receive their intended traffic to eliminate collision domains. A fully sealed IP67 switch from InterlinkBT or Woodhead are two options for field-installability. Bulkheads Bulkheads are recomme