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Ensuring network availability in an industrial environment

22 April 2014

Loredana Coscotin, product marketing manager for Industrial Cable EMEA at Belden, explains why industrial grade cables really can make a difference to the long-term performance and reliability of industrial networks.

Industrial plants rely heavily on their automation, instrumentation and control data communications to relay signals between devices, machinery and the control system to activate events on an exacting and pre-determined schedule, with little or no margin for error. Many industrial facilities are sizeable and their networking products must meet stringent industrial regulations and ratings. Many users also demand network availability of 99.999% uptime or better. A robust Industrial Ethernet infrastructure, consisting of environmentally hardened network cabling, connectivity, and active components is essential to long-term performance and reliability.

Maximum productivity with minimal downtime is a key goal, and 24/7 network performance and reliability are critical to achieving these goals. If a switch, connector or cabling system fails, the cost of parts replacement and repair represents just a fraction of the overall cost of any production downtime. Oil, gas and petrochemical plants, water and wastewater facilities, wind farms and mines are just a few examples where extreme environmental hazards can be detrimental to the performance and reliability of commercial-grade Ethernet cabling, connectivity and networking devices.

The cost of failure
If a cabling system component or Ethernet switch fails in a power generation facility, for example, the repair/labour costs alone could be 15-20 times the cost of the component itself. However, disruptions in the flow of information or control signals could lead to power outages. 

Downtime in an automotive assembly plant capable of producing one vehicle per minute would stand to lose profits of between 1,500 to 2,500 euro/minute for small car production, more for bigger vehicles.

The indirect costs of Ethernet system failure must take into account loss of productivity, delayed downstream processes, cost of system shut-down and start-up, and the potential loss of service to customers relying on a plant’s mission-critical output. 

Investing in a high-quality, rugged Ethernet infrastructure designed specifically for use in harsh environments is, therefore, a good business decision. Of course,despite every effort at the design stage and/or during installation, it is still possible that failures may occur in an Ethernet switch, in the connectors or the cabling. Whereas switches usually have backup configurations and connectors are usually easy to access, cables are always the most difficult to replace.

Solutions for harsh environments
The industrial environment places a great deal of stress on Ethernet cabling systems.

Networked communications systems in extreme environments need to be rugged and durable. Any physical deterioration or electrical failure in key data transmission components can lead to unreliable network performance and/or safety issues. So, using commercial off-the-shelf cabling products in the industrial landscape carries high risks for industrial and mission-critical applications.

The key differences between an industrial grade cable and a commercial grade one are the oil/chemicals/abrasion resistant outer jacket shield and the braid with a high level of stranding for specific trailing/torsion applications. For patch cords, there are various types of protection - IP20 overmolded protection, IP67 and IP68 dust penetration protection, IP67 temporary water submersion resistance, and IP68 – permanent water submersion resistance.

Belden conducted a series of tests to compare the physical and electrical performance of commercial off-the-shelf (COTS) cables with industrial cables. The results clearly indicate why a commercial grade cable is never suitable for the variety of extreme conditions that can apply in an industrial environment. The tests included:

Abrasion - Using a fixed drum covered with sandpaper, cables were stretched across a portion of their circumference, then moved back and forth cyclically for 25 cycle counts.The conductors of the commercial grade cables could be seen through breaks in the jacket, which would cause it to lose mechanical and electrical integrity.The conductor pairs of the armoured industrial cable were not compromised.

Cold bend - Conducted according to UL 444, samples of cables were left in a controlled temperature and humidity chamber. They remained there for one hour prior to testing. They were then tested (at -80°C, -60°C, and -40°C) by being partially wound around a 3in diameter horizontal mandrel with one end of the cable under tension from an aluminium weight. The commercial grade cables became brittle and showed visible cracks. The industrial grade high/low temp cable showed no visible damage.

Cold impact - Conducted according to UL 444, an aluminium weight was dropped down a hollow guide-tube to smash against a segment of the cable under test. The impact force delivered 24 in-lbs or 2.7 joules of impact energy. Each length of cable had been previously cooled. A total of ten samples were inspected at a series of increasingly lower temperatures to determine if the cable jackets’ integrity was damaged, which could allow ingress of chemicals and moisture and could potentially lead to a conductor-to-conductor short or catastrophic failure. The standard commercial grade jacketed cable failed at -20°C. The industrial grade cables, protected by high-low temperature jackets, did not crack until impacted at -70°C. Crushing - An Instron machine head brings a 2in by 2in (0.051m by 0.051m) plate down on a segment of cable to crush it – with failure defined as the point at which the cable would no longer reliably support Cat 5e performance. Each cable’s electrical characteristics were measured throughout the testing.At 400 lbs applied force, the commercial grade cable with PVC jacket failed – it was smashed flat and would not spring back to its original shape. The industrial grade, black-jacketed armoured cable had a failure value of 2,250 lbs– over a ton.

Cut-through - Based on CSA standard #22.2, a chisel-point mandrel on an Instron machine was lowered onto a segment of cable to test the cable’s susceptibility to a cut-through, leaving the conductor exposed. Several kinds of cable were sliced by the chisel to the point where a short circuit was sensed across the conductors, creating a potentially hazardous situation. The commercial grade cable shorted out at 92 lbs 41.73kg) of applied force. The armoured industrial cable took 346 lbs applied force to pierce the armour. However, the conductors did not short until a force of 1,048 lbs was applied. 

High temperature - Three spools of cable were suspended from a mandrel in a high-temperature oven. The cables were first tested at an ambient temperature of +20°C and were then tested again after being exposed to a high temperature of +60°C over time. The commercial grade cable functioned acceptably at +20°C but, over time, at +60°C, attenuation increased to where the cable would not support a run distance of 100m. The industrial grade cables, even after exposure to +60°C over time, continued to support the maximum run distance.

Oil resistance - Conducted according to UL 1277, lengths of cable were immersed in containers of oil, which in turn were immersed in a water bath that was placed in a chamber held at +125°C for 60 days. After the test period, cable segments were removed and their jackets evaluated for tensile and elongation properties. Exposure to oil and lubricants can make jacketing brittle and fragile, even at room temperature, resulting in loss of mechanical properties and reduced service life. The commercial grade cable showed signs of this type of deterioration. The industrial  jacket of the cable showed no signs of deterioration, because the materials and jacket thickness are rated forexposure to oil and other substances, even at elevated temperatures.

UV exposure - In this procedure-based ASTM G 154 test (Standard Practices for Operating Fluorescent LightApparatus for UV Exposure of Non-Metallic Materials), segments of various cables were affixed to panels that were mounted so that the cables directly faced a fluorescent light source whose output range was adjusted to match that of solar radiation levels. The cables were exposed to light for 720 hours then their jackets were visually checked for discolouration, as well as signs of degradation in tensile strength and elongation. The commercial grade cable was not sunlight resistant: jackets showed discolouration, a precursor to degradation of the jacket material. The industrial grade cables were rated to resist the effects of sunlight and other UV sources and showed no jacket damage.

Water immersion - At the beginning of this test, the electrical properties of the cables (primarily attenuation) were measured. The cables were then coiled into a dry container, and water was added to submerge them. The cables were tested intermittently over a six-month period. The commercial grade cable showed increased attenuation as soon as it was immersed in water and this continued to degrade over the half-year immersion.After six months of immersion, the industrial grade cable showed only a slight increase in attenuation – and the cable still exceeded the Cat 5e requirements.

Conclusion 
Rugged conditions call for the use of ruggedised cables. There is a significant difference between standard Ethernet cables and cables designed for industrial use. They are designed and built to withstand the hazards and risks they are exposed to day after day. Only Industrial Ethernet cable and connectivity solutions can really ensure the highest level of reliability, quality and performance at all times and for this reason Belden offers a range of DataTuff cables, specifically designed for manufacturing environments, with in-design, tested performance.


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