Up Time Magazine- June/July 2008

vibration upload Sensors in a Corrosive Environment Don’t Let Your Data Be Compromised by Jack Peters I t was almost 20 years ago that we started to become interested in the vibration levels on industrial machinery and began to measure and monitor the frequency and amplitude for preventive and predictive maintenance. These early applications often included small accelerometers with miniature coaxial cables and microdot connectors that had been borrowed from the test and measurement labs. Although functional, they were never meant for the harsh environments found in and around industrial machinery. Cables and connectors were broken easily, difficult to repair, and always a constant source of noise and worry. Development of the modern industrial accelerometer provided a sensor packaged in a stainless steel case, included a ¼-28 threaded mounting hole, and a military specified connector known as the MIL C 5015. Finally, here was a connector that we could not only get our hands on, but one that we could also use with an industrial cable. This opened the door to a whole new world of cable and connector possibilities. Besides having a military standard, (after all, if it has been to war, it must be tough) components such as soldered contacts, twisted pair cables, braided stainless steel shields, protective jackets, epoxy filled and over molded connectors all became the latest rage. These components have been designed, tuned, and tweaked to perfection over the years. Today’s Teflon® jacketed cables with twisted shielded pair conductors and over molded connectors with stainless steel locking rings are so robust that even the largest and strongest Samsonite® Gorilla could use them to swing from tree to tree with no fear of ever falling. Although this would seem to be a job well done, being strong is not the only ingredient in being robust. There is no doubt that continuous online vibration monitoring and analysis is becoming standard in our industrial reliability programs. As we approach complete hands off environments for accelerometers, we are finding some difficult applications involving chemical compatibility on our industrial machines. It can be as simple as petroleum based oil or grease, or as complex as caustic soda (sodium hydroxide) often found in the bleaching process on the wet end of a white paper machine. Figure 1 – Accelerometer & Connector iron parts of the paper machine as a result of the continuous caustic soda environment in Figure 1.) Cables and connectors are combined into a cord set which transmits the vibration signal from the accelerometer to the point of data collection. Any breach in the cord set will cause loss of power, loss of vibration signal, noise in the vibration signal, or any combination of all three. Wet End Cables for Paper Mills Cables are made up of twisted conductors, a braided or foil shield, and usually a shield drain wire for grounding purposes. These internal parts are all enclosed by the outer cable jacket. Since the cable jacket is the only part of the cable exposed to the environment, we only need to have this jacket material chemically resistant to the caustic soda and chemically compatible with the environment of the paper machine. Common materials for cable jackets are Polyurethane, PVC, and Teflon®. In this caustic soda environment, Teflon® would provide a very robust outer jacket and also be extremely resistant to the caustic soda. Permanent accelerometers mounted in the wet end of a paper machine would be well served with Teflon jacketed cables as they provide the most robust Wet End Paper Machine Challenges Figure 1 provides a good view of the challenges faced for the cable and connector in the wet end of a paper machine. The wet caustic soda solution covers the seal tight boot portion of the connector and accelerometer in a hot steamy environment. In this adverse environment, the caustic soda solution is always in contact with the critical interface formed between the connector and accelerometer. (Note the extensive corrosion of the cast 62 june/july 2008

Table of Contents Feed for the Digital Edition of Up Time Magazine- June/July 2008

Up Time Magazine- June/July 2008 Contents Upfront Upclose: The True Cause of Most Machine Failures Information Technology: Finding Future Perfect Lubrication: Building an Oil Analysis Winner Maintenance Management: Hidden Ways to Increase Safety Infrared: Air Barriers Lower Energy Costs, Increase Profits Motor Testing: Efficient Motor Repair, Part Deux Precision Maintenance: Good Maintenance, Smart Maintenance Reliability: Common Errors in Root Cause Analysis Ultrasound: Avoid the Baghouse Blues Vibration: Don't Let Your Sensors Get Eaten Alive Upgrade: Lining It All Up

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