Proximitor® probe systems based on Eddy current technoloty have become common place in industrial plants these days. Everywhere a medium or high criticality machine is running, chances are that non-contacting eddy current systems are installed and are used for condition monitoring measurements and/or automatic machine trip or shutdown. More often than not, Bently Nevada Proximitor® probe system is used to protect and monitor these machines.
From the very first days that Don Bently invented and pioneered the use of the eddy current Proximitor® probe in the late 1960’s, quality, reliability and ease of use have been among the top priorities at Bently Nevada.
That tradition, rooted in our passion for customer service, is still alive and well today. And it is no more apparent than it is with our commitment to full interchangeability with our Proximity probe systems.
What does interchangeability mean?
With respect to Proximitor probe systems, interchangeability refers to the ability to interchange the probes, cables, and Proximitor sensors easily without the need for calibration or special tools.
For example, the most popular line of Bently Nevada proximity probe systems is the 3300XL 8mm system. Interchangeability means that with this system a plant can easily exchange 3300XL 8mm probes, cables, and Proximitors® without any significant change in output such as gap voltage or direct vibration.
Interchangeability is an important advantage. In the early days of eddy current system development, each probe, cable, and Proximitor® had to be tuned to match one another in a unique set. Anytime that a piece of the system needed to be replaced, a spare for that system that was an actual calibrated match was required. This meant that each vibration point on a machine potentially needed to have its own spare. On a typical 4-bearing machine this might mean the plant would need to stock or calibrate many different spares, in some cases, one for each eddy current driver, cable, and probe.
This was a very expensive, complex, time consuming, endeavor. Bently Nevada answered the need for a better way and pioneered the development of our gold standard technology that ensures complete interchangeability between the main Proximitor product families. As shown above, each family of Bently Nevada Proximitor has its own color-coding for easy identification.
Bently Nevada uses a metrology tracked gold standard system to ensure that a 3300XL probe purchased 18 years ago works correctly with a 3300XL Proximitor module you buy today and an extension cable you may buy 10 years from now. No one else in the industry besides Bently Nevada can claim this level of rock-solid performance AND interchangeability.
But what does it mean to me?
A simple example that plays itself out regularly at plants around the world regardless of industry is one in which either a cable or Proximitor needs to be replaced. It could be that an electrician accidentally stepped on a piece of conduit severing the probe cable. Or perhaps a Proximitor was damaged during installation or wiring or even a steam leak that “cooked” the sensor. Whatever the cause, no matter how bullet-proof the design of the Proximitor, it is a precision instrument and plants do need to replace them from time to time.
Without interchangeability, unless the plant actually stocked the exact calibrated match for the Proximitor or probe cable that was severed, there is essentially no way to replace the part and ensure that the reading is correct. The plant would need to shut down the machine, remove the machine covers, and access the bearings to be able to replace all three at once: probe, Proximitor, and cable, to ensure the reading is correct. In some industries that may not be an issue. In the critical process industries where equipment is expected to run for years without stopping, it is unacceptable.
With a fully interchangeable system like the Bently Nevada 3300XL, the plant simply replaces the damaged Proximitor or cable with an off-the-shelf spare part and continues to run, no calibration or special tools required and no need to disturb the probes installed deep within the machine. In fact, because of our gold standard and unmatched interchangeability, all of the machines at the plant can use exactly the same Proximitor drivers and cables and with a few different probe options, the plant’s entire needs can be covered by just a handful of spare parts shared amongst all the machines, which lowers maintenance costs and reduces the chances of system mismatch.
The “Frankenstein System”
Mixing and Matching Parts from Different Manufacturers
A typical Bently Nevada Proximitor, probe, and cable set is engineered to work together as a system. The discussion above gave us some background on what interchangeability is and why it is important to your operation. If you take the discussion a bit further and examine the mixing and matching of eddy current system parts from different manufacturers, you encounter the so-called “Frankenstein” system.
A Frankenstein system mixes and matches parts from different manufacturers that were never designed to work together. Whether out of a perceived cost savings, a simple lack of experience, or other factors, several plants have incorporated parts from different manufacturers to create these mixed-and-matched systems. At first, during installation they may appear to work correctly. However, several customers have experienced serious problems as a result of using the Frankenstein approach.
Case in point: One of our key customers operating a refinery in the Middle East recently called their local Bently Nevada Field Service office and complained that production was down because of intermittent machinery shutdowns of some of their critical turbomachinery. The Bently Nevada system was suspected of causing false trips and the customer was quite upset. Within hours a local Bently Nevada Field engineer from that region was on site to diagnose the problem.
Upon investigation it was discovered that all of the Bently Nevada Proximitors had been removed and replaced with something else. The Bently Nevada probes and cables were still in place but the Proximitor that was compatible with them using the Bently Nevada gold standard at the factory had been replaced with a competitor’s eddy current driver in the field with unknown electrical characteristics.
Upon discovering this, the refinery management launched an internal Root Cause Analysis (RCA) and determined that the mismatched eddy current driver was the source of the false trips. By changing from a Bently Nevada Gold Standard Proximitor with known characteristics and replacing it with a competitor’s unknown product, the plant inadvertently “changed” critical machinery set points without knowledge of the plant operations group! How were the setpoints effectively changed? Examine the results of the mixed system that was tested in the plots above. Clearly it can be seen with both the 5-meter system (left side plots) and the 9-meter system (right side plots), that the non-linear response and error of the mixed system can essentially “change” intended setpoints.
The shocking level of difference in the performance of the Bently Nevada system vs. the competitor’s product, and especially the difference in the mixed Eddy current system, is explained by the difficulty in manufacturing accurate, reliable Eddy current systems. These systems are relatively easy to manufacture and market, they are however very difficult to manufacture with repeatability and accuracy. This is what Bently Nevada has done so well for the last 50+ years and what separates us from our competition.
In addition to that, no manufacturer will warranty the mixing and matching of transducers and the consequences of that choice are completely in the hands of the end user and in some cases could lead not only to loss of production at the plant, but also unsafe conditions and risk to life and limb.
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