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Onboard sensor technology and its usage is expanding every day. These types of sensors represent a dynamic, long-term paradigm shift in the way oil is and will be analyzed. Tracing the history of oil analysis will help explain how this came about and, perhaps, where it might lead.
In the Beginning
Wear metals monitoring came about in the 1960s to complement lube quality and contamination monitoring. This approach was begun in earnest by U.S. commercial railroads in the late 1940s, but was mainly confined to this singular application for more than a decade. This was because analyses were performed by old-fashioned bench testing by chemists, one metal at a time.
Then, Walter Baird invented the direct reading emission spectrometer, capable of analyzing dozens of elements in one pass, and requiring no special talent in chemistry to operate. This was the major paradigm shift in oil analysis, which had suddenly become "machine analysis."
Status Quo, 1970
Large Particle Inspection
The technology of the 1980s brought about routine particle sizing and counting, directly addressing the need to detect and count particles from five to 100 micrometers. Particle counters don't distinguish between particulate nature, simply sorting, sizing and counting; but parallel techniques like analytical ferrography allowed more comprehensive inspection, often including at least basic metallurgy. More exotic testing such as scanning electron microscopy could occasionally be included, but today the modern oil analysis suite is rather comprehensive and includes wear metals, contamination and degradation tests, general particulate analysis and wear particulate analysis.
Enter the Sensors
Like the first analytical instruments used for oil analysis, sensors initially exhibited problems with sensitivity, accuracy, repeatability and dependability. The first popular sensor was a small, portable dielectric constant device, roughly modeled after larger units used in transformer oil testing. Several manufacturers ventured into this market with handheld devices, but none delivered a product that was discriminating enough to be highly useful (as evaluated by several oil testing labs).
Oil monitoring sensors have further evolved to be more specific, addressing viscosity, water (Figure 2), particle counting (Figure 3) and ferrous debris (Figure 4), among other more singular properties. It is perhaps a matter of time until complex differentiation of particles as to metallurgy, shape and quantity is feasible via onboard sensor, as technology continues to drive capabilities up and costs down. If and when this occurs, are used oil analysis laboratories out of business? Perhaps, but such an occurrence is not likely to happen any time soon but, rather, over decades. First there is the matter of technology development (the R&D), then the cost to bring products to the marketplace. There will also be the issue of retrofitting, which may not prove economical for older equipment in life cycle cost assessments.
Sophisticated systems such as the composite sensor suite (Figure 5) are cost-justifiable for a few component types. Large installations, such as ocean-going vessel engines, or gas transmission engines/compressors are typical candidates for this type of monitoring. In the case of large, expensive piston engines, it may be justifiable to monitor each cylinder for ferrous debris; thus, a two-cycle 10-cylinder engine would utilize 10 ferrous debris monitors.
It seems reasonable to expect that sensor development and proliferation will replace numbers of the tests now performed in laboratories, causing yet another paradigm shift in which the labs provide more sophisticated testing to supplement sensor observations.
The Future (Sorting Things Out)
Water (initially replacing cursory inspections, later, Karl Fischer)
Carbonaceous materials (soot)
Contamination of synthetic oils with mineral oils
Certain types of additive depletion
Certain types of seal material
Ferrous debris (particle quantifier, direct reading ferrography, etc.)
Some applications are not suitable for sensors (systems without circulating pumps such as gear boxes may not apply).
Spectrometric metals - a tough challenge for sensors near-term.
Microscopy (analytical ferrography, SEM) - competing, however, with onsite filter patch inspections.
New discoveries for insight into machinery via oil analysis, something laboratories and instrument manufacturers have been doing all along.
This prospect is not immediately bleak for labs because the evolution (paradigm shift) figures to be a plodding process by today's standards. Still, some unexpected development may accelerate this shift faster than anticipated, and the above scenario could transpire in a matter of a few years.
Leaving the above scenario to its course, how might sensors alter sampling habits in the meantime, and over the course of this evolution? This is a far more interesting question and proposition, because human nature will play a major role in its answer. Many people use oil changes to cure problems, thus if the sensor result indicates a problem that is not immediately discernible, will a sample be pulled, will the oil simply be changed, or will the result be ignored?
All three responses will co-exist in the maintenance world.