The History of Oil Analysis, or

oil condition sensorThe emergence of onboard sensor technology and usage is clearly at hand and ever expanding. 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 us understand how this came about and, perhaps, where it might lead.

In the beginning: The first serious inspection efforts were made in laboratories Sending samples cross-country, and then waiting for a mailed report was exasperating to some. Regional laboratories began to thrive in the 80s and forward, and larger oil analysis firms opened branches in an effort to cover a wider geography via improved turnaround time. Facsimile machines helped in some instances, and the web, of course, would eventually become the de facto standard for returning reports. Nowadays, a mailed report, other than for confirmation purposes, is antiquated.

In the early 1960s came wear metals monitoring to complement lube quality and contamination monitoring. This approach was begun in earnest by U.S. commercial railroads in the late 1940s, but mainly confined to this singular application for over a decade. That was because the analyses were done by good old-fashioned bench testing by chemists, one metal at a time.

Then, Walter Baird invented the direct reading emission spectrometer, capable of analyzing for 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”, in effect.

Status quo, 1970

At this juncture (through the 1970s) the redefinition of oil analysis was: wear metals, viscosity, contamination and degradation testing of the lube. This suite of tests was reasonably complete and provided good information and value, but it lacked a major need, large (> 5 micrometers) particle inspections.

Large particle inspection

1980s technology brought about routine particle sizing and counting, directly addressing the need to detect and count particles from 5-100 micrometers. Particle counters don’t distinguish between particulate nature, simply sorting, sizing and counting; but parallel techniques like analytical ferrography (Vernon Westcott et al) allowed more comprehensive inspection, often including at least basic metallurgy. We could occasionally include more exotic testing, such as scanning electron microscopy, 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, dependent on the component and application.

Enter the Sensors

Time has seen systematic improvement and tremendous weight and size reductions in the instrumentation for analysis, and therein lays the path and connection to sensors. Most all used oil analysis is now done using computer-governed instrumentation. Sensors effectively represent miniaturization of bench-top instrumentation, but with little or no moving parts. As wet chemistry methods yielded to electro-mechanical, then computer-driven bench instrumentation, now that instrumentation is under siege from further miniaturization in the form of this thing called a ‘sensor’.

Like the first analytical instruments used for oil analysis, sensors initially demonstrated problems with sensitivity, accuracy, repeatability, dependability and so forth. 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, in most instances (as evaluated by several oil testing labs).


Today the most populous onboard sensor is still churning out dielectric strength readings (Fig. 1), but in far more sophisticated fashion, such that small differences can be observed and correlated to oil property changes, or ‘problems’. Something, e.g., additive depletion, water, fuel, metals, non-metallic contaminants, or a blend of such occurrences, has altered the dielectric constant of the oil, but that cannot be differentiated just from the sensor’s output. Clearly the next step would be to send a sample to a lab; but the sensor will have done its warning job of indicating significant change.

Oil monitoring sensors have further evolved to be more specific, addressing viscosity, water (Fig. 2), particle counting (Fig. 3), and ferrous debris (Fig. 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 swiftly but, rather, over decades from this juncture. 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 in life cycle cost assessments.

Sophisticated systems such as the composite sensor ‘suite’
(Fig. 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 such monitoring. In the case of large, expensive piston engines, it can be justifiable to monitor each cylinder for ferrous debris; thus, a 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 wherein the labs provide yet more sophisticated testing to supplement sensor observations.

Sorting things out

Once infrared analysis (FTIR) becomes sufficiently miniaturized and cost-effective (and that development is on the horizon), a host of oil property inspections will potentially become the domain of sensors. On that assumption, and with other developments now being perfected, we can expect the following substitutions for laboratory testing in the not too distant future:

•    Water (initially replacing cursory inspections, later, Karl Fischer)
•    Carbonaceous materials (soot)
•    Oxidation
•    Nitration
•    Sulfation
•    Contamination of synthetic oils with mineral oils
•    Certain types of additive depletion
•    Viscosity
•    Fuel dilution
•    Certain types of seal material
•    Ferrous debris (Particle Quantifier, Direct Reading Ferrography, etc.)
•    Particle count
•    ?

What might this leave for labs?

•    Some applications are not suitable for sensors (e.g., many 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

The prospect is not necessarily 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 that 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. There are a lot of people who use oil changes to ‘cure problems’, thus if the sensor result indicates a problem that is not immediately discernible, will a sample be pulled, or will the oil simply be changed, or will the result be ignored?

All three responses will co-exist in the maintenance world.

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