Spectro Scientific

MicroLab Series – Fully Automated Oil Analyzer

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Courtesy of Spectro Scientific

Introduction
The MicroLab 1 is a fully automated, bench-top analyzer specifically designed for the analysis of oil samples to provide comprehensive analytical and diagnostic results of engine, generator, gearbox, hydraulics, power steering and transmission fluids. The MicroLab was developed to bring oil analysis capability to any company that maintains equipment and seeks to improve their overall equipment readiness. Companies can send oil samples out to a traditional lab but that process can take days or weeks for results. The MicroLab provides results in less than 15 minutes allowing the mechanic to take immediate maintenance action. The MicroLab is well suited for over-the-road and off-road vehicles, generators and other reciprocating machinery.

The MicroLab is the ideal trending tool to allow companies to identify mechanical problems before they become catastrophic equipment failures. The ability to track the serviceable life of the oil to know when they can safely extend the oil drain interval helps save money on oil consumption, oil disposal and labor costs associated with unnecessary oil drains.

The MicroLab is the first compact analyzer that combines multiple measurement modules, automated fluidics and interactive software to provide non-laboratory users the capability to obtain analytical results along with diagnostic interpretation. The MicroLab's innovative design and methods hold multiple patents and the analyzer complies with the ASTM standard for a Multi-Functional Oil Analysis Instrument, ASTM D7417. It combines four separate test components in an all-in-one, fully automated analyzer. The MicroLab includes an infrared spectrometer (IR) for six parameters for oil chemistry and contamination, an optical emission spectrometer (OESI to report up to 20 elements for wear metals, contaminates and oil additives, a dual temperature viscometer (DTV) to report viscosity at 40° and 100°C along with viscosity index, and an optional particle counter.

This paper serves as a guide to the technology and design considerations for the MicroLab and includes what to expect when comparing it to laboratory methods and results.

Elemental Analysis

Elemental analysis is the backbone of any oil analysis program and is designed for detection of wear metals and other impurities as well as oil additive levels to provide information on equipment condition and oil health. MicroLab 30 analyzes 10 basic metals: aluminum, chromium, copper, iron, lead, molybdenum, potassium, silicon, sodium, and tin. It is upgradable to include all 20 elements. MicroLab 40 analyzes 20 elements including the basic metals and the extended metals: barium, boron, calcium, magnesium, manganese, nickel, phosphorous, titanium, vanadium, and zinc.

Principle of Operation
The MicroLab employs Optical Emission Spectroscopy (OES) to quantify elements from mechanical wear, oil additives or sources of contamination. OES relies on the fact that every element has a unique atomic structure. When an atom is excited with enough energy it will emit light of discrete wavelengths (or colors) based on its atomic structure. Since no two elements share the same pattern of emitted wavelengths, the emission spectrum is a fingerprint that can be used to identify the elements that are present in a sample as shown in figure 1. Also, the intensity of the emitted light can be correlated to the concentration of that element in a sample.

An optical emission spectrometer consists of three parts: (1) the excitation source, (2} the optical system, and (3) the readout system. The two most popular methods of elemental analysis for oil analysis available on the market differ primarily in the excitation source of the sample: Inductively Coupled Plasma Spectroscopy (ICP) and Arc/ Spark/Rotating Disk Electrode Spectroscopy.

In the MicroLab OES, the spark module consists of a spark stand, two electrodes and a high voltage power source. As shown in Figure 2, high voltage from a computer-controlled pulsed power source is applied to the upper and lower electrodes of the spark stand to generate electrical spark and create plasma. The oil sample is pushed through the hole to the top of the lower electrode where it is heated, vaporized and atomized. The atomized elements are subsequently excited by their collision with the high energy particles in the plasma flume. Some atomized elements are ionized and the formed ions are excited. ground states, they emit light which bears the signature of the emitting element. The emitted light is collected with the lens and delivered with an optical fiber to the optical spectrometer, and the data of emission spectrum is collected. The optical spectrometer collects the spectrum in the ultraviolet (UV) and the visible (Vis) light region.

The collected sample emission spectrum is analyzed with a sophisticated data analysis procedure to identify and quantify the elements. Figure 3 below shows a representative emission spectrum (in red) of a customer used oil sample.When these excited atomic or ionic elements return to their and for comparison an emission spectrum of while mineral oil is shown which contains no metal element at all. The emission lines (or peaks) for iron (Fe), Silicon (Si), and copper (Cu) are identified based on their wavelengths. By measuring the peak area of each element and comparing to the peak area of the standard samples measured at the time of instrument calibration during production, the concentration (in ppm) of the element is then determined.

Several parameters of the OES system, such as spark frequency, voltage, gap between the electrodes, and oil sample flow rate, can affect the plasma characters and consequently influence the accuracy of the concentration measurements for the sample. These parameters are optimized during production, and then the OES is calibrated with a set of standard samples with known concentrations of the elements. The calibration coefficients for each of the elements are stored in the computer and used later to calculate the element concentrations for unknown customer samples.

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