Ferrous wear debris analysis on machinery lubrication oils is a key step to monitor the condition of machineries to avoid any catastrophic failure. The analysis of abnormal ferrous content in oils is a proven method.
There are magnetometer based designs like the Midas instrument and the Kittiwake Analex PQ series or time resolved dielectric instruments such as the 5200 minilab. Some instruments like the Kittiwake Analex PQ series report ferrous content in “PQ” index, a dimensionless index. The scale range of the PQ instrument is from PQ=0 up to PQ=750. The PQ reading for normal wear is < 25.
The Spectro LaserNetFines Q230 Particle Counter
The Spectro LaserNetFines Q230 Particle Counter (Figure 1) determines ferrous content for the measurement and trending of abnormal wear with the help of its advanced, patent-pending magnetometer design. With the dual magnetometer design, the Wear Classifier can measure the total ferrous content in mg/ml, ferrous particle count and size distribution for Fe > 25, 38, 50 and 100µm.
Figure 1. The Spectro LaserNetFines Q230 Particle Counter
This article highlights the total ferrous measurement capability of the Ferrous Monitor instrument as well as its measurement accuracy and repeatability. The wear classifier capability or the ferrous particle count and size distribution capability of the Spectro LaserNetFines Q230 Particle Counter is not covered in this article.
Spectro Ferrous Monitor
The Ferrous Monitor in the Spectro LaserNetFines Q230 Particle Counter runs by detecting the variation in inductance of a coil caused by the introduction of ferrous material in small quantities into a sample cell within the coil (Figure 2). The two-channel instrument has a tiny coil for individual particle measurement and sizing and a larger coil to determine the total magnetic material content.
Figure 2. The Ferrous Monitor operates by sensing the change in inductance of a coil when a small amount of ferrous material is introduced into a sample cell inside the coil.
Experimental Procedure
This experiment evaluated the performance of a conventional magnetometer and the Q230 Ferrous Monitor against a gravimetric ferrous standard using a 50ppm solution of LNF-545, which is a Spectro Scientific gravimetric ferrous validation standard consisting of 76.2% ferrous in a 75 cSt matrix oil.
From the ferrous validation standard, six samples were taken and analyzed on both the LNF Q230 and the conventional magnetometer. After each measurement, the magnetometer was zeroed through measurement of a non ferrous sample before the next validation sample measurement. The LNF was run normally and flushed after each measurement using Electron 22.
Experimental Results
The experimental results for the six samples as well as the 50ppm reference line are presented in Figure 3.
Figure 3. Experimental results
The following table summarizes the results, accuracy and precision of the LNF Q230 and the conventional magnetometer:
| |
Q230 |
MIDAS |
| Sample 1 |
46.38 |
34 |
| Sample 2 |
41.62 |
38 |
| Sample 3 |
50.02 |
40 |
| Sample 4 |
47.22 |
34 |
| Sample 5 |
51.55 |
39 |
| Sample 6 |
52.77 |
30 |
| Std Dev |
4.07 |
3.82 |
| Avg |
48.26 |
35.83 |
| RSD% |
8.44 |
10.65 |
| Accuracy (average) |
3% |
28% |
Conclusion
The Q230 provides more accurate and repeatable ferrous measurement when compared to the conventional magnetometer, proving its suitability for abnormal wear measurement and trending to in order to monitor the condition of machineries.
The accuracy of the Ferrous Monitor in the Q230 is ± 3%, a much better value than ± 28% accuracy of the conventional magnetometer. In addition, the Q230 shows superior repeatability with 21% less RSD% (Relative Standard Deviation) when compared to the conventional magnetometer.
This information has been sourced, reviewed and adapted from materials provided by AMETEK Spectro Scientific.
For more information on this source, please visit AMETEK Spectro Scientific.