PQ Index – What does it mean?

Feb 24, 2014 | condition monitoring, oil analysis, Techenomics

Particle Quantification (PQ Index) is the measurement of total ferrous (Iron) particles present in the sample. PQ does not take into account size of particles. The ferrous is detected via magnetic fields and dependent on the type of laboratory equipment used, will determine how the measurement is taken. Regardless of this, the generated reading will report the total concentration of the magnetic particles in that sample.

What are the capabilities?

PQ Index can be used to measure ferrous wear metal particles in oil, grease and coolants. PQ analysers have no units and can be thought of as mass ferrous particles per mass of oil. Mass / Volume. PQ does not take into account particle size, we need to use the iron (Fe) readings of the elemental analysis to figure out what the concentration level is above 10 µm. Elemental Analysis cannot measure particles larger than 10 µm in size. This is where the PQ information can be very useful, especially in components that are starting to fatigue or have large internal wear starting to appear rapidly.

When should we be concerned?

Like all other analysis results reported by your laboratory, there are set limits or guidelines that are used to flag a sample as normal, monitor or abnormal. However, everyone makes mistakes and you should not reply on a smiley face or green arrow, tick or whatever your lab may use to flag a sample as normal, it is your responsibility to check the data and ensure nothing has been missed or overlooked.


When the PQ results indicate Low readings and the Fe level indicates Low readings – then the sample will contain minimal Fe particles most likely less than 10 µm and represent normal rubbing wear.

 When PQ results are Low and Fe is High, this most likely indicates particles are less than 10 µm and could be caused by acidic wear or larger amounts of rubbing wear.

 When PQ results are High and Fe is High, this most likely indicates majority of the particles are less than 10 µm and are from rubbing wear.

When PQ is High and Fe is Low, then this can become a concern because the majority of the wear is larger than 10 µm and will cause accelerated damage. The High readings of the PQ can be caused by many factors and will need further diagnoses or testing. Rapid High PQ readings on a trend scale can indicate a failure or potential failure. Never ignore High PQ readings and if unsure what it means, ask the laboratory to do a Ferrogram or Microscopic analysis on the sample. This can provide you with information on particle sizes, type of wear and particle identification all of which can be useful in helping diagnose the issue further.

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