Particle quantification, or PQ Index, is the measurement of the total ferrous metal content of an oil. It is often the first method used to determine what other tests, or test programs, should be carried out.
The PQ Index ranges from 1 to 9999, with smaller numbers indicating a low concentration and larger numbers representing high metal content. To obtain this index, oil samples are subjected to a strong magnetic field which becomes distorted by the ferrous particles passing over it. The limits are set at low levels so that major problems can immediately be detected. The method is most useful to test differential, transmission and gearbox oils. The PQ Index picks up all sizes of ferrous particles, not just up to 8 microns.