17 April 2018 | Oil, fuel & coolant analysis | E-news, Technical
PQI is similar to Direct Reading Ferrography in application. The advantage PQI has over Direct Reading Ferrography is that test results can be provided quicker to the customer at a reduced cost.
Reported test results are not an absolute quantity calculation. Instead results reported are a relative concentration index. A higher rate of ferrous wear will report an upswing in the trended index. Also equipment with a high concentration of iron, such as gear sets, will report higher trended historical data.
PQI data can also determine overall size concentration of iron particles. Low iron test results and a high PQI would indicate overall particles are large (>20 micron). High iron test results and a low PQI would indicate overall particles are small (<10 micron). If iron and PQI results are at relatively the same concentration then it usually indicates overall size range of particles is small. Seeing a test report with low iron test results and a high PQI, indicating overall large particles, can also predict accelerated wear or impending catastrophic wear, especially if there is a sudden upswing in the trend analysis.
David Doyle, CLS, OMA I, OMA II