Download: Accuracy.xlsm

The PCS Instruments HFRR (High Frequency Reciprocating Rig) is the industry standard instrument used for measuring diesel lubricity. The reproducibility is quoted at 102 microns wear scar for the standard HFRR 1.4 procedure. For the refinery blending to a maximum 460 microns specification, this introduces uncertainty that batches will be tested and proven on-grade. T

Measurement Accuracy is usually taken in to account by targeting a wear scar below the specification.The process accuracy in blending to a target can be estimated from the standard deviation of the batch release results and for a refinery in good control, this can be as high as 30 microns. Comparing this to the test method reproducibility of 102 micron (indicating a standard deviation of 36), and the test method is the major source of uncertainty.

A refinery can decrease the blending target to increase the certainty a referee laboratory will return a result on-grade or alternatively blend to a tighter target and expect a proportion of the blends to be re-tested as out of specification. The download link above, opens an Excel routine to assist with the calculation of the optimum target.