Accuracy, Precision, Detection Limits
Accuracy of this type of sensors employing indirect measurement usually depends on the accuracy of
the reference method used for calibration, as well as stability of the measured sample from the stand
point of the analyte nature and content. However, the precision expressed as standard deviation of the
series of measurements describes both stability of the matrix and the instrument optical and electrical
system. With regular update of the output every second, the FP360sc demonstrated very good precision
in all the different measurement conditions and samples. The Limit of Detection (LOD) is a cornerstone
characteristic of a measurement system. In the case of the FP360sc, it was confirmed during the testing
that the LOD was below ~30 ppb of average oil product concentration. This corresponds to the specified
value of 1.2 ppb of PAH model used to derive the specification. It is very important to understand that
the value of 36 ppb oil concentration (specified LOD) was derived as an average and it can vary from low
ppb to higher values for real petroleum products based on their nature and concentration of PAH-type
compounds.
Range
The range of measured oil concentrations is based on the LOD, as explained above, and on the total
content of PAH in the oil products. The higher is the PAH content of the measured oil, the lower its limit
of detection (closer to the specified for PAH = 1.2 ppb). On the other hand, the lower the PAH
concentration in the measured oil, the higher the top measurement range is. These two characteristics
are crucial to understanding the suitability of the FP360sc to various applications encompassing
environmental (low range), municipal and industrial waste water monitoring, and oil/water separation
applications (high range).
Vadim B. Malkov, Ph.D.
Product Applications Manager
Process Instrumentation
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