RE: ACT VS12-04 Performance Verification Statement
July 25, 2013
Comments on ACT Assessment of Hach FP360sc Fluorometer
The Hach-Lange FP360sc Oil-In-Water sensors (PAH, Crude Oil and Refined Fuels) were evaluated by ACT
for response time, linearity, accuracy/precision, and reliability. The testing, at all test sites and modes,
was conducted on regular production units that allowed functions such as calibration, auto-ranging,
data logging, and reporting of data as PAH or Oil concentration.
First of all, Hach Company would like to express its gratitude to the ACT Scientists and Technicians for
conducting such a comprehensive test.
As a general observation, we would like to note that the FP360sc sensor was performing to its
specifications in each and every test. The FP360sc instrument displayed remarkable specificity to the
petroleum products and was not reacting to interfering factors such as turbidity, CDOM, chlorophyll,
etc.
A few important notes to keep in mind when reviewing results from this evaluation:
-
A good amount of research should be done when selecting a calibration standard or method to
obtain quantifiable results.
-
Scaling should be examined carefully when looking at results of the Vertical Profiling Field Test,
especially since there was a third-party data logger used for collecting data in mV format. A simple
calculation based on the minimal default incremental step change for the sensor output being 1.2
ppb of PAH (~36 ppb of Oil) can be translated into 36 mV according to the scale presented in Fig.
11-13 (p. 32-34 of the report). This shows that the spikes displayed in the figures represent just a
regular instrument noise equal to a single minimal registered step change and constituting the
specified FP360sc limit of detection (LOD).
-
Oil spill detection in the low ppm range is the most common use case for the sensor. It was
greatly simulated by the wave tank test where the probe showed excellent performance for all
types of oil used.
As it was concluded in the study, one should expect the best results when this type of sensors is used for
qualitative continuous monitoring of the water samples. The examined probe was confirmed to be an
excellent early warning device instantaneously reacting to water contamination by hydrocarbons.
Response Time and Linearity
The study confirmed the FP360sc specification on its linear response to concentrations of various types
of petrochemical products when there is no variation in the product nature. The linearity is supported
by very low sensitivity of the probe to interfering compounds found in natural or treated waters. The
probe’s response time was evaluated to be as specified by the manufacturer, however, the sensor
specifications were written in a conservative manner and real-life T
90
response time is usually within 2-3
seconds.
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