Instruction manual

3
1. Introduction
The Pyxis ST-500 inline fluorometer probe measures the concentration of fluorescence tracer PTSA
(pyrenetetrasulfonic acid) in water. It can be simply inserted to the compression fitting port of a
custom made tee. The companion tee has two ¾ inch female NPT ports and can be placed to an
existing ¾ inch sample water line. The 4-20mA current output of the ST-500 probe can be connected
to any controller that accepts an isolated or non-isolated 4-20mA input. The ST-500 probe is a smart
device. In addition to measuring fluorescence, the ST-500 probe has extra photo-electric
components that monitor the color and turbidity of the sample water. This extra feature allows
automatic color and turbidity compensation to eliminate interferences common in real-world
samples.
The Pyxis ST-500 probe has a short fluidic channel. It can be easily cleaned. The fluidic and optical
arrangement of the ST-500 probe is designed to overcome shortcomings associated with other
fluorometers that have a distal sensor surface or a long, narrow fluidic cell. These fluorometers are
susceptible to color and turbidity interference and fouling, and difficult to be cleaned.
The Pyxis ST-500 probe uses a narrow wavelength band gallium phosphide photodiode and high
temperature-tolerant and humidity-resistant optical filters. This combination greatly enhances the
robustness of the probe. It can be operated under a wide range of ambient conditions without the
need of humidity and temperature regulation. The performance of the ST-500 probe can be stable
and consistent for a long period time.
Other features of the ST-500 probe include:
 Menu-driven calibration procedure via a computer USB port. Any standard containing PTSA in
the range of 40 to 200 ppb can be used for the calibration. The standard could be the water
sample itself if the PTSA concentration of the sample is measured by an offline fluorometer. This
allows the ST-500 probe to be calibrated online without being removed from the system.
 Automatic compensation for turbidity up to 150 NTU and color created by up to 10 ppm iron or
equivalent to 10 ppm humic acid.
 The probe can be configured to an ultra sensitive mode, allowing PTSA monitoring at the 0 to 10
ppb range.
 Diagnostic information (probe fouling, color or turbidity over range, failure modes) are available
via Modbus RTU (ST-500B).
 30 day history data are stored in the probe and can be downloaded as a csv file to a PC via a UBS
connection (ST-500B).
 The ST-500 probe can be easily removed from the system without the need of any tools for
being cleaned.
1.1. ST-500 Series