
1 Introducon
The Pyxis ST-500 series inline uorometer probes measure the concentraon of uorescence tracer PTSA
(pyrenetetrasulfonic acid) in water. The standard ST-001 Tee Assembly provided with each ST-500/ST-500RO
sensor, has two 3/4” female NPT ports and can be placed to an exisng 3/4” sample water line. Pyxis Lab
also oers 2” and 3” Tee formats for larger ow installaons. 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 series probes are smart devices. In addion to measuring uorescence, the ST-500 series probes have
extra photo-electric components that monitor the color and turbidity of the sample water. This extra fea-
ture allows automac color and turbidity compensaon to eliminate interference commonly associated
with real-world waters.
The Pyxis ST-500 series probes have a short uidic channel and can be easily cleaned. The uidic and op-
cal arrangement of the ST-500 series probes are designed to overcome shortcomings associated with other
uorometers that have a distal sensor surface or a long, narrow uidic cell. Tradional inline uorometers
are suscepble to color, turbidity interference, and fouling, making them very dicult to properly clean.
The Pyxis ST-500 series probes use a narrow wavelength band gallium phosphide photodiode and high
temperature-tolerant and humidity-resistant opcal lters. This combinaon greatly enhances the robust-
ness of the probes. It can be operated under a wide range of ambient condions without the need of
humidity and temperature regulaon. The performance of the ST-500 series probes can be stable and con-
sistent for a long period of me.
2 Specicaons
Specicaon*ST-500 ST-500RO ST-500SS
P/N 50661 50669 50700
Range (ppb) 0-300 0-40 0-300
Resoluon (ppb) 0.01
Accuracy ±1% of reading
Calibraon Two-point calibraon against standard soluon
Outputs 4-20mA Analog Output, RS-485 Digital Output with Modbus protocol
Installaon†Custom tee assembly (P/N: ST-001) with 3/4” female socket & NPT threaded ports
Cable Length 5 with IP67 connectors
Power Supply 22-26 VDC, 1 W
Dimension inch (mm)‡Length: 6.8 (172.7), Body Diameter: 1.44 (36.6)
Weight lbs (g) 0.37 (170) 0.37 (170) 2.5 (1130)
Material CPVC CPVC 304 Stainless Steel
Operaonal Tempera-
ture °F (°C) 40-104 (4-40) 40-104 (4-40) 32-104 (0-40)
Storage Temperature °F
(°C) 20-140 (-7-60)
Pressure psi (MPa) Up to 100 (0.7) Up to 100 (0.7) Up to 290 (2.0) at 149 °F (65 °C)
Enclosure Rang IP67
Regulaon CE
*With Pyxis’s connuous improvement policy, these specicaons are subject to change without noce.
†The ST-500SS probe does not come with the custom tee assembly (P/N: ST-001). It has 3/4” female NPT threaded ports on the probe
itself.
‡See Figure 4 for ST-500SS dimensions.