ST-500 Inline PTSA Sensor

The Industry’s Most Reliable PTSA Sensor

Measures for PTSA at an expanded range (0–300ppb), while simultaneously compensating for Color & Turbidity Interference, to provide a more accurate dosage reading. Use the MA-WB Bluetooth® Adapter to enable wireless monitoring, calibration & cleanliness diagnostics via the uPyxis® app!

CE Mark 


(2 customer reviews)


The ST-500 inline fluorometer is a very popular model for real-time monitoring of inhibitor dose. With its extreme accuracy and proven robustness in the application of fluorescence traced cooling programs. It is mostly used for feedback control to maintain the dosed concentration within a narrow band around the set point. Regardless of changes in cycle or heat load dynamics.

Now the ST-500 series expands the target of measurement to a broad range of analytes. Including fluorescein and naphthenic disulfonic acid (NDSA) to bring your success of traced cooling programs to boiler and other applications.

State-of-the-art fluorescence technology adopted in our design makes the ST-500 series well suited for real world sample water conditions. With its flow-through optical design and multiple wavelength color/turbidity compensation algorithm, the ST-500 probe keeps high performance for water samples with up to 100 NTU turbidity and/or 5ppm iron. The comparison in the experiment shown below clearly demonstrates the superior performance of the Pyxis Lab® ST-500 probe in the presence of iron color.


Item ST-500 Inline PTSA Sensor
Part Number 50661
PTSA Output Scale 0-200ppb
PTSA Max Range via uPyxis® 0-300ppb
PTSA Precision/Accuracy ±1ppb
Excitation/Emission LED 365/410nm
Power Supply 22-26VDC, Power Consumption – 1W
Outputs Isolated 4-20mA Analog & Isolated RS-485 Digital – 7-Pin
Installation ST-001 Inline Tee (PROVIDED), 3/4inch FNPT
Weight 170g (0.37lbs)
Operation Pressure 100psi (6.9Bar)
Operation Temperature 4-49 °C (40-120 °F)
Storage Temperature -20-60 °C (40-120 °F)
Material CPVC
Rating IP67, Dustproof & Waterproof
Regulation CE + RoHS
Dimensions 6.8in (172.7mm) L x 1.44in (36.6mm) D
Cable Length 5ft, Terminated with IP67 Adapter + 1.5ft Flying Lead

Support Documents

ST-500 Series User Manual V3.08

ST-500 Series Data Sheet

2 reviews for ST-500 Inline PTSA Sensor

  1. Rayford

    May I simply just say what a comfort to find somebody that actually knows what they’re discussing online. You definitely realize how to utilize fluorescent technology. A lot more people have to check this out! It’s surprising you’re not more popular given that you surely possess the gift.

  2. Dmitri

    Perfect, reliable and precise. Excellent technical support. I prefer to use Modbus and it is magnifique. Turbidity sensor inside (enough for my purposes) and it can be also calibrated (not directly but with modbus commands).
    Good luck!

    • Jake

      Thank you so much for the supportive comment! We are so excited that someone with such a great reputation in the industry has approved of our product!

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