ST-765SS Series Free Chlorine or Chlorine Dioxide Sensors

Free Chlorine or ClO2 Sensor for Clean Water Applications.

Choose between the ST-765SS-FCL or the ST-765SS-CLO to measure for Free Chlorine (0-5ppm) or Chlorine Dioxide (0-5ppm) as well as pH & Temperature, with one robust smart sensor.

CE Mark  


EPA Logo    


The ST-765SS Series are stainless steel multi-parameter membrane-less sensors based on unique electrochemical principles to determine free chlorine or chlorine dioxide and pH content in water. These sensors incorporate Pyxis Lab® advanced technology in the field of bare-gold electrochemical detection. The ST-765SS-FLC sensor integrates Free Chlorine, plus pH measurement while the ST-765SS-CLO integrates Chlorine Dioxide plus pH measurement. Both can perform temperature and pH compensation for the measurement of Free Chlorine or Chlorine Dioxide based on the conditions present in the application of use. This unique internal compensation results in a highly accurate oxidizer measurement consistent with DPD wet chemistry methodology as high as a pH of 9.0 and is compliant with USEPA-334.0 & ISO-7393 guidelines.

The ST-765SS Series sensors offer a replaceable, front-loading reference electrode assembly that has been independently developed by Pyxis Lab®, eliminating the shortcomings associated with membranes and gel replacement while offering reduced polarization time on startup, offering an electrode life span potential of up to 2 years. The flat front-end design of the ST-765SSS series makes this platform less prone to contamination or fouling and is easy to clean. The ST-765SS Series sensor body is composed of 304 Stainless Steel and is well suited for aggressive environments.

The ST-765SS Series offer (2) 4-20mA and RS-485 Modbus outputs and is Bluetooth® 5.0 enabled when used with the MA-CR Bluetooth® adapter. The world’s first four-electrode composite sensor that provides three measured parameters including Free Chlorine or Chlorine Dioxide, pH and Temperature with one sensor RS-485 Modbus output. The ST-765SS is the best choice for potable water, secondary water supply, domestic water, decorative water and other clean water applications.


  • Real-Time pH + FCl (0-5ppm) or ClO2 (0-5ppm) Detection
  • Dual 4-20mA Outputs (FCl or ClO2 + pH) and RS-485
  • Bluetooth® Enabled with the MA-CR Adapter
  • Wireless uPyxis® Calibration and Cleanliness Diagnostics
  • Integrated RTD & pH Compensation to pH 9.0 of the Oxidizer Value
  • Replaceable EH-765 Reference Electrode Assembly – Simple Maintenance


Part Number ST-765SS-FCL 53607
ST-765SS-CLO 53608
Sensor Body Material 304 Stainless Steel
Oxidizer Range ST-765SS-FCL 0.00-5.00ppm FCl2 (auto-range)
ST-765SS-CLO 0.00-5.00ppm ClO2 (auto-range)
Oxidizer Precision ±0.01mg/L or 1% of the Value with pH Compensation up to 9.0
pH Range 0-14
pH Precision ±0.01
Sample Inlet Pressure 7.25-30psi (0.05-0.2MPa)
Installation FR-50 Self-Regulating Flow Reservoir with Rotameter & PRV – Included
FR-50 Min/Max Flow Rate 200-400mL/min
FR-50 Features 1/4″ OD Sample Inlet
3/8″ OD to Drain Sample Outlet
20mm to Drain Sewage Overflow Outlet
Power Supply 22-26VDC, Power Consumption – 2W
Storage Temperature -7-60 °C (20-140 °F)
Outputs Dual Isolated 4-20mA Analog
Isolated RS-485 Digital
Dimension (LxD) 8.3in (210.8mm) L x 1.4in (35.6mm) D
Weight 530g (1.16lbs)
MAX Sensor Pressure 100psi (6.9Bar)
Operating Temperature 4-40 °C (40-140 °F)
Wet Material UPVC
Regulation CE / RoHS
Compliance EPA 334.0 / ISO 7393
Cables Included MA-4.9CR Cable (8-Pin Adapters – 4.9ft)
MA-1.5CR Cable (8-Pin Adapter/Flying Leads – 1.5ft)
Typical Electrode Service Life 2 Years

Support Documents

ST-765SS Series pH + Oxidizer Sensor Data Sheet

ST-765SS Series Sensors User Manual V2.4

ST-765SS-Br Series Sensors User Manual V1.3




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