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STs Series Conductivity Sensor


The pHionics STs Series™ Conductivity is a water quality sensor (sonde) designed to pair with a datalogger or RTU for real-time data capture.  A narrow diameter allows the STs Series to go places others can’t while the chemical-resistant housing ensures the sensor can stay there for many years.  Proprietary electrode technology provides stable measurements to reduce calibration frequency.   

All parts, including the cable, are easily replaceable without tools using pHionics patented pHiConn™ System, saving frustration and money.  

In addition, isolation, differential amplification, and shielding ensure a strong signal with high signal-noise ratios, all while remaining low-power.

These features make our conductivity sensor well-suited for applications such as groundwater monitoring, wastewater treatment, aquaculture, pollution monitoring, etc.

Highlighted Features 

  • 4-cell electrode measuring conductivity (ec), total dissolved solids (TDS), or salinity depending on scaling with datalogger or remote telemetry unit (RTU) 
  • Secondary 0-50°C temperature sensor 
  • 2-wire, 4-20 mA analog outputs compatible with many dataloggers or RTUs.
  • Narrow diameter (0.75 inches or 1.9 cm) for groundwater monitoring applications 
  • Isolated to prevent ground loops
  • Holds calibration for months at a time

Conductivity Sensor Ranges Available:

  • 0-1,000 µS/cm
  • 0-5,000 µS/cm
  • 0-10,000 µS/cm
  • 0-50,000 µS/cm
  • 0-100,000 µS/cm

Quick Delivery!

Orders typically ship in 3-5 business days.

Have a question?

We have knowledgeable customer service representatives ready to help!

Business hours:

9 am to 5 pm PST – Monday through Friday

Full Features List 

  • 4-cell electrode to measure conductivity, TDS, or salinity depending on scaling 
  • Secondary 0-50°C temperature sensor 
  • Chemical-resistant Delrin®, PVDF, and 316 Stainless Steel housing (Titanium optional) 
  • Metal housing acts as the solution ground, removing background noise caused by stray electrical currents
  • Narrow diameter (0.75 inches or 1.9 cm) 
  • Electrode guard to reduce debris or algae buildup and protect from damage 
  • Fully submersible up to 70 psi 
  • Shielded, Kevlar®-reinforced, water-blocked polyurethane cable 
  • 4-20 mA signal capable of transmission up to 3 miles (with proper wire gauge)
  • Automatic Temperature Compensation (2% per degree Celsius) 
  • Reversible Input Protection and Operation 
  • Isolated to prevent ground loops 
  • Signal conditioning to remove background noise 

Low Maintenance

Reduce the number of site visits with the STs Series Conductivity sensor.  A 4-cell electrode holds calibration for long periods of time while also preventing errors due to polarization.

In addition, the guard protects the sensing elements from algae and debris build-up, further reducing the need for calibration.

Accurate Measurements

No noise. No nonsense.

Experience the difference with our proprietary noise reduction technology.

Mounting Options

Pipe mounting

Due to their small diameter and light-weight design, pHionics STs Series™ sensors may be set up in a number of ways.  They may be suspended by the Kevlar-reinforced cable down a pipe, as shown to the right, or mounted at the end of a pipe using the pHionics cmp-k compression fitting, as shown to the left and below.  

Instructions for pipe mounting are available here.



Conductivity Sensor

Output 4-20 mA
Conductivity Range 0-100,000 µS
Electrode Type 4-cell
Transmitter Type 2-wire
Automatic Temperature Compensation 2% per °C
Power Supply Voltage 8-40 VDC
Response Time 95% < 5 seconds
Pressure Range 0-70 psi
Wetted Materials 316 SS, Delrin®, Viton™, PVDF
Length 14.50 in (36.83 cm)
Width 0.75 in (1.90 cm) maximum
Weight (No cable) 0.50 lbs (0.227 kg)
Linearity ± 0.20% of full scale*
Accuracy ± 0.20% of full scale*
Sensitivity ± 0.05% of full scale

*After proper calibration

Temperature Sensor

Output 4-20 mA
Temperature Range 0-50°C
Accuracy +/- 1°C
Linearity +/- 0.5°C
Power Supply Voltage 7-40 VDC


Cable Material Polyurethane
Type 4 conductor, Kevlar® reinforced, water blocked, shielded, twisted-pair wiring
Maximum Distance 3 miles
Resistance per 1000 ft (304.8 m) 26 Ohms
Replaceable? Yes

pHionics products comply fully with all applicable EU Directives to bear the CE Mark.

Delrin® and Kevlar® are registered trademarks of DuPont™. Viton™ is a trademark of Chemours.

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