STs Series pH Sensor

Highlighted Features 

  • Combination double-junction electrode measuring 0 to 14 pH  
  • Large reference half-cell to reduce calibration frequency 
  • Secondary 0-50°C temperature sensor 
  • 2-wire, 4-20 mA analog outputs compatible with wide range of dataloggers or remote telemetry units (RTU) 
  • Narrow diameter (0.75 inches or 1.9 cm) for groundwater monitoring applications  
  • Low power usage

Ranges available:

  • 0-14 pH
  • 6-11 pH

For datalogging applications, we recommend pairing our devices with the HOBO RX3000.


The pHionics STs Series™ pH is a dual-output sensor that pairs with a datalogger or RTU for real-time water quality monitoring.  A narrow diameter allows the STs Series to go where other sensors cannot while a durable, chemical-resistant housing ensures many years in-use.  

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 pH sensor well-suited for applications such as groundwater monitoring, wastewater treatment, aquaculture, pollution monitoring, etc.

Starting at $930 USD

All STs Series base prices include a 25 ft. (7.62 m) cable.  Custom cable lengths available.


Please see our STs Series pH Sensor Price List for more information on available options and pricing. Our spare parts pricing is available here.

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Business hours:

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Full Features List

  • Combination double-junction electrode with large reference reservoir
  • Secondary 0-50°C temperature sensor 
  • Chemical-resistant Delrin®, PVDF, and 316 Stainless Steel housing (Titanium optional) 
  • Narrow diameter (0.75 inches or 1.9 cm) 
  • Removable electrode guard to protect from damage while allowing access to electrode for cleaning
  • 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  
  • 2-second warm-up time to avoid battery drain of datalogger or RTU
  • Low power usage for long-term water quality monitoring 
  • Isolated to prevent ground loops  
  • Signal conditioning to remove background noise  

Low Maintenance

The weak point of pH sensors is their reference solution, which gets diluted by the sample over time.  STs Series pH sensors mitigate this problem by incorporating a reference half cell with a large reservoir.  The high volume, combined with a low-flow reference gel and double-junction, reduces the dilution rate to provide a more stable reference. 

Accurate Measurements

No noise. No nonsense.

Experience the difference with our proprietary noise reduction technology.


pH Sensor

Output 4-20 mA
pH Range 0-14 pH
Operational Temperature Range 0-70°C
Electrode Type Silver/silver chloride, double junction, replaceable gel electrode
Transmitter Type 2-wire
Pressure Range 0-70 psi
Automatic Temperature Compensation 0-70°C
Isolation 600 VDC
Power Supply Voltage 8-40 VDC
Warm-up Time 2 seconds
Response time 95% < 5 seconds
Wetted Materials 316 Stainless Steel, Delrin®, Viton™, glass, epoxy
Length 14.25 in (36.20 cm)
Width 0.750 in (1.9 cm) maximum
Weight (No cable) 0.50 lbs (0.227 kg)
Linearity ±0.014 pH*
Accuracy ±0.014 pH*
Sensitivity ±0.01 pH
Stability ±0.03 pH per year
Repeatability ±0.01 pH

*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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