STs Series™ pH Sensor

With over 40 years in the water quality business and customers like IBM, Siemens, and Lawrence-Livermore Berkeley Labs, pHionics has the experience and pH sensors you need to succeed.

Sleek and Discrete

The STs Series goes where other pH sensors can’t.  With a 0.75” diameter, it easily fits down most wells and pipes without blocking flow.


The STs Series pH Sensor simplifies your purchasing and installation with a built-in temperature sensor.

Low Maintenance Costs

How often do you want to maintain and troubleshoot your pH sensor?  As little as possible is the consensus for most users.  Investing in the STs Series pH Sensor leads to fewer site visits and fewer problems thanks to careful engineering backed by 40 years of experience.

Keep scrolling to see the features that make this possible.

Invest in pHionics sensors for a more robust, low-maintenance water monitoring system.

Quick Delivery!

Orders typically ship in 3-5 business days.

Have a question?

We have knowledgeable engineers ready to help with your project!

Business hours:

9 am to 5 pm PST – Monday through Friday

Full Features List

  • 0-14 pH Range
  • Combination double-junction electrode with large reference reservoir
  • Built-in 0-50°C temperature sensor (2nd channel)
  • Chemical-resistant Delrin®, PVDF, and 316 Stainless Steel housing (Titanium optional) 
  • True 2-wire sensor for simple installation
  • Solution ground
  • Narrow diameter (0.75 inches or 1.9 cm) 
  • Removable electrode guard
  • 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
  • Lowest power usage compared to other 4-20 mA pH sensors
  • Isolated to prevent ground loops  
  • Signal conditioning to remove background noise  

Low Maintenance

The weak point of pH sensors is their reference electrolyte, which gets diluted by the sample over time.  STs Series pH sensors mitigate this problem by incorporating a reference half cell with a large electrolyte reservoir.  In addition, the electrolyte is solidified into a gel and two Teflon™ junctions are used to further slow dilution.


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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