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.

Product Description

Each of our pH sensors is meticulously engineered to meet your monitoring and control needs. Low maintenance operation, rugged materials & seals, and ground loop elimination all come standard.  Just plug two wires into any pH monitoring/control system that accepts 4-20 mA inputs and enjoy years of hassle-free operation. It’s that easy.

Check out the features below to learn more about how the STs Series pH Sensor benefits your business.

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


With proper care, these sensors are designed for many years of reliable pH monitoring in harsh conditions.  The truly unique aspect of the STs Series is that every part, including the cable, is easily replaceable in the event of wear/damage.  This considerably extends their lifespan to save your company money.  It also keeps waste out of landfills to support sustainable business practices.

Ground Loop Elimination

If you ever have a pH sensor sending erratic measurements and can’t figure out why, then there may be a “ground loop”.  A ground loop occurs when the electrical circuit has multiple paths to ground that cause interference.  This issue can be very difficult to detect and fix.  The best way to avoid ground loops is with input/output electrical isolation, which is built into every pHionics sensor.

Low Maintenance

Very little is required to keep these sensors up.  Just perform periodic calibrations and replace the electrode every few years*.  Electrode replacement is a 60-second procedure that is easily performed in the field without any tools.

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  


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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