The pHionics STs Series™ ORP sensor provides reliable ORP (redox) and temperature measurements to a datalogger, RTU, PLC, or SCADA system for continuous water quality monitoring.

Accurate and low-maintenance operation is ensured with noise-resistant 4-20 mA analog signals and a large-volume, double-junction electrode. Typical electrode life is 2-4 years and, when needed, a replacement is easily installed thanks to pHionics’ patented pHiConn™ Connector System. In addition, the electronics are isolated to prevent ground loops and proprietary signal conditioning virtually eliminates background noise.

Durability is guaranteed with chemical-resistant 316 Stainless Steel (titanium optional) and high-quality double O-ring seals that last many years, even in harsh conditions. When combined with the compact design (0.75 in. or 19 mm diameter), this ORP sensor proves to be compatible with a wide range of applications.

If you need a sensor that works anytime, anywhere, for many years, then the pHionics STs Series ORP sensor is here for you.

Highlighted Features

• Replaceable electrode with platinum sensing element measuring -1000 to +1000 mV oxidation-reduction potential (ORP)
• 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

Low Maintenance

The weak point of ORP sensors is their reference solution, which gets diluted by the sample over time.  STs Series ORP 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 junction, reduces the dilution rate to provide stable measurements with less calibration.

Accurate Measurements

Applications

• Groundwater Monitoring
• Agricultural Runoff
• Mining Pollution
• Industrial Effluent Monitoring
• Wastewater Treatment
• Environmental Remediation
• Aquaculture
• Chlorine Level Monitoring

*After proper calibration

What is the proper way to store an ORP electrode?

Please see our STs Series Storage guide >>

How often should the STs Series pH be calibrated and/or cleaned?

The frequency of calibration must be determined empirically as rate of drift and debris accumulation differs for each application. Calculating the offset during calibration provides information on whether the electrode is still viable.  See our article on Proper Sensor Calibration for assistance in the process.  Check out our pH Electrode Care Guide for cleaning and troubleshooting procedures.

How long does the electrode last?

ORP (redox) electrodes last an average of three years.  Electrode life varies significantly based on the qualities of the solution being measured (pH, flow rate, ion concentration etc.) and can range from 6 months to 5 years.

Do you provide a warranty?

Yes, our products come with a 2-year warranty, excluding the electrode. These products are designed to last far longer if properly cared for and we will do what we can to help if any problems occur in or out of warranty.  Please don’t hesitate to reach out!

Read our full warranty here >>

What voltage is required for the STs Series ORP?

An 8VDC power supply is sufficient with standard lengths of cable.  Voltage drop must be accounted for over long lengths of cable (50+ ft.) to ensure enough power is supplied to any water quality sensor.  To calculate it, first double the length of cable to get the account for the full length of the circuit, then multiply that by resistance per foot/meter to get total resistance.  pHionics uses 24 AWG tinned-copper wire which has a resistance of 0.026 ohms per foot (0.084 ohms per meter).  Multiply total resistance by the maximum expected current (20 mA, or 0.02 A, is safest) to obtain expected voltage drop.  Verify that the voltage drop plus required voltage for pHionics sensors (8 VDC) is less than the power supply voltage.

How long are STs Series devices expected to last?

While the electrode will require replacement every three years on average, the housing, seals, and cables are intended to last 10-20 years with proper care. To increase longevity of the seals, the Viton O-rings should be relubricated with a silicon grease during each disassembly, or at least inspected for any debris or damage.  The harshness of the solution (high/low pH, extreme salinity, high pressure, etc.) also affects longevity.  All parts are replaceable to save money and limit waste in the event that any piece gets damaged.

What type of electrode is provided?

We provide a combination electrode with silver/silver chloride reference wire that has Teflon double junctions and a platinum band.  It is replaceable instead of refillable to reduce maintenance time.

What spare parts are recommended?

For critical measurements, a duplicate STs Series sensor is always recommended so a replacement for every part is always available.  A duplicate simplifies troubleshooting by having a functional STs Series on-hand to compare results.  It also allows for swapping of devices during calibration and cleaning so the measurement or process is not significantly disrupted.  At a minimum, a spare electrode is recommended in the event of damage–or the need for eventual replacement.  This is especially important when waiting for a replacement to be shipped could be detrimental to your application.

Is the output automatically temperature-compensated (ATC)?

No, ORP (redox) is a general reading that varies with temperature drastically depending on the chemical properties of the solution being measured.  Standardization to a given temperature is not useful for a majority of applications.

How can the STs Series be installed/mounted?

The STs Series can be mounted in-line or immersed with the cmp-k compression fitting in a 3/4″ pipe, or freely suspended by the Kevlar™ cable.  Please see the pHionics STs Series Device Manual or contact us for more information.