Pyxis ST-765P and ST-766SS Series Oxidizer Sensors

The Pyxis ST-765P and ST-766SS are two more members of the Pyxis oxidizer sensor family, next to the 304 stainless steel ST-765SS platform. The ST-765P carries the same measuring principle in a plastic body for clean water. The ST-766SS is a 316L stainless steel platform that adds ORP and conductivity to pH and is offered in many oxidizer versions. In Turkey, Mikron Proses (Üsküdar, Istanbul) provides application consulting on selecting the oxidizer parameter, body material and mounting.

Oxidizer selection · Body material · Flow assembly → Send us your requirement

For the stainless steel ST-765SS platform, see the ST-765SS-FCL free chlorine and pH sensor and the other ST-765SS oxidizer and pH sensors. For more Pyxis inline sensors, see Online Analyzers.

ST-765P series: plastic-bodied sensor for clean water

The ST-765P uses the same membrane-less, bare-gold electrode principle as the ST-765SS; the difference is the plastic body in place of 304 stainless steel. The free chlorine (ST-765P-FCL) and chlorine dioxide (ST-765P-CLO) models measure 0.00-5.00 ppm with an accuracy of ±0.01 mg/L or 1% of the value, pH-compensated up to pH 9.0. All models share the same body size (210.8 mm × 35.6 mm, 530 g) and the replaceable reference electrode head.

The ST-765P-DCL is a four-electrode sensor that measures free chlorine (0.00-5.00 ppm) and sulfite (0.00-100.00 ppm, auto-range) at the same time. It is documented in the same datasheet (P/N 59907) as its 304 stainless steel counterpart, the ST-765SS-DCL, and is intended for dechlorination (chlorine scavenger) processes. On the FCL and CLO models, the FR-50 flow reservoir is sold separately. On the DCL model, the ST-007 tee is used for clean water and the FR-300-PLUS auto-brushing reservoir for dirty water; the FR-300-PLUS is required in dirty water applications.

ST-766SS series: pH, ORP and conductivity added

The ST-766SS keeps the same bare-gold electrochemical sensing in a 316L stainless steel body and widens the measuring set: every model gives pH, ORP (redox potential) and conductivity at the same time as the oxidizer. pH and temperature are used for compensation of the oxidizer reading, ORP directly indicates whether the water is in an oxidizing or a reducing state, and conductivity is included as an auxiliary parameter so that no separate conductivity sensor is needed. The newly enhanced Oxi-Logic replaceable dual-gold electrode head (EH-766 family) gives a typical service life of 2 years without membrane or gel replacement.

The model suffixes cover the following oxidizers and parameters:

• FCL / CLO / TCL / NCL / TFCL: free chlorine, chlorine dioxide, total chlorine, monochloramine, or free plus total chlorine; all 0.00-5.00 ppm, ±0.01 mg/L or 1%.
• O3 / Br: ozone (0.00-2.00 ppm) and bromine (0.00-5.00 ppm), ±0.01 mg/L or 1%.
• H2O2 / PAA: hydrogen peroxide (0.00-200.00 ppm) and peracetic acid (0.00-100.00 ppm), ±0.5 mg/L or 1%.
• SO3 / DCL: sulfite (0-100 ppm, ±0.5 mg/L or 1%) or free chlorine plus sulfite dual measurement (DCL).
• DBNPA: 0-20 ppm, ±0.05 mg/L or 1%.

On all models, the pH range is 0.00-14.00 (±0.01), ORP is ±1,500 mV (±1.0 mV) and conductivity is 0-10,000 µS/cm (±5%). The response time is T95 ≤ 240 seconds for the oxidizer and T95 ≤ 5 seconds for pH, ORP and conductivity, taken from the ST-766SS datasheet itself. The operating temperature is 4-49 °C and the inlet pressure is 0.05-0.6 MPa (7.25-87 psi).

Mounting options

For clean water applications, ST-007 or ST-009 stainless steel tee connections (200-400 mL/min, rotameter not included) or the FR-50 self-regulating reservoir with rotameter and PRV included (600-1,800 mL/min) can be used. For harsh or dirty water, the FR-306-PLUS auto-brushing flow reservoir (200-800 mL/min, 200 RPM motorized brush, detergent injection port, controlled by RS-485 or a 24 VDC relay) is used.

Which oxidizer parameter and which body material (plastic ST-765P or 316L ST-766SS) suits your process depends on water quality, pressure range and the existing automation infrastructure. Tell us your requirement and we will select the right model and mounting combination together with you.