Pyxis ST-600 Series Inline Disinfectant Concentration Sensors

The Pyxis ST-600 series are inline sensors that measure the concentration of the raw or concentrated disinfectant solution itself, in percent by mass and without dilution, using UV absorbance. This is a different job from the ppm-level residual measurement of the Pyxis ST-765SS-FCL free chlorine and pH sensor. Three models apply the same principle to three concentration ranges and applications. In Turkey, Mikron Proses (Üsküdar, Istanbul) provides application consulting on model and mounting selection.

Model selection · Mounting method · Calibration → Send us your requirement

For more Pyxis inline sensors, see Online Analyzers.

Measuring principle: UV absorbance without dilution

Besides the UV light source and the main detector, the sensor contains a reference light source and detector. This second channel gives long-term measurement stability. The sensors are factory calibrated with ultra-pure sodium hypochlorite and chlorine dioxide solutions; the manufacturer notes that raw material quality varies worldwide and that field calibration may be required when lower-quality raw material is used. RTD temperature compensation corrects the effect of temperature on the measured concentration and provides a temperature output signal.

Three models, three ranges

ST-600 measures manufactured liquid bleach (NaOCl) concentrate, or the precursor for monochloramine generation, in the range 0.01-16.0% mass/mass. ST-601 is designed for chlorine dioxide solution generated on site, in the range 0.01-0.35%. ST-604 covers hypochlorite generated by electrolysis, in the range 0.01-2.00%. All three have the same accuracy (±2% of reading or 0.1 percentage points, whichever is greater) and the same UPVC body.

Installation: tee for high flow or Teflon tubing for low flow

On high-volume chemical lines, the ST-001 inline tee (¾ in NPT) is used. In low-flow applications, ¼ in OD clear Teflon tubing is passed through the optical channel of the sensor. The optical channel is a compression-fitted quartz tube; for applications with extreme caustic content outside global industrial bleach quality specifications, the manufacturer recommends the Teflon tubing installation so that the chemical does not touch the optical channel.

Wireless diagnostics and calibration

With the MA-WB Bluetooth adapter or a PowerPACK auxiliary box, the uPyxis app runs a sensor cleanliness diagnostic in 5 seconds. If fouling is found, a two-point calibration can be done wirelessly after cleaning. When the sensor is connected over RS-485 Modbus, the cleanliness diagnostic data can also be passed to your own controller as a register. The manufacturer states a typical maintenance and calibration interval of 6 months.

Which model (ST-600, ST-601 or ST-604) and which mounting method (tee or Teflon tubing) suits your process line depends on the type of disinfectant, the expected concentration range and the line flow. Tell us your requirement and we will select the right model and mounting combination together with you.