Pyxis ST-750 Inline APHA-Hazen Color Sensor

The Pyxis ST-750 is an inline sensor that measures the color of water in real time in municipal, industrial and environmental applications. The measurement is based on the APHA-Hazen platinum-cobalt (Pt-Co) method widely used in laboratories. The manufacturer describes the sensor as suited to clean or lightly polluted water with a slight to pale yellow tint, such as relatively clean surface water, groundwater, domestic and drinking water, and industrial water. In Turkey, Mikron Proses (Üsküdar, Istanbul) provides application consulting on installation and calibration planning.

Mounting point · Calibration plan → Send us your requirement

For more Pyxis inline sensors, see Online Analyzers.

Measuring principle

Besides the primary light source and detector pair that measures the color content, the sensor has a reference light source and detector pair that compensates for mild turbidity interference. The measurement is made at a wavelength of 365 nm, and the standard output range is 0.10-30.0 degrees (ppm Pt-Co); it can be extended to 500 degrees in the uPyxis app. The lower detection limit is 0.10 degrees, the resolution is 0.01 degrees, and the accuracy is stated as ±2% of reading or 0.1 degrees, whichever is greater. The manufacturer states that the method complies with ASTM D1209 and ISO 6271.

Outputs and mounting

The sensor provides an integrated isolated 4-20 mA analog output and an RS-485 Modbus digital output at the same time. The UPVC sensor comes with the standard ST-001 inline ¾ in FNPT tee fitting, a 1.5 m bulkhead cable and a 1.5 m flying-lead cable (both with IP67 quick adapters), so it can be wired quickly to any microprocessor controller, PLC or DCS. The body is 172.7 mm long, 36.6 mm in diameter and weighs 170 g; it is rated IP67 and works up to 6.9 bar (100 psi).

Maintenance and calibration

The manufacturer recommends cleaning and calibrating the sensor at least once a month (this can be reduced in clean water applications and increased in heavily fouled applications). With an MA-WB Bluetooth adapter or a PowerPACK adapter, the sensor can be accessed wirelessly from the uPyxis desktop app, which shows a live color graph and provides a calibration function. Calibration uses DI water for zero and the Pyxis COLOR-30 (30 degrees) calibration standard for slope.

Which quality parameter of your process or network water the measured color relates to, and how the mounting point (tee connection, flow rate) should be set, is reviewed together with you. Tell us your requirement and we will plan the mounting and calibration with you.