Pyxis ST-772 Dissolved Oxygen Sensor and LT-73X Ultra-Low Turbidity Sensors

The Pyxis ST-772 is an optical luminescent dissolved oxygen (DO) sensor and the LT-73X is a family of ultra-low turbidity sensors. This page gives the model-level specifications, mounting options and application areas of both product families. In Turkey, Mikron Proses (Üsküdar, Istanbul) provides application consulting on model and mounting accessory selection.

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

For background, see the guides on optical dissolved oxygen sensors and drinking water turbidity. For higher turbidity ranges, see the Pyxis ST-730 series.

ST-772 series: optical luminescent DO measurement

The ST-772 measures dissolved oxygen by the principle of fluorescence quenching; unlike classic membrane-based electrochemical probes, it does not consume electrolyte or membrane. With dual blue and red light detection it offers a wide measuring range (0.004-20 mg/L, or 0-200% saturation / 0-500 mbar pO₂) and a very low detection limit; built-in temperature and pressure sensors compensate automatically for ambient conditions. The front-loading DCC-1 membrane cap uses a black microporous PTFE membrane material that is scratch resistant, and has a flat front end that is less prone to fouling; its typical service life is 2 years, and the sensor needs no recalibration during this time.

Four model variants are offered: ST-772 (304 stainless steel) and ST-772-P (CPVC) for submersed and floating applications; ST-772T (304 stainless steel) and ST-772T-P (CPVC) for inline and by-pass flow installations, supplied with the ST-001 tee. All models provide an isolated 4-20 mA analog output and an RS-485 Modbus digital output at the same time. With the MA-CR Bluetooth adapter and the uPyxis app, wireless diagnostics and calibration are possible (slope with air or air-saturated water; zero with a 5% sulfite solution or nitrogen gas). The ST-772 series complies with USEPA 40CFR Part 136.3 as an approved method for measuring dissolved oxygen in wastewater, drinking water and direct discharge.

LT-73X series: ultra-low turbidity measurement

The LT-73X is an inline turbidity sensor with a quartz glass flat end, working in a 90° surface scatter configuration; the flat design reduces air bubble interference and makes cleaning easier. The family offers six models in the same body: LT-736 / LT-736B (0.002-1,000 NTU), LT-739 / LT-739B (0.001-40 NTU) and LT-737 / LT-737B (0.001-5 NTU). The “B” suffix denotes the 860 nm infrared (IR) LED, and the standard models use a warm white LED. White light models are for applications that require EPA-180.1 compliance and IR models for ISO-7027. When kept clean, the sensors can run for up to 1 year without recalibration with a drift below 0.02 NTU per year (LT-736 / LT-739) or below 0.01 NTU per year (LT-737); they draw 1.5 W from a 22-26 VDC supply and provide 4-20 mA and RS-485 Modbus outputs.

Mounting uses one of two flow accessories. The FR-100 flow reservoir, designed for drinking water applications, works in by-pass at 200-400 mL/min and separates air bubbles and coarse particles (including iron and manganese precipitate) before the measurement. For industrial and pressurized lines, the FT-100 inline tee works at up to 40 L/min and up to 6.9 bar. When emptied and cleaned, both accessories can also be used for the zero-point calibration of the sensor. With the MA-CR Bluetooth adapter and the uPyxis app, liquid-less calibration with the solid-state calibration kit is also possible. The LT-73X can additionally be calibrated with the L-CAL portable liquid formazin calibration kit: the sensor is placed in the kit in a horizontal position, an integrated air vent line removes bubbles, and 500 mL of formazin standard solution is used per calibration.

Mounting accessories and calibration

For the ST-772, the MA-150-1 (floating submersion) or MA-120-B (fixed submersion) adapter kits are available; for the LT-73X, the FR-100 and FT-100 flow accessories. Both product families share the same wireless diagnostics and calibration infrastructure with the MA-CR Bluetooth adapter and the uPyxis app. Which model and mounting accessory suits your process depends on the type of measuring point (submersed or inline), the flow rate and the compliance requirement (ISO-7027, EPA-180.1, USEPA 40CFR 136.3). Tell us your requirement and we will select the right model combination together with you.