ST-730 Series are designed for monitoring the middle range turbidity in various applications. It is more robust and tolerant to fouling, particular matters, and air bubbles comparing to other online turbidity meters designed for relatively clean water applications.

It also offers desired resolution and accuracy comparing to high turbidity or commonly referred to as suspended solid meters (4000 to 9999 NTU).

ST-730 series turbidity probe measures two optical densities and two scattering intensities at two wavelengths. This helps measure a large turbidity range and yet maintain a fine resolution. This design also helps the probe run self-diagnoses.

Typical Applications

  • Industrial water treatment process control, including raw water, cooling water, and wastewater.
  • Surface water monitoring.
  • Other chemical processes with middle range of turbidity.


  • Dual-wavelength: white LED and IR LED 90° scattering to achieve more reliable and accurate reading in a complex flow system.
  • A small footprint compact design, similar to an industrial pH probe.
  • Isolated 4-20mA output. No need for additional transmitter for easy connection to PLC and DCS.
  • Isolated RS-485 output embedded for easy trouble shooting and calibration.


ST-730 ST-731 ST-730B ST-735
Range 0~100 NTU 0-10 NTU 0~500 NTU 0~4,000 NTU
Resolution 0.1 NTU 0.05 NTU 1 NTU 10 NTU
Accuracy ±2% of reading or 1 NTU whichever is greater
Method Nephelometric, with light sources of White LED and IR LED (860nm)
Power Supply 22-26V DC, Power Consumption ~1W
Outputs Isolated 4-20mA Analog Output
Isolated RS-485 Digital Output, Supporting MODBUS protocol
Dimension Length 6.8 inch, body diameter 1.44 inch
Weight 0.37 pounds
Installation Custom tee with 3/4” NPT ports
Material CPVC
Pressure Up to 100 psi
Temperature Operation 40-120 °F, Storage 20~140 °F
Cable Length 5 feet, terminated with IP67 connectors.
30 feet, 60 feet extension cables available
Calibration Two point calibration against standard solutions
Rating IP66
Regulation CE marked