Wednesday, 08 04th

Last updateMon, 15 Sep 2014 5am

ST 6115
Optical dissolved oxygen
2-wire 4/20 mA transmitter


This unique submersible probe has been designed to measure dissolved oxygen based on fluorescent technology. 

The measuring system consists of: 

optical device complete with a layer of fluorescent material, electronic circuit with an exciting beam for the fluorescence detection,
built-in 2-wire 4/20 mA transmitter;
digital input for calibration and configuration
nozzle for the autoclean by external pressure air 

The automatic temperature compensation is done internally by means of a built-in sensor. 

Thanks to its 4/20 mA isolated output, the probe can be directly connected to a PLC or data logger, without using amplifiers or other devices. 

The probe can be connected to B&C Electronics controller BC7635 and BC7335, which provides the power to the probe, the measuring readout, 2 set-points and an alarm, the hold during the cleaning cycle. 

The most common applications of this probe include: water quality monitoring, municipal and industrial water treatment and aquaculture. 

Principle of operation 

A light beam of a specific wavelength is sent to a special fluorescent layer in contact with the sample. 

The absorbed light energy is partially released as a light pulse with an higher wavelength

This phenomena is called fluorescence. 

If oxygen molecules are in contact with the sensing layer, the fluorescing is reduced (quenching). 

By measuring the amount of quenching it is possible to determine the oxygen concentration. 

The advantages of this measuring method are the absence of electrolyte and membrane, the possibility to measure the oxygen concentration in water or in air, and a good sensitivity in a low oxygen concentration. 


Measuring method                          : optical
Scale                                                  : 0-20 ppm
Sensitivity                                          : +/- 0,5 % of the scale
Response time                                 : 95% in < 60 seconds
Power supply                                    : 9/36 Vdc
Isolated output                                  : 4/20 mA current Loop
Load                                                   : 600 Ω max. at 24 Vdc
Temperature compensation           : automatic
Room temperature                           : -5/50 °C
Max. Pressure                                  : 10 Bar at 25 °C
Length                                               : 165 mm total
Diameter                                            : 60 mm
Body                                                   : PVC
Cable                                                 : 10 m (100 m max.)
Installation                                        : submersible
Autoclean                                          : by pressure air 3 bar max
Protection                                          : IP 68
Sensing element life                       : > 1 year, protected from light replaceable by 

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