ESKO12 - optical probe of dissolved oxygen in water

Tyčový snímač rozpuštěného kyslíku ESKO12


  • Luminescent optical method for measuring the concentration of dissolved oxygen
  • Accurate measurement without the need for regular calibration
  • When measuring, the sensor does not consume oxygen and therefore does not require the flow of water around the sensor
  • The ESKO12 rod probe and the suspended probe use the same S423/C/OPT sensor
  • Quick installation of the ESKO12 rod probe in the correct measuring position using the adjustable stainless steel holder DE2
  • Suspended version of the probe with S423/C/OPT sensor and 10 m long cable
  • RS485 communication interface under MODBUS RTU protocol compatible with FIEDLER units
  • Internal sensor for measuring water temperature
  • Supply voltage in a wide range from 10 to 24 VDC





Operating principle

The principle of measurement is based on the effect of dynamic luminescence quenching by molecular oxygen.

The S423/C/OPT sensor works on the principle of mea-suring the intensity of radiation on the luminescent layer of the measuring head caused by a short light pulse of high energy generated by the sensor electronics. Oxygen atoms absorb the energy of the pulse, which would otherwise be emitted in the form of photons by the luminophore atoms, and therefore the concentration of dissolved oxygen in the measured solution is inversely proportional to the measured intensity of the luminescent radiation.

The sensor also regularly measures the intensity of the low-energy reflected light luminophore (which does not cause luminescence) and uses this measured value during the sensor's own autocalibration.

Unlike Clark-type electrochemical probes, optical probes do not require regular calibrations, do not need to change electrolyte or clean the chemically worn anode.


The S423/C/OPT probe is used for the optical measure of oxygen in pure and process waters.

  • Wastewater treatment plants
  • Measure of oxygen in primary, industrial, recirculating water
  • Fishing

Features and benefits

  • The probe are placed in the measured medium at an inclination (30 to 45 degrees) to prevent the accumulation of gases on the surface of the luminophore measuring head.
  • The luminescent method of measurement does not consume oxygen during the measurement and therefore the probe does not require the flow of the measured medium around the measuring head.
  • Unlike the commonly used Clark electrochemical probes, the optical probe does not need to change the electrolyte and there is no gradual decay of the anode due to ongoing chemical reactions.
  • The probe does not require calibration by the user -automatic autocalibration takes place during each measurement.
  • After 2-3 years of operation, the luminophores in the exchangeable measuring head may be depleted. By fitting a new measuring head, the correct function of the sensor is restored. When replacing the measuring head, it is necessary to calibrate the sensor.


Rod probe ESKO12

Snímač rozpuštěného kyslíku ESKO12 s držákem DE2

The most common mechanical design of the dissolved oxygen probe for wastewater treatment plants. The rod probe can be easily installed using the DE2 holder on the railing of the activation tank or on the edge of the tank.

The ESKO12 probe includes a stainless steel tube holder and a S423 / C / OPT measuring sensor with a shortened cable so that the entire cable fits into the tube holder. The ESKO12 probe also includes an M12 / Amphenol-7 connector reducer at the upper end of the tube holder.

The ESKO12 probe is supplied with a 3 m long connecting cable, which is terminated on one side by a 7-pin Amphenol-7 connector with high IP67 protection and the other side is free. The length of the connecting cable can be extended up to 500 m.

The stainless steel tube of the ESKO12 sensor with a diameter of 40 mm can be supplied in lengths from 500 mm to 4000 mm on request.



Detail of the connector connection of the ESKO12 rod probe with the Amphenol-7 connector:

Detail konektorového připojení snímače ESKO12


Connection of pins of the ESKO12 rod probe connector:


1 +Unap (red)
2 NC
3 NC
4 NC
5 RS485-B (green)
6 RS485-A (yellow)
7 GND (black)


Holder DE2

The ESKO12 rod probe is usually attached to the measuring point using an adjustable stainless steel holder DE2.

držák DE2

The DE2 holder is two-part and, in addition to adjusting the inclination, also allows the probe in the holder to be moved, for example, according to the current water level or when cleaning the probe from coarse dirt.


Suspended probe S423/C/OPT

The suspended probe is supplied as standard with a 10 m long cable, which has a 5-pin M12 / 5F industrial connector fitted at the end.

When hanging the probe by the cable, it is also necessary to ensure the oblique position of the probe so that air bubbles do not stick to the measuring head of the S423 sensor.


Snímač rozpuštěného kyslíku ESKO12 


Connection of pins of the ESKO12 rod probe connector:


1 + Unap (red)

2 GND (black)

3 RS485-A (yellow)

4 RS485-B (green)

5 shields (black)



Dimensions of suspension probe S423/C/OPT:

Rozměry snímače ESKO12-Z

Luminophores head CAP423

The manufacturer's recommended replacement time for the probe head is 1 to 3 years, depending on the degree of depletion of the luminophores layer. It must never come into contact with organic solvents such as acetone, chloroform, benzene and toluene. Likewise, chlorine gas can irreversibly damage the head and thus affect the accuracy of the measurement.

CAP232 luminoforová hlavice

The head with the luminophor is screwed on the body by the probe and therefore the replacement of the head is relatively simple. It is recommended to calibrate the probe after each head replacement.


Basic technical parameters

Measuring methodoptical measurement of excited luminescence
Measuring range0,00 to 20,00 mg/l
Measurement accuracy+/-0,1mg/l
Response speedreaching 90% of the value in <60 sec
Measurement frequencymin 1 measurement / sec
Working temperature range-10 to +60 °C
Maximum working pressure5 bar
Dimensions ESKO12 (diameter x length)40 x 1750 mm
Sensor materialnerezová ocel, Tecaform
Diameter of the phosphor of the measuring head10 mm
Weight of rod sensor ESKO122200 g
Weight of the ESKO12-Z pendant sensor1150 g
Sensor cable length ESKO12-Z10 m, conenctor M12
Power voltage12 to 24 V DC
InterfaceRS485, protocol Modbus RTU
Temperature compensationinternal NTC
Price list