Optical dissolved oxygen sensor


  • Extremely fast and precise optical DO sensor – outstanding for field and lab applications
  • Proven green light technology for long operation life of sensor
  • Beveled membrane minimizes interference that can be caused by air bubbles
  • Universal protective armoring available
  • Low power consumption and maintenance
  • Simple to integrate and operate
  • One year sensor life

Optical Dissolved Oxygen Transmitter Product Description

The WQ-FDO Optical Dissolved Oxygen Transmitter is an instrument designed for measuring dissolved oxygen concentrations in liquids. The WQ-FDO Optical Dissolved Oxygen Transmitters were developed to meet different requirements ranging from surface water monitoring programs to harsh waste water applications. The optical dissolved oxygen transmitter has been specifically designed to meet the demanding requirements of the environmental monitoring and scientific research sectors, providing long term, accurate and reliable dissolved oxygen measurement. The WQ-FDO Optical Dissolved Oxygen Transmitter has extremely low power requirements and a 4-20 mA output making it ideal for incorporation into remote environmental monitoring installations.

Methodology – Optical Dissolved Oxygen Transmitter
The WQ-FDO Optical Dissolved Oxygen Transmitter’s optical measuring technology is based on an attenuated fluorescent signal measured in a defined time frame.  A fluorescent dye is stimulated in the optical dissolved oxygen sensor’s membrane by a short wave length light source.  By falling back into the passive state, long wave light is emitted, which is recorded as a measurement signal.  If oxygen contacts the dye by diffusing through the membrane the period of back scattering light is shortened according to the oxygen concentration of the sample.  The optical dissolved oxygen measurement is more or less a highly precision time measurement.  In order to process this time measurement as precisely as possible, the optical dissolved oxygen sensor optics are calibrated to the speed of light.

Optical Dissolved Oxygen Transmitter Advantages
The WQ-FDO Optical Dissolved Oxygen Transmitter has many advantages over traditional DO sensors.  Unlike conventional galvanic and polargraphic dissolved oxygen sensors, WQ-FDO optical dissolved oxygen transmitters have no consumable cathodes or anodes that require replacement, minimizing servicing requirements.  Neither do the optical dissolved oxygen transmitters consume oxygen.  Consequently the measurement of dissolved oxygen by the optical dissolved oxygen sensor is unaffected by water flow.  The WQ-FDO optical dissolved oxygen transmitters can even be deployed in stagnate groundwater bores.  The WQ-FDO optical dissolved oxygen transmitters have extremely stable electronics – a calibration interval of 1 year is typical.

The measuring and reference path optical components are identically designed inside this optical dissolved oxygen sensor. Natural aging processes of the optical dissolved oxygen sensor’s optical components can therefore be compensated by the reference path and accordingly compensated in the measuring path. As a result, the optical dissolved oxygen transmitter provides accurate dissolved oxygen measurements over long periods of time without the need for re-calibration. Additionally by stimulating the fluorescent reaction in the membrane with low energetic green-light, the fluorescent dye in the sensor membrane won’t be bleached out.

The WQ-FDO optical dissolved oxygen transmitters can be used to monitor dissolved oxygen in almost any liquid, including wines, beer, and milk. The optical dissolved oxygen sensors are not affected by color of the liquid. With the beveled membrane design bubbles or aeration do not affect the optical dissolved oxygen transmitter’s measurements. There is no chemical interference from typical wastewater chemicals and the optical dissolved oxygen transmitters can withstand harsh wastewater applications.

Global Water’s PC320 Optical Dissolved Oxygen Controller can use the optical dissolved oxygen transmitter’s 4-20mA output to control pumps or alarms.  In addition Global Water offers the GL500 optical dissolved oxygen recorder which adds recording capabilities and the ability to report DO concentration and saturation measurements from the 4-20mA optical dissolved oxygen transmitter.  The GL500 optical dissolved oxygen recorder connects to the optical dissolved oxygen sensor’s 4-20mA output, along with optional conductivity and barometric pressure sensors, to record highly accurate dissolved oxygen data.

Optical Dissolved Oxygen Sensor Product Applications

  • Long term monitoring of dissolved oxygen in streams, rivers and lakes
  • Scientific research projects, both long and short term projects
  • Water quality monitoring around industrial outfall
  • Homeland security
  • Thermocline profiling
  • Fish farm and aquaculture water quality monitoring
  • Wastewater industry
  • Food and wine industry

Optical Dissolved Oxygen Transmitter Specifications

Dissolved Oxygen
Partial pressure: 0-400 mbar
Accuracy: ± 0.5 % of value
Repeatability: 0.01 ppm
Response time: 90% in less than 60 seconds
Sensor Drift: Less than 1% per year
Temperature: Compensated 32 to 122°F (0 to 50°C)

Accuracy: ±0.2°F (±0.1°C)
Resolution: 0.02°F (0.01°C)
Range: 32 to 122°F (0 to 50°C)

Maximum Pressure: 35 PSI (25 m/82 ft water depth)
Output: Dual 4-20 mA (Partial Pressure and Temperature)
Operating Voltage: 10-30 VDC
Current Draw: 24 mA plus both sensor outputs
Warm Up Time: 6 seconds minimum, 8 recommended
Operating Temperature: 32 to +122°F (0 to +50°C)
Size of sensor: 8 inch L x 0.86 inch Diameter (202 mm L x 22 cm Dia.)
Sensor Construction: Acetyl, stainless steel, cast epoxy
Weight: 8 oz (227 g) plus cable

Optical Dissolved Oxygen Transmitter Options

WQ-FDO Optical Dissolved Oxygen Transmitter (PN# DD0500)
Includes 25 ft of cable.  Does not include armoring.

WQ SC-FDO Optical Dissolved Oxygen Transmitter Replaceable Membrane (PN# 201330)

WQEXC Extra Cable (PN# DH0000)
Standard Optical Dissolved Oxygen Sensors include 25 ft of cable, but can be purchased with up to 500 ft of cable.


Optical Dissolved Oxygen Transmitter Plastic Armor (PN# DD0505)

Optical Dissolved Oxygen Transmitter Stainless Steel Armor (PN# DD0510)


Multi 3410 Digital Multiparameter Meters
Includes Digital Multiparameter Meter and choice of electrodes.

DO600 Dissolved Oxygen Meter
Includes DO electrode, protective sensor cap, spare membrane cap, electrolyte, four 1.5V SR44W batteries, and a 48 inch (1.2m) neckstrap.

DO610 Dissolved Oxygen Probe Kit
Includes EC500 Conductivity/TDS/Salinity/pH/Temperature meter, DO600 Dissolved Oxygen probe, and accessories.

DO200ACC Field Dissolved Oxygen Meter Kit
Includes field DO meter, cable with attached DO/temperature probe, and hard sided case.

2BA103 Oxi 3205 Set Handheld Dissolved Oxygen Meter Set
Includes dissolved oxygen meter, DurOx® 325-3 dissolved oxygen probe (9.8ft cable), case & accessories.

3B30-010 Oxi 1970i Portable Dissolved Oxygen Meter w/universal power supply

WQ401 Dissolved Oxygen Sensor

GL500-7-2 Optical Dissolved Oxygen Recorder
Optical dissolved oxygen recorder for sensor datalogging.  Includes Global Logger Software.  With weather proof enclosure and 12V battery.

PC320 Optical Dissolved Oxygen Controller

EZ100 pH Sensor Display
LCD readout display for both portable use and permanent installations.