The measuring principle:

The   inner   sensor   volume   is   separated   from   the   sample   by   means   of   a   gaspermeable   silicone   membrane.   Liquids   and   solids   are   not   able   to   pass   themembrane. If the sensor is dived into a sample, the CO2  partial pressure equali-sation  is achieved between the inner sensor volume  and the sample.  Inside thesensor there is an optical sensor mounted. It's working principle is based on theSingle-Beam   Dual   Wavelength   NDIR.   This   measurement   of   the   CO2   partialpressure  has  to   be  accompanied   by the   measurement  of  the  temperature  in   thewater and by the air pressure for calculating the carbon dioxide concentration.

Main features of the Carbon Dioxide Sensor:

- submersible direct reading sensor for natural and industrial waters and sea water
- detects CO2 and total inorganic carbon when measuring additionally pH
- no signal interferences to silicate, phosphate, HCO3- and CO32-
- built-in reference measurement for superior stability
- calibration coefficients stored internally
- for depths of up to 1,000 m
- less than 0.5 W power consumption
- with analogue or digital output
- with internal temperature compensation
- compensation of humidity and other influences
- heated sensor head to avoid condensation

The optical carbon dioxide sensor has some advantages compared with the so called m-method, becausethere are no signal interferences to silicate, phosphate, HCO3- and CO32- as found in a comparison.

Technical data of the membrane covered optical carbon dioxide sensor:

Carbon Dioxide:  
 -Measuring ranges: 15 mg/l, 50 mg/l, 340 mg/l and others on request (please select one)  
 -Accuracy:    0...5 mg/l CO2: ± 0.06 mg/l  
5...15 mg/l CO2: ± 2 % of the measuring value
15...50 mg/l CO2: ± 3.5 % of the measuring value
50...80 mg/l CO2:± 1.5 mg/l CO2
80...340 mg/l CO2: ± 6 mg/l CO2

General:
- Dimensions: 225 mm length, 33 mm diameter
- Housing material: Titanium
- Connector: Subconn MCBH4M
- Power supply: 12-30 V DC when using the digital or voltage output or       20-30 V DC when using the current output
- Power consumption:< 0.5 W
- Warm up time: < 12 seconds, < 2 minutes for full accuracy
- Maximum deployment depth: 1,000 m/1,000 dbar
- Available outputs: 4...20 mA, 0...5 V DC or digital output RS485
- Temperature range for storage and measurement: 0...60°C
- Internal temperature compensation
- Compensation of humidity and other influences