H84.01.6B-04 Betriebsanleitung GMH 5630 Seite 14 von 20
_____________________________________________________ _____________________________________________________________________________
GHM GROUP –Greisinger | GHM Messtechnik GmbH
Hans-Sachs-Str. 26 | 93128 Regenstauf | GERMANY
Phone +49 9402 9383-0 | Fax +49 9402 9383-33
7.1 Correction of Salinity 'SAL'
The higher the salinity (salt content) the lower the solubility of oxygen in water, i.e. although the partial
oxygen pressure is the same, the quantity of oxygen dissolved in water (mg/l) is lower. Therefore,
determination of the oxygen concentration requires entering the salinity of the medium (p.r.t. 'Configuration').
The correction of salinity is based on media on a water basis, whose chemical content is similar to sea water.
The corrections are based on the 'International Oceanographic Tables' (IOT).
7.2 Ambient pressure and measuring depth of the sensor
The pressure at the sensor membrane is important for:
The calculation of the oxygen saturation (% sat).
At air water can get 100 % saturation. Assumed that there are no oxygen consuming processes
(biological degradation, chemical effects) and that there are no oxygen enriching processes (e.g.
excessive ventilation or photosynthesis).
The calculation of oxygen concentration (mg/l or ppm).
The sensor evaluation at calibration.
Therefore it is necessary to compensate the pressure influence via integrated sensor or, like practised with
more primitive instruments via tables and manual input of pressure or elevation above sea level values..
The integrated pressure sensor is permanently measuring the ambient pressure to:
Compensate the pressure for the concentration [mg/l or ppm] or saturation [% Sat O2]
Pressure compensate the calibration.
8 Kalibrierung des Sauerstoffsensors
In order to compensate for ageing of the sensor, the sensor has to be calibrated at regular intervals.
The device is equipped with easy-to-use calibration functions: Standard 1-point calibration, sufficient for the
most applications and special 2 or 3-point calibration, if high accuracy is needed in extreme measuring.
We recommend to calibrate the sensor at least all 7 days, or to get maximum precision, before each
measuring series.
If the electrode was dry for one or more days it has to be 'watered' for at least 30 minutes before carrying out
a new calibration.
Remove protective flask prior to calibration and wipe membrane with a soft piece of cloth.
8.1 Calibration
Calibration takes place in air saturated with water vapour. The GCAL 3610 calibration
container or the storage bottle can be used for this purpose. The membrane of the
electrode must be dry for the calibration. Prior to performing the calibration of the
membrane, dab away water droplets from the membrane with a soft, dry cloth. The following
must be observed when using the storage bottle:
Only insert the electrode far enough into the storage bottle that the membrane does
not come into contact with the water in the bottle.
Unscrew the lid of the storage bottle and only position it so that a small exchange of
air and pressure equalisation can take place
Place the electrode in the calibration container. If necessary, wait until the temperature
has equalised and a stable value has been achieved.
Press the Function key for 4 seconds to open the Calibration menu. The display
shows (AL.
Release the Function key.
The product determines the correct value automatically.
After successful completion of the calibration the assessment of the electrode condition
is displayed briefly in percent. An aged or contaminated electrode, incorrect adjustment
of the pressure, contamination of the platinum electrode or a damaged membrane
can be the cause for a lower evaluation.
If the calibration is not completed successfully an error message is displayed. (AL ERR.
appears in the display See 13 Error and System Messages. Confirm the error
message pressing the Function key. The product restarts and the value of the last successful
calibration is restored.