TURTLE
TOUGH
®
9
Calibration
Calibration Verification Check
Every instrument leaves our manufacturing facility in a calibrated condition after going through a test programme
of several hours. The user should nevertheless re-check the calibration since a change may have occurred due to
long transport or storage periods.
For a fast routine check it is sufficient to have the sensor in atmospheric air. The air calibration table on the front
panel of your instrument shows the appropriate oxygen calibration value per degree Celsius.
For example:
20 °C equals 9.7 mg/l O₂ or 21 °C equals 9.5 mg/l.
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If the liquid-crystal display of the instrument indicates, for example a temperature of 20.5°C, the changeover
to oxygen should produce the reading 9.6 mg/l O₂. This is the arithmetic mean between the values 20 °C
(9.7 mg/l O₂) and 21 °C (9.5 mg/l O₂).
•
If the value displayed does not correspond to the value on the table or to the calculated value, it will be
necessary to recalibrate using the calibration potentiometer by means of the screwdriver included.
•
If the setting is correct, the device is ready for carrying out measurement.
Calibration in Atmospheric Air
The 1-point calibration in atmospheric ambient air is the simplest type of calibration. The front panel of the
instrument incorporates the calibration table for air calibration.
1. Put the sensor in a shaded place (avoid direct sunlight). The tip of the sensor and the membrane have to be
dry - remove any humidity by dabbing the tip with tissue paper. Cover the sensor i.e. with newspaper to
avoid any wind on the tip.
2. Wait for at least 15-20 minutes to be sure that the sensor has reached ambient temperature.
3. After determining the air temperature please read the associated calibration value on the air calibration table.
Switch over to O₂ and calibrate using the calibration potentiometer by means of the screwdriver included.
Note:
For high accuracy calibration of your instrument, barometric pressure should be taken into consideration.
Calibration to Barometric Pressure
Different air pressures result in different calibration values, so for high accuracy readings a calibration of your
instrument taking barometric pressure into consideration must be performed. If you know the pressure for your
location you can correct the calibration value according to the following formula:
Corrected calibration value [ppm] = Pressure" [mbar ] x Table calibration value [ppm] / 1013 [mbar]
This is clarified further by the following example:
You have measured a temperature of 20 °C. The air calibration table states the relevant calibration value of 9.7 ppm.
If the environment has a different pressure than 1013 mbar, the calibration value has to be corrected. For example
if we are at 1500m above sea level then the pressure per the pressure table (shown above) equates to 838 mbar.
Then the corrected calibration value would be as follows:
838 x 9.7 /1013 = 8.0
After determining the correct calibration value, set the calibration potentiometer accordingly by means of the
screwdriver included.
