The instrument measures absolute pressure, and below sea level the pressure readings will then include the water and atmospheric pressure. To adjust for this, a pressure offset needs to be selected for offsetting absolute to relative pressure at the deployment site.
The atmospheric pressure usually fluctuates around 10.13 dBar, and 1 dBar is equivalent to the pressure change over 1 m depth in fresh water (so at 1m depth the absolute pressure would be 11.13 dBar). The factory setting is 9.5 dBar. The outcome is that when the instrument is in air, you will see a value of 0.2-0.7 dBar, depending on atmospheric conditions. Be aware that the pressure sensor cannot output negative values. If the pressure sensor output '0' value, the pressure offset might be too high relative to the atmospheric pressure at site. The pressure sensor outputs the absolute pressure value in units of dBar.
How to adjust the pressure offset:
- Obtain the local atmospheric pressure at the deployment site. This can be retrieved from weather services or websites (e.g. this Website)
- Enter this value into the deployment software as the Pressure Offset.
Alternatively, you may choose the "Set Zero Pressure" option in the software. This sets the current pressure reading as the new baseline, effectively zeroing the offset to the current atmospheric conditions.
For a step-by-step guide, refer to the instructional video prepared by our support team.
💡 NOTE: The pressure offset can only be set to a constant. Should a more advanced correction using a atmospheric pressure time series be required, this will need to be done manually.
The below video illustrates the setting of the pressure offset on the example of a Signature.
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