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Title

     AIR PRESSURE SENSORS

By
O.M.
Date
24 October, 2015
Version
0.1

Installing air pressure sensor inside seismometer vault might be of relevance for monitoring purposes - checking if the vault is pressure proof (seems it's possible to achieve this on new Hopen tank, and perhaps FAUS with the new lid which has gasket, and cable entry will later be made pressure proof)

We also have a combined Humidity/temperature sensor that is next in line for testing. This is related to avoiding condensation problems: If the vault is pressure proof you can only condense the amount of water that was present in the air at the moment the vault was sealed (provided temperature is lowered) and that amounts to very little. A "condensation machine" acts by repeatedly sucking in air with a high degree of humidity, and that cycle need to be interrupted.

In "Treatise on Geophysics, Vol. 1, Deep Earth Seismology" (Elsevier) there is a chapter on instrumentation; on p.47 is a section "Environmental and ambient seismic noise" where the influence of barometric pressure changes is described. Figure 18 shows coherence between barometric pressure and vertical sensor data, stating: "Coherence is rare at frequencies > 4 mHz" (=240s) so we can assume it's not of interest to log pressure data for correction purposes, under any circumstances.

Other information related to correction of seismometer data is given in this article: The Effects of Athmospheric Pressure Changes on Seismic Signals

Test of pressure sensors


We tested Bosch BMP180 air pressure sensor, and compared results to official weather station data collected nearly, at "Geofysen". Sensor break-out board used: https://www.adafruit.com/products/1603

Click to enlarge.

Click to enlarge.

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Page last modified on February 11, 2016, at 09:08 AM
Electronics workshop
Department of Earth Science - University of Bergen
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