Initial characteristics of pressure sensors

DONET, i.e., the dense ocean-floor network system for earthquakes and tsunamis has started its operation in the Nankai Trough, SW Japan in the early of 2010. DONET in 20 observatories consists of various geophysical sensors such as broadband seismometer, seismic accelerometer, tsunami meter, and so on. The present study focuses on pressure sensors being used as tsunami meters measuring hydraulic pressure change. Pressure sensors specify their performance for both hysteresis and repeatability, however there is no specification about the long-term sensor´s stability. In this study, we evaluate the initial sensor´s stability in terms of the laboratory experiment and the in-situ measurements. The high accuracy pressure standard is used for the laboratory experiment. The present experiment has been done by applying 20 MPa hydro-static pressure to the pressure sensors, which is equivalent to approximately 2,000 m water depth under the constant temperature of 2 °C for duration of one month. As a result, our experiment suggests that sensor´s drift vary among pressure sensors and the sensor´s drift occurs 10 cm per month in maximum. On the other hand, we evaluate the sensor´s drift since deployment into the deep-sea by removing tide component. The in-situ measurement indicates that the sensor´s drift continues after the deployment. Some pressure sensor´s drift in the initial stage from the in-situ measurement corresponds to that from the experiment for the direction and the rate.