A review of traditional and new methods applicable for the calibration of high resolution tilt sensors

Since the 1960s, the Institute of Earth Physics and Space Science (EPSS) in Sopron has been using different types of tiltmeters with nanoradian sensitivity to observe geodynamic phenomena (e.g. tides). In principle, the high sensitivity and the long term mechanical stability of the recently developed sensors (e.g. Lippmann-type tiltmeters) make it possible to detect rock tilts related to small seismo-tectonic deformations. On this research field the extensive use of networks of these devices is expected in the future. For the correct comparision of tilt values measured by different sensors, the instruments must be calibrated by suitable devices realizing simple and standardized metrological principles. Due to the high sensitivity of Lippmann tiltmeters, traditional comparators (e.g. level balances) can only be used to determine the sensors' characteristics on average over the entire measurement range. In the range below microradian theoretically the Newtonian (gravitational) method can be used to test the capabilities of the tilt sensors. The poster on the one hand shows the Lippmann tiltmeters and level balance joint measurement results. On the other hand the modell computation are discussed, which shows that the off-axis variation of the gravitational vector generated by the vertical movement of the cylindrical ring mass of the Mátyáshegy moving mass calibration device can provide for calibration a sufficiently accurate reference signal having (15±0.02) nrad peak-to-peak amplitude. It is just in the range of tilt induced by earth tide effect, which is a “standard” signal component in the time series recorded in observatory environment.