Novel monolithic pendulum tiltmeter with Nanorad resolution

Abstract

Abstract Tiltmeters with nanorad resolution in a large measurement range of ±9 mrad (±0.5○) and a very good linearity have been developed at the Technische Universität Ilmenau in the recent years. The working principle bases on the measurement of tilt-dependent lateral forces, which act on a hanging force-compensated weigh cell (precision balance). The disadvantage is the relatively complex design of the weigh cell mechanics, the large dead weight and the high manufacturing costs. For that reason a simplified tiltmeter was developed. It only consists of two components: a monolithic pendulum mechanics and an optical position sensor. State of the art pendulum tiltmeters contain several components that are linked by screwed, clamped or glued connections. This can limit the long-term-, temperature- or humidity stability of the tiltmeter. The position sensor achieves a standard deviation of ∼ 50 pm at a measuring frequency of 10 Hz. The length of the pendulum amounts to 0.1 m, its mass is ∼ 62 g. With this combination, the theoretical standard deviation of the tilt measurement should result to ∼ 0.6 nrad at 10 Hz measuring frequency and was approved by measurements. The measurement range of the new monolithic tiltmeter amounts ∼ ±2 mrad.