Folded pendulum tiltmeter

The application of the folded pendulum (FP) as a tiltmeter is proposed and some features of it have been studied both theoretically and experimentally. First, FP could have a quite low resonance frequency due to its mechanical structure. The period of our prototype FP is 6.2 s and the amplification factor is about 100. Second, FP is not sensitive to the environmental temperature variation but seriously affected by the temperature gradient. The experiment with a temperature gradient modulation shows that the static equilibrium position of the FP will change by 2.5 μrad if the temperature difference between the horizontal platform and the base of the FP is 0.1 °C. With a prototype FP, we have observed obvious tilt tides, and the calibration result shows that the resolution of the FP is about 1.2 nrad.