The interpretation of pendulum-type inclinometer readings

The conventional method of inclinometer data analysis computes the displacement components in two mutually orthogonal directions separately by using corresponding readings measured in individual directions. It is shown in this note that calculation errors, although insignificant, are induced when this method is used to interpret data measured by pendulum-type inclinometers, which are widely used as probe inclinometers in engineering practice. The inclinometer readings measured in the two directions are correlative, and they are dependent on both the angle of the inclinometer probe axis inclined to the gravity vertical and on the azimuth angle at which the probe movement direction deviates from one of the two directions. The displacement component in each direction can be interpreted more accurately by simultaneously using the tilt angles in both directions measured directly by the inclinometer probe. Relationships between the actual displacement components, the resultant displacement, the azimuth angle, and the tilt angles are derived and verified by laboratory experiments. A refined calculation procedure is proposed for interpreting the pendulum-type inclinometer readings, and the errors induced in the conventional method are analyzed.Key words: deformation, field instrumentation, ground movements, monitoring.