Machine Design

Sensor Sense: Inclination and tilt detectors

An inclination or tilt sensor provides angular-tilt information relative to gravitational force. This information can then be used to change the characteristics of the device. For example, tilt sensors inside smartphones rotate the image on the display to keep it right-side-up. More-rugged versions can monitor the angle of the boom on a crane to reduce the possibility of tip over.

Early tilt switches contained a pool of mercury within a sealed capsule. As the capsule tilted end to end, the mercury would flow to the lower side where it would complete the electrical circuit on a pair of contacts located at that end. Contact closure signaled that the tilt sensor had exceeded its maximum tilt angle.

Modern tilt or inclination sensors use microelectromechanical systems (MEMS) technology. A microspring-supported mass is pulled out of its centered position by gravity. Rather than closing an electrical contact, the amount of movement is measured through a series of fingers that act like the plates of a capacitor. The effective capacitance between the fingers changes as they engage and disengage.

Measuring and comparing these capacitance values represents the machine inclination or tilt angle. Often the output used is either single axis or two axes: the X axis measures tilt side to side while the Y axis measures tilt forward and back.

One advantage in modern inclinometers is the additional use of microcontrollers that make possible features not found in older versions. Range scaling and filtering let designers limit the device range and adapt the filtering to the bandwidth needed. Some devices can add logic output signals that trigger at application-defined angular positions or provide CANopen-based network interfaces.

Inclinometer devices available today come in many fixed ranges such as ±15, ±45, and ±90°. Typical MEMS device accuracies are within ±0.5°, though high-accuracy labeled units can reach accuracies better than ±0.1°.

Pepperl+Fuchs supplied information for this column.

© 2012 Penton Media, Inc.

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