Monday, October 30, 2006

Gravity Based Inclinometer Technology: Liquid Capacitive Basics

Liquid Capacitive Gravity Based Inclinometer Basics:

The sensing element of Rieker inclinometers use liquid capacitive technology, which is based on gravity. The best way to understand how they work is to think of a disc-like cavity that is half filled with a dielectric liquid. One of the sides of the cavity has an etched conductor plate that is used to form one of the conductors of a variable parallel plate capacitor. The liquid along with the other side of the cavity forms the other plate of the capacitor. In operation, the sensor is mounted so that the disc is positioned perpendicular to the ground (vertically mounted). Gravity then acts on the liquid pulling it down in the cavity forming a semi-circle. As the sensor is rotated the liquid remains in this semi-circular pattern covering a different area of the etched plate. This change in area results in a change in the capacitance. The change in capacitance is then electronically converted into an output signal that is linear with respect to in the input angle.

The liquid capacitive technology also has a very low-frequency response bandwidth's - typically 3Hz - which means that their response times are much slower than most spring mass based inclinometers, around 250mSeconds. The benefit of these small bandwidths helps to dampen spikes in the output in applications with lots of vibrations and shock. The inclinometers are made with extremely tight cavities to provide even more damping, compared to other liquid based units where the liquid is known to "slosh" around. All Rieker units are completed encapsulated providing shock and vibration protection. They contain no moving mechanical parts. Only the liquid is free to move making them extremely rugged for harsh environments. This design offers shock protection in excess of 10,000g. Some have built in filtering or come in metal boxes with additional capabilities (SB1i or SB1U).
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