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Direct and inverted pendulums

Hanging pendulums are designed to monitor horizontal movements. They are very commonly utilized in concrete dams to measure change of verticality of the structure.

The direct pendulum is a gravity-referenced instrument. It consists of a steel wire anchored at a fixed point and a damping tank containing damping fluid.

The inverted pendulum provides a fixed datum from which structural movements can be measured. It utilizes the identical wire anchored in borehole beneath the structure, with a floating unit fixed to its upper end. The floating unit is free to move in a fluid tank, keeping the wire vertically suspended.

Pendulums are often installed in shafts in the concrete of the dam starting with an inverted pendulum anchored in foundation to obtain a complete profile of the change in the verticality of the dam.

Direct pendulum assembly includes:
-    Stainless steel cylindrical fluid tank with cover
-    Wire tensioning weight and damping unit
-    Upper wire anchor system with rail and sliding block
-    Turnbuckle for trimming the damping unit position
Tank dimensions 415mm diam, 476 mm high
Material stainless steel
Damping fluid (mineral oil) SAE 50-90 (not supplied)

Inverted pendulum assembly includes:
-    Stainless steel anular chamber with cover
-    Stainless steel floating unit
-    Adjustable tie bar with 100mm vertical stroke
-    External tube liquid level survey
-    Steel ballast for borehole wire anchoring
Tank dimensions 615mm, 495mm high
Floating unit allows ±72mm movement in any direction
Groutable anchor diameter 75mm, adjustable from 80mm to 160mm by centralized pins
Material stainless steel. 

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