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
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
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.