Electric levelling instrument - contains two liquid switches which break contact when two reference edges are not exactly horizontal and vertical resp.

摘要

The electric level determines whether or not a plane is horizontal or vertical, using two liquid switches (4). These are so arrangement that their contacts (5) are only connected, via the switch liquid, when the two reference edges (2, 3) of the housing (1) are exactly horizontal and vertical, respectively. The liquid in the switches may be mercury or water with a substance added to increase its conductivity. The contacts (5) may be connected via a battery (6) with a visual indicator (7), or with an acoustic signal device.