A tiltmeter, is a type of instrument used to detect any kind of tilt in the structure to which it is attached. Most tiltmeters use an air bubble in a liquid-filled tube, much like a typical carpenter's level, but are equipped with sensitive electronics that can detect even the tiniest change in tilt. They either sound an alarm or transmit the data to a remote monitor or other device. These instruments have a variety of uses from construction to the study of volcanoes. In times past, a tiltmeter was sometimes called an inclinometer, although this term is rarely used today.
With numerous uses in a variety of construction and civil engineering applications, the demand for these instruments has enabled them to evolve along with technology. The earliest tiltmeter was nothing more than a very long pendulum. If the structure or ground on which it was placed tilted, the pendulum would indicate the movement. These instruments were susceptible to false alarms due to air currents, however. A second type of tiltmeter consisted of two identical containers connected by a long tube. The entire assembly was filled partially with water, and any tilt could be detected by measuring the water levels in each container.
Modern versions of the tiltmeter use direct observation or electronics to monitor the movement of a bubble of air in liquid. As the tiltmeter is moved, the bubble shifts position, and electrodes are able to register the change or the bubble may be compared to a visible gauge. This data can be recorded for later study, either internally or remotely by transmission, or monitored in real time. Some modern tiltmeters are very sensitive and are able to detect a change in tilt as small as 1 arc second. An arc second is a measurement of an angle that is equivalent to 1/3,600th of 1 degree.
The most common uses for a tiltmeter are to monitor buildings for tilt due to settling, earthquakes, or nearby construction activity. They are sometimes used for civil engineering projects to make sure that a tunnel or other structure maintains a level course during construction or repair. Dams are often monitored with a tiltmeter to see if they move or shift as the pressure of water behind them builds. Geologists often employ tiltmeters to montitor conditions near volcanoes, as strategically placed tiltmeters can help predict when a volcano may erupt by registering changes in the surface that can indicate a build up of magma, for instance. A tiltmeter can also help to determine the amount of shift in land features after landslides and earthquakes.