Displacement measurement

Displacement measurement is the measurement of changes in directed distance (displacement). Devices measuring displacement are based on displacement sensors, which can be contacting or non-contacting.^[1] Some displacement sensors are based on displacement transducers,^[2] devices which convert displacement into another form of energy.^[3]

Displacement sensors can be used to indirectly measure a number of other quantities, including deformation, distortion, thermal expansion, thickness (normally through the combination of two sensors), vibration, spindle motion, fluid level, strain and mechanical shock.^[1]

Displacement sensors exist that can measure displacement on the order of nanometers or smaller.^[1]

Application

Displacement receivers can be used to study and observe the stress waves passing through a material after it is struck.^[4] This can be used, for example, to assess fire damage in reinforced concrete.^[4]

Displacement transducers are often used to measure vibration.^[5]

Types

Optical displacement sensors exist, using reflected light to determine distance.^[6]

An ultrasonic displacement sensor is a kind of displacement sensor.^[6] These measure the distance to targets by emitting high-frequency sound waves and measuring the time they take to return.^[6]

Displacement sensors can be made using linear variable differential transformers.^[6]

Strain gauges can be used as the base for small displacement transducers on the order of 0 to 10 mm.^[7]

In music, certain music keyboards can be considered to measure displacement in the sense that they respond to displacement, rather than velocity (as is more commonly the case).^{[citation needed]}

Examples of displacement-responding sensors include the mechanical action of tracker organs, as well as the force-sensing resistors found in music keyboards that had polyphonic aftertouch capability. Polyphonic aftertouch is no longer a feature of presently manufactured keyboards, but certain older models such as the Roland A50 featured a pressure sensing resistor, similar in principle-of-operation to a carbon microphone, in each key.^{[citation needed]}