What Is an Extensometer?

Extensometer is an instrument for measuring the line deformation between two points of components and other objects. It usually consists of three parts: sensor, amplifier and recorder.

Chinese name: Extensometer
Foreign name: extensometer

Brief introduction: An instrument
Make up: Consists of sensors, amplifiers and recorders

Extensometer principle

The sensor is in direct contact with the component under test. The distance l between the two points measured on the component is the gauge distance, and the change in gauge distance l (elongation or contraction) is the line deformation. The component is deformed, and the sensor is deformed, and this deformation is converted into mechanical, optical, electrical, acoustic and other information. The amplifier amplifies the tiny signal output by the sensor. The recorder (or reader) directly displays or automatically records the amplified signal. ^[1]

Extensometer classification

Extensometer Overview

There are many types of extensometers, which can be roughly divided into mechanical extensometers, optical extensometers, and electromagnetic extensometers. These extensometers typically have a sensitivity of 1 micron. The following are some representative extensometers:

Extensometer Table Type Extensometer

The deformation in the gauge range can be amplified by the dial magnification system's top dial to the gear magnification system inside the watch, and then read out by the pointer on the dial (Figure 1). Its sensitivity depends on the sensitivity of the dial gauge.

Figure 1 Dial indicator principle diagram

Extensometer Extensometer

This extensometer uses a compound lever to magnify, with a magnification of approximately 1,000. Its gauge length can be selected. This extensometer can be fixed to the component to measure the deformation of the component. It has high sensitivity and adaptability (Figure 2).

Figure 2 Tie rod extensometer

Extensometer Martin

The deformation is enlarged according to the principle of the optical lever. When the component is deformed, the movable contact point moves, so that the mirror mounted on the movable edge is rotated (Figure 3). At this time, the data on the scale can be read from the telescope in the instrument. Magnification

. In general, the deformation is small, so that is very small, so the magnification can be written as

. Changing the distance from the mirror to the ruler can change the magnification. After modifying the stand of this instrument, it can also be used to measure the corner of the surface of the component. When the deformation is large, the rotation angle of the deformation and the support is not proportional. This is a disadvantage of this instrument.

Figure 3 Schematic diagram of Martin instrument

Extensometer Capacitive Type

The change in the length of the object is converted into the change in capacitance, and the measured change in capacitance is converted into the strain of the object. Because it basically has no hysteresis at high frequencies, it can be used for dynamic load testing, such as the determination of impact force (Figure 4).

Figure 4 Capacitive Extensometer

Extensometer Inductive Extensometer

Due to the deformation of the component, the core moves, which causes the coil inductance to change. As a result, a voltage is generated in the output coil. By amplifying and measuring this voltage, the law of displacement and movement of the component can be converted. It is not as lightweight as a resistive extensometer, but because it has better stability during long-term measurements, it is suitable for standing measurement devices (Figure 5).

Figure 5 Inductive Extensometer