Analog displacement sensor

A measuring element that converts the measured displacement into an analog signal output. It is usually composed of transforming elements, guide members and measuring force springs, and sometimes the sensor also includes a part of the measuring circuit. Analog displacement sensors can be divided into resistive, capacitive, inductive, eddy current, photoelectric, and Hall type according to the working principle of the transforming element. The figure is a schematic diagram of the structure of an inductive displacement sensor. The conversion element is mainly a differential inductive coil composed of a coil and a magnetic core. When measuring the displacement, the measuring end of the sensor is in contact with the measured object, the measuring end feels the displacement S, and the magnetic core is moved correspondingly through the measuring rod, which changes the inductance of the coil and sends out a signal. After the measuring circuit converts and amplifies the sensor output signal, the indicator indicates the measured displacement value. The movement direction of the magnetic core is restricted by the sliding fit of the measuring rod and the housing. The measuring force spring gives the measuring force required to keep the measuring end in contact with the measured object during measurement. The analog displacement sensor has a simpler structure and lower price, so it has a wide range of applications. The upper limit of measurement is 130 microns to 625 mm, and the measurement error is 0.01 to 2%.

Digital displacement sensor

The measuring element that converts the measured displacement into a digital signal output, also known as an encoder. Encoders are classified into absolute encoders and incremental encoders according to their encoding methods.

Absolute encoder

It can generate a unique digital code corresponding to each displacement, so when indicating a certain displacement, the encoder does not need to store the original displacement. The resolution of the code depends on the number of digits output by the encoder. The structure of the encoder is related to the change of the physical phenomenon (electricity, light or magnetism) used. For example, a brush encoder is generally a plate on which there are several concentric tracks, called several tracks. The conductive area and some insulating areas on the number of channels constitute a code, and each number of channels corresponds to one digit of the output number. When the plate rotates with the measured object, the electric brush reads the conductive and insulating areas on each track in an electrical contact mode, and generates a digital code. The structure of the magnetic encoder and the optical encoder is similar to that of the brush encoder, except that the encoding output of the displacement is represented by magnetism or light beam. The characteristic of the absolute encoder is that the error will not accumulate, and there is no need to consider the response of the circuit when the displacement changes rapidly.

Incremental encoder

It can generate a jump in current or voltage when measuring the displacement of an object. The displacement increment corresponding to each jump of the output signal is determined by the resolution of the encoder. In order to measure the displacement, the memory must be used to count the number of transitions. Inductosyn, magnetic grids and gratings belong to this category of sensors. The characteristic of the incremental encoder is that the zero point can be set arbitrarily, and the resolution is 1 micron.
The digital displacement sensor has high measurement accuracy and wide measurement range. It is suitable for the measurement of large displacements and is widely used in precision positioning systems and precision processing technologies.