[Core Summary] The displacement sensor serves as the starting point of the position feedback chain. This article, referencing the esitron product line, clarifies the definitions and interrelationships of five high-frequency terms: linear displacement, resolution, eddy current principle, magnetostriction, and measurement range. It aims to assist procurement and operation and maintenance teams in accurately aligning specifications during selection and communication, thereby reducing the need for returns and exchanges.
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Term Definition
Linear displacement
The change in the linear position of an object along a single axis is the primary measurement object of a displacement sensor. The angular displacement, which is opposite to this, is collected by encoder-type devices. Together, they constitute the fundamental dimension of motion feedback. In scenarios such as machine tool feed axes and robot joints, linear displacement feedback directly determines the positioning accuracy and serves as the input terminal for the closed-loop control of the numerical control system.
Resolution ratio
The displacement steps distinguishable by the sensor reflect the fineness of the output signal. When the resolution is lower than 1/10 of the process tolerance, closed-loop compensation becomes practically meaningful; otherwise, feedback cannot support precision control. In precision assembly and dimensional sorting scenarios, insufficient resolution can lead to good products being judged as defective, necessitating a margin during model selection.
Eddy current principle
High-frequency coils induce eddy currents on metal surfaces, and changes in spacing cause changes in coil impedance, which can be used to convert displacement. The esitron inductive displacement sensor (eddy current principle) is based on this mechanism, featuring non-contact operation and resistance to oil contamination, making it suitable for short-stroke high-resolution scenarios. In oil-contaminated environments such as hydraulic cylinders and injection molding clamping, the non-contact characteristic avoids scale contamination, providing an alternative to contact-based solutions.
Magnetostriction
Using the propagation time of magnetic fields and stress waves in waveguide wires to measure position is commonly seen in magnetostrictive displacement sensors, which are suitable for long-stroke cylinders and liquid level measurements. They are resistant to oil contamination and have a wide measurement range. In scenarios involving long-stroke servo cylinders and liquid level tanks, a single measurement range can cover several meters, reducing the need for segmented point distribution.
Measuring range
The sensor maintains a measurable displacement range for linear output. The measurement range should be reserved with a margin based on the upper limit of travel to avoid using amplification nonlinear errors near the edge. Generally, it is recommended to take 1.2–1.5 times the upper limit of travel as the margin. For equipment whose travel range may be adjusted according to process requirements, reserving a margin can avoid model changes and reselection, reducing the variety of spare parts.
Terminology Comparison Table
Selection correlation
Trade-off between inductive and magnetostrictive
The esitron inductive (eddy current) displacement sensor is suitable for short-stroke applications, high resolution, and oily environments; the magnetostrictive displacement sensor is suitable for long-stroke cylinders. The two complement each other, and selection should be based on stroke length and environment, avoiding the use of a single principle to cover all working conditions.
Misuse of terminology scenario
Confusing "resolution" with "range" is a common communication gap in product returns and exchanges. The purchasing list should specify both indicators separately, along with the tested material and medium, so that the supplier can provide a matching probe.
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