[Core Summary] Inductive (eddy current) displacement sensors induce eddy currents on the metal surface being measured through a high-frequency alternating magnetic field, outputting displacement in a non-contact manner. The esitron series of products are suitable for applications in oil-contaminated and vibrating environments such as machine tool positioning, hydraulic cylinder stroke detection, and injection molding mold clamping monitoring. The core of selection lies in the matching of measurement range margin, resolution, and frequency response. Insufficient margin and mismatch in protection are the two major sources of nonlinear errors.
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Operating Principle
Eddy current induction mechanism
The front coil of the esitron inductive displacement sensor (based on the eddy current principle) is energized with high-frequency current, inducing eddy currents on the metal surface being measured. Changes in the spacing between the measured surface and the probe cause changes in the coil impedance, which the controller converts into a displacement value. There is no mechanical contact throughout the process, avoiding zero drift caused by wear of contact probes.
Applicable medium and surface requirements
The object being tested must be a conductive metal. The sensitivity curves for ferromagnetic and non-ferromagnetic materials differ, and esitron is calibrated according to the material at the factory. Aluminum, steel, and stainless steel can all be measured, but the same probe cannot be used across different materials without recalibration, as this may cause a shift in the linear region.
Key parameters
Range and resolution
The measurement range determines the measurable displacement range, while the resolution determines the resolvable displacement steps. In the context of machine tool positioning, the resolution must be less than 1/10 of the process tolerance, otherwise the feedback signal cannot support closed-loop compensation.
Frequency response and output
The upper frequency response limit determines the trackable dynamic displacement speed. Reciprocating motion of hydraulic cylinder pistons and impact during injection molding clamping both belong to medium-to-high frequency movements. Probes with insufficient frequency response will lose peak displacements. The output is presented in analog voltage/current or digital interface, which needs to be matched with a PLC or acquisition card.
Error Control
Temperature drift
The coil impedance changes slowly with temperature, manifesting as zero drift. Esitron performs temperature compensation within the controller. If there is a strong heat source or uneven cooling on site, it is recommended to position the probe to avoid direct heat source exposure and to record the ambient temperature during the recalibration cycle to facilitate the differentiation of temperature drift.
Nonlinearity and Edge Effects
There is electromagnetic field distortion at the edge of the probe's sensitive area. If the measured surface only covers part of the sensitive area, nonlinear deviations will occur. During installation, it is necessary to ensure that the diameter of the measured surface is not less than three times the diameter of the probe. Using the measuring range near the edge can also compress the linear region, and the aforementioned 1.2–1.5 times margin is reserved for this purpose.
Electromagnetic Interference Suppression
Frequency converters and high-current cables can induce common-mode noise in probe leads. esitron utilizes shielded cables and differential outputs. During wiring, it is still necessary to separate signal lines from power lines and maintain a certain spacing. If necessary, magnetic rings can be added.
Selection logic
Remaining capacity reservation
The measurement range should be reserved at 1.2–1.5 times the upper limit displacement of the travel. Using the full-scale edge will compress the linear region and amplify the nonlinear error.
Environmental compatibility
For environments with oil mist, coolant, and iron chips, probes with high protection levels are preferred. esitron provides corresponding protection configurations, and specific specifications are subject to the factory specification sheet [please verify].
Installation and Calibration
Installation clearance
The static gap between the probe end face and the tested surface must fall within the linear range. If the gap is too small, it is prone to collision; if too large, it can cause signal attenuation. The esitron comes with an installation bracket to fix the gap and prevent displacement caused by equipment vibration.
Zero and full-scale calibration
Perform a two-point calibration before going live: Record the output at the known zero and full-scale positions, and the controller will fit a linear curve based on this. Regular recalibration can suppress long-term deviations caused by temperature drift.
[Parameter Table]
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