Non-Contact Caliper Measurement Systems on High Speed Packaging Board Lines
Non-contact optical gauges eliminate mechanical board compression on high-speed lines, enabling tighter cross-machine caliper targets and reduced fiber mass.
Eddy Current Sensor
Magnetic Induction
Electromagnetic probes convert changes in local flux density into discrete electrical signals to measure the proximity of conductive materials. An eddy current sensor detects these fluctuations when metallic surfaces pass through an alternating magnetic field. High frequency currents flow through a coil to generate this field, which induces opposing loops of current within the target object.
Deviations in the amplitude or phase of these induced loops signal shifts in the air gap or the thickness of the material. Calibration requires a stable reference surface that shares the conductivity of the production stock.
Operational Precision
Precision in thickness monitoring depends on the alignment of the probe relative to the target surface. Minimal vibration during the passage of paper rolls or film substrates reduces noise in the output signal. Constant contact with conductive coatings can wear the protective ceramic face of the probe over time, altering the standoff distance.
Automated compensation circuits subtract these gradual drift patterns from the active measurement loop. Stable temperature environments prevent thermal expansion of the coil assembly, which otherwise introduces errors into the output frequency.
Manufacturing Boundary
Converting lines apply this technology to track metallic foils or conductive inks on non-conductive substrates. A thin conductive layer acts as the primary target while the base web remains transparent to the magnetic field. Measurement depth stays limited to the skin effect of the material, which restricts accurate readings to the outermost surface layers.
Limitations appear when the conductivity of the material varies across a single batch, as these fluctuations degrade the accuracy of the thickness claim. Signal processing algorithms provide the final output for machine control systems to adjust coating weight or web tension.