What is the working principle of online thickness gauge

Source：www.cshuaqiang.com Release date： 2026-08-18

Online thickness gauges are used in continuous production lines for films, non-woven fabrics, rubber, sheets, lithium battery electrodes, coatings, glass fibers, plastic films, etc. They measure thickness in real-time without interruption and have closed-loop feedback control. There are four common principles, and industrial scenarios are clearly distinguished:
1. β - ray thickness gauge (nuclear radiation thickness measurement, thin film/paper/lithium electrode sheet)
Principle
Using radioactive isotopes to release beta rays (electron flow), when the rays pass through the tested material, a portion of the rays are absorbed by the material.
The radioactive source emits constant intensity beta rays;
The thicker and denser the material, the more radiation it absorbs;
The detector below receives the penetrating radiation and converts it into an electrical signal;
The control system compares the original radiation intensity with the received intensity, and combines it with the material density model to convert the real-time thickness.
Applicable: Paper making, plastic film, positive and negative electrode sheets for lithium batteries, aluminum foil
Characteristics: Belongs to radioactive source equipment and requires compliance filing; Not affected by material color or transparency.
2. X-ray online thickness gauge
Principle
High voltage excitation generates X-rays, which penetrate through the plate/metal strip. The material absorbs the X-rays, and the detector collects the remaining radiation energy.
The thicker the thickness and metal material, the weaker the transmission signal.
Applicable: metal strip, copper foil, aluminum strip, thick plate
Differentiation: Higher energy than beta rays, suitable for metals; High protection requirements.
3. Laser displacement thickness gauge (triangle laser thickness gauge, non-contact, most commonly used)
Divided into dual laser beam type (with two sets of laser heads on top and bottom)
Principle
Based on laser triangulation method
The laser sensor above measures the surface position of the tested material;
The laser sensor below measures the position of the material's lower surface;
The controller calculates the difference between two positions as the material thickness.
Advantages: No radiation, simple installation, easy maintenance
Applicable: rubber, wooden board, plastic board, glass, thick film, roll material
Limitations: Transparent films are prone to measurement errors due to light transmission; Sensitive to surface reflection.
4. Near infrared/optical transmission thickness gauge (infrared thickness gauge, thin film industry)
Principle
Specific wavelength infrared light passes through thin films, and polymer materials absorb specific wavelength infrared light.
The degree of light absorption is directly proportional to the thickness of the film, and the thickness is converted through spectral signals.
Applicable: Transparent plastic film, multi-layer co extruded film
Cannot measure opaque materials.
5. Capacitive online thickness gauge (for a few thin films and coatings)
Principle
The measured medium is placed between two electrode plates, and the capacitance varies with the thickness of the medium. A capacitance thickness conversion model is established.
Mostly used for insulating films, it is easily affected by humidity and temperature interference.

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