What Is a Pachymeter?

Thickness gauge (thickness gauge) is a gauge used to measure the thickness of materials and objects. It is commonly used in industrial production to continuously or sample the thickness of products (such as steel plates, steel strips, films, paper, metal foils and other materials).

The thickness gauge can be used to measure the thickness of the rolled plate and strip online, and output it in the form of electrical signals. This signal is sent to the display and automatic thickness control system to achieve automatic thickness control (AGC) of the strip thickness. At present, there are four kinds of thickness gauges: -ray, -ray, x-ray and isotope ray. The placement positions are all on the exit or entrance side of the strip mill. When designing and installing the thickness gauge, it should be as close to the work roll as possible, in order to reduce the lag adjustment time of the plate thickness.

An instrument used to determine the thickness of the material itself or the thickness of the surface coating. The thickness of some components must be measured during manufacturing and maintenance in order to understand the thickness and thickness of the material, the uniformity of each point and the degree of corrosion and wear of the material; sometimes the thickness of the cover layer on the surface of the material is measured to ensure product quality and production safety. According to different measuring principles, there are four commonly used thickness gauges: ultrasound, magnetic, eddy current, and isotope.

The speed of sound of ultrasonic thickness gauges in various media is different, but the speed of sound is constant in the same medium. Ultrasonic wave propagates through the medium and is reflected when it encounters the second medium. The interval time between the transmission and reception of the ultrasonic pulse can be measured, and this interval time can be converted into thickness. This type of thickness gauge is the most widely used in the power industry. It is often used to measure the thickness of boiler drums, heating surface tubes, pipes, etc., and also to check the structural size of the workpiece. Most of these thickness gauges are portable, the volume is similar to that of a small semiconductor radio, and the thickness value display is mostly digital. For steel, the maximum measurement thickness is about 2000 mm, and the accuracy is between ± 0.01 to ± 0.1 mm.

When the magnetic thickness gauge measures the magnetic resistance of various magnetically permeable materials, the measured value will change due to the thickness of the non-magnetically permeable coating on the surface. With this change, the thickness of the cover layer can be measured. It is often used to determine the thickness of aluminum sprayed layers, plastic layers, electroplated layers, phosphating layers, paint layers, etc. on ferromagnetic metal surfaces.

Eddy current thickness gauge When the probe coil carrying high-frequency current is placed on the surface of the metal to be measured, eddy current is generated in the metal due to the high-frequency magnetic field. The magnetic field generated by this eddy current acts on the probe coil and changes its impedance. This amount of change is related to the distance of the probe coil from the metal surface (that is, the thickness of the cover layer), so the thickness of the metal surface cover layer can be indirectly measured according to the change in the probe coil impedance. Commonly used to determine the thickness of the oxide film on aluminum or other insulating coatings on the surface of aluminum and copper.

The isotope thickness gauge uses the principle of different absorption and scattering of radiation by different material thicknesses, and can measure the thickness of metal materials such as thin steel plates, thin copper plates, thin aluminum plates, silicon steel sheets, alloy sheets, rubber sheets, plastic films, and paper. Commonly used isotope rays include gamma rays and beta rays. ^[1]

The test methods of thickness gauges are: magnetic thickness measurement, radiation thickness measurement, electrolytic thickness measurement, eddy current thickness measurement, and ultrasonic thickness measurement.

Measurement considerations:

When testing, please pay attention to the metal magnetism and surface roughness of the standard film should be similar to the test piece.

Keep the side head perpendicular to the surface of the sample during the measurement.

Pay attention to the critical thickness of the base metal when measuring. If it is larger than this thickness, it will not be affected by the thickness of the base metal.

Pay attention to the influence of the curvature of the test piece on the measurement. It is therefore unreliable when measuring on curved specimen surfaces.

Before the measurement, pay attention to whether other electrical equipment around it will generate magnetic field, if it will interfere with the magnetic thickness measurement method.

Be careful not to measure at the inner corner and near the edge of the test piece, because the sudden change of the surface shape of the general thickness gauge test piece is very sensitive.

Keep the pressure constant during the measurement, otherwise it will affect the reading of the measurement.

When testing, pay attention to the direct contact between the instrument's probe and the test piece. Therefore, the ultrasonic thickness gauge should be cleared of the adhering material on the opposite side.

1. The laser thickness gauge is a non-contact dynamic measuring instrument that uses the principle of laser reflection to measure and observe the thickness of the product by measuring and observing the micro-geometry of the surface of the machined part in mechanical manufacturing. It can directly output digital signals to connect with industrial computers, and quickly process data and output deviation values to various industrial equipment.

2. The X-ray thickness gauge uses X-rays to penetrate the material under test, and the changes in the intensity of X-rays are related to the thickness of the material. Cangzhou Oupu measures the thickness of the material. It is a non-contact dynamic measuring instrument. . It takes PLC and industrial computer as the core, collects the calculated data and outputs the target deviation value to the rolling mill thickness control system to achieve the required rolling thickness. Main application industries: sheet metal foil processing in non-ferrous metals, sheet metal processing in the metallurgical industry.

3. Paper thickness gauge: suitable for measuring the thickness of various films, paper, cardboard and other sheet materials below 4mm.

4. Thin film thickness gauge: It is used to determine the thickness of thin films, sheets and other materials. It has a wide measurement range and high measurement accuracy. It has the characteristics of data output, zero setting at any position, metric and inch conversion, and automatic power off.

5. Coating thickness gauge: used to measure the thickness of coatings on ferrous and non-ferrous metal substrates.

6. Ultrasonic thickness gauge: The ultrasonic thickness gauge is based on the principle of ultrasonic pulse reflection to measure the thickness. When the ultrasonic pulse emitted by the probe reaches the material interface through the measured object, the pulse is reflected back to the probe. The propagation time in the material determines the thickness of the measured material. All kinds of materials that can make ultrasonic waves propagate inside them at a constant speed can be measured using this principle. ^[2]