Magnetic attraction measurement principle
The suction force between the permanent magnet (probe) and the magnetically permeable steel is proportional to the distance between the two, which is the thickness of the coating. Using this principle to make a Thickness Gauge, as long as the difference between the permeability of the coating and the substrate is large enough, it can be measured. Since most industrial products are stamped with structural steel and hot-rolled cold-rolled steel sheets, magnetic Thickness Gauges are the most widely used. The basic structure of the Thickness Gauge consists of magnetic steel, relay spring, ruler and self-stop mechanism. After the magnet is drawn in with the measured object, the measuring spring is gradually elongated and the tensile force is gradually increased. When the tensile force is just greater than the suction force, record the tensile force at the moment when the magnet is separated to obtain the coating thickness. New products can automatically complete this recording process. Different models have different ranges and applicable occasions.
Features and uses:
This instrument is characterized by easy operation, rugged and durable, no power supply, no calibration required before measurement, and low price, which is very suitable for on-site quality control in workshops.
Magnetic induction measurement principle
When the principle of magnetic induction is used, the thickness of the coating is determined by the size of the magnetic flux flowing into the ferromagnetic substrate from the probe through the non-ferromagnetic coating. The corresponding magnetoresistance can also be measured to indicate the thickness of the coating. The thicker the coating, the greater the magnetoresistance and the smaller the magnetic flux. Thickness gauges using the principle of magnetic induction can, in principle, have the thickness of the non-magnetic conductive coating on the magnetically conductive substrate. Generally, the magnetic permeability of the substrate is required to be above 500. If the coating material is also magnetic, the difference in permeability from the substrate is required to be large enough (such as nickel plating on steel). When the probe around the coil on the soft core is placed on the sample to be measured, the instrument automatically outputs the test current or test signal. Early products used a pointer type meter to measure the magnitude of the induced electromotive force, and the instrument amplified the signal to indicate the thickness of the coating. In recent years, circuit designs have introduced new technologies such as frequency stabilization, phase locking, and temperature compensation, using magnetoresistance to modulate the measurement signal. The patented integrated circuit is also used, and the microcomputer is introduced, which greatly improves the measurement accuracy and reproducibility (almost an order of magnitude). Modern magnetic induction Thickness Gauges have a resolution of 0.1um, an allowable error of 1%, and a range of 10mm.
Features and uses:
Magnetic principle Thickness Gauge can be used to accurately measure the paint layer on the surface of steel, porcelain, enamel protective layer, plastic, rubber coating, various non-ferrous metal electroplating layers including nickel and chromium, and various anti-corrosion coatings for chemical and petroleum industries.
Eddy current measurement principle
The high-frequency AC signal generates an electromagnetic field in the probe coil, and eddy currents are formed in the probe when the probe is close to the conductor. The closer the probe is to the conductive substrate, the larger the eddy current and the greater the reflection impedance. This feedback action scale indicates the distance between the probe and the conductive substrate, that is, the thickness of the non-conductive coating on the conductive substrate. Since such probes specifically measure the thickness of the coating on non-ferromagnetic metal substrates, they are often referred to as non-magnetic probes. Non-magnetic probes use high-frequency materials as the coil core, such as nickel-platinum alloys or other new materials. Compared with the principle of magnetic induction, the main difference is that the probe is different, the frequency of the signal is different, and the size and scale relationship of the signal are different. Like the magnetic induction Thickness Gauge, the eddy current Thickness Gauge also reaches a high level of resolution of 0.1um, allowable error of 1%, and range of 10mm.
Features and uses:
The Thickness Gauge using the eddy current principle can, in principle, measure the non-conductive coating on all electrical conductors, such as paints, plastic coatings and anodized films on the surfaces of aerospace aircraft, vehicles, home appliances, aluminum alloy doors and windows and other aluminum products. The coating material has a certain conductivity, which can also be measured by calibration, but the ratio of the conductivity between the two is required to be at least 3-5 times different (such as chrome plating on copper). Although the steel matrix is also a conductor, it is more appropriate to use the magnetic principle to measure such tasks
