Principle of magnetic gravity measurement and thickness gauge
permanent magnet
(probe)
The attractive force of the magnetically permeable steel is proportional to the distance between them,
this
This distance is the thickness of the coating. As long as the difference between the permeability of the coating and the substrate is large enough,
Measurements can be made.
Since most industrial products are formed by stamping structural steel and hot-rolled and cold-rolled steel plates,
Therefore, the magnetic thickness gauge should
The most widely used. The basic structure of the thickness gauge consists of magnetic steel, relay spring, scale and self-stop mechanism. When magnetic steel is attracted to the measured object, it will
The measuring spring is then gradually extended,
The tension is gradually increasing.
When the pulling force is just greater than the suction force,
Record the pull-down of magnetic steel at the moment of separation.
The thickness of the coating can be obtained by force.
New products can automatically complete this recording process.
Different models have different ones.
Measuring range and applicable occasions.
This instrument is characterized by simple operation, durability, no need for power supply, no need for calibration before measurement, and low price, which is very suitable.
Workshop to do on-site quality control.
Two.
Principle of magnetic induction measurement
When the principle of magnetic induction is adopted,
According to the magnitude of the magnetic flux that the probe flows into the ferromagnetic matrix through the non-ferromagnetic coating,
In order to determine the coating
Thickness. The corresponding magnetoresistance can also be measured to indicate the coating thickness. The thicker the coating, the greater the magnetoresistance.
The smaller the pass.
A thickness gauge using the principle of magnetic induction,
In principle, there can be a nonmagnetic coating thickness on the magnetic substrate.
general requirements
The permeability of the substrate is in.
500
Above.
If the coating material is also magnetic,
It is required that the difference from the permeability of the substrate is large enough.
(such as steel)
Nickel plating)
When the probe around the coil wound on the soft core is placed on the test sample,
The instrument automatically outputs test current or test signal.
Early products used pointer instruments,
Measure the magnitude of induced electromotive force,
The instrument amplifies the signal and then displays the coating thickness.
In recent years, circuit design has introduced frequency stability,
Phase lock,
Such as temperature compensation,
Magnetoresistance is used to modulate the measurement signal.
Return mining
Integrated circuits designed with patents,
Introduce microcomputers,
The measurement accuracy and reproducibility have been greatly improved.
(Almost one number at most.
Order of magnitude)
Modern magnetic induction thickness gauge,
Magnetic induction thickness gauge with high resolution.
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Principle of eddy current measurement
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Principle and application of magnetic gravity measurement
Thickness gauge
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Eddy current principle thickness gauge
0. 1 micron
, the allowable error is as high as
1%
, ranging up to
10mm
Magnetic principle thickness gauge can be used to accurately measure paint layer, enamel protective layer, plastic and rubber coating on steel surface.
Electroplated coatings of various non-ferrous metals, including nickel and chromium, and various anti-corrosion coatings in chemical and petroleum industries.
Three.
Principle of eddy current measurement
The high-frequency alternating current signal generates an electromagnetic field in the probe coil,
When the probe is close to the conductor,
In which a vortex is formed.
Probe ionization conduction
The closer the matrix is,
The greater the eddy current,
The greater the reflection impedance.
This feedback action represents the distance between the probe and the conductive matrix.
The size of,
I.e. the thickness of the non-conductive coating on the conductive substrate.
Because this probe is specially used to measure non-ferromagnetic metal substrates.
The thickness of the coating,
Therefore, it is usually called a nonmagnetic probe.
Non-magnetic probe adopts high-frequency material as coil core,
Such as platinum
Nickel alloy or other new materials.
Compared with the principle of magnetic induction,
The main difference is that the probe is different and the signal frequency is different.
Make conspicuous
The relationship between size and scale is different. Like the magnetic induction thickness gauge, the eddy current thickness gauge has reached the resolution.
0. 1 micron
, allowable error
1%
, scope
10mm
High level.
A thickness gauge based on eddy current principle,
In principle, the non-conductor coating on all conductors can be measured.
Such as a spaceship
Paint, plastic coating and anodic oxide film on the surface of aluminum products such as automobiles, household appliances, aluminum alloy doors and windows. cladding material
Has certain conductivity,
It can also be measured by calibration,
However, it is required that the conductivity ratio between them be at least different.
3-5
double；twofold
(such as copper)
Chrome plating). Although the steel matrix is also a conductor, it is more suitable for this kind of task to be measured by magnetic principle.