Techniques for resolving typical issues with coating thickness gauges
A thickness gauge is actually an instrument used to check the thickness of an object. It is widely used in industrial production thickness measurement. This type of coating thickness gauge can be roughly divided into the following types according to the different measurement methods: radioactive thickness gauges that use the penetration characteristics of α-rays, β-rays, and y-rays; ultrasonic thickness gauges that use ultrasonic frequency changes And the eddy current thickness gauge using the eddy current principle; there are also capacitive thickness gauges, etc.
In addition, the use of microwave and laser technology to make a thickness gauge is still in the period of research and development and testing. The coating thickness gauge can measure the thickness of non-magnetic coatings (such as aluminum, chromium, copper, enamel, rubber, paint, etc.) on magnetic metal substrates (such as steel, iron, alloy and hard magnetic steel, etc.) and non-magnetic metal substrates Thickness of non-conductive coating (eg enamel, rubber, paint, plastic, etc.) on (eg copper, aluminum, zinc, tin, etc.). It can be used not only for fine measurement in the laboratory, but also for engineering sites. It is widely used in metal manufacturing, chemical industry, aerospace, scientific research and development, etc. It is an indispensable inspection instrument for enterprises to ensure product quality, business inspection and control. .
ONE, working principle The film thickness meter adopts two thickness measuring methods of magnetic and eddy current, which can non-destructively measure the thickness of the non-magnetic coating (such as aluminum, chromium, etc.) on the magnetic metal substrate (such as steel, iron, alloy and hard magnetic steel, etc.) , copper, enamel, rubber, paint, etc.) and the thickness of non-conductive coatings (such as: enamel, rubber, paint, plastic, etc.) on non-magnetic metal substrates (such as copper, aluminum, zinc, tin, etc.).
a) Magnetic method (type F measuring head)
When the measuring head is in contact with the covering layer, the measuring head and the magnetic metal substrate form a closed magnetic circuit. Due to the existence of the non-magnetic covering layer, the reluctance of the magnetic circuit changes, and the thickness of the covering layer can be derived by measuring the change.
b) Eddy current method (type N measuring head)
Use high-frequency alternating current to generate an electromagnetic field in the coil. When the measuring head is in contact with the covering layer, an eddy current is generated on the metal substrate, and a feedback effect is generated on the coil in the measuring head. The covering layer can be derived by measuring the magnitude of the feedback effect thickness of.
TWO, common faults and troubleshooting methods The faults of the coating thickness gauge mainly include unstable display, large measurement errors, and no data displayed on the screen. The factors that lead to these failures come from the instrument itself, the factors of the workpiece under test, and the influence of human beings. Let's introduce the methods to eliminate these failures.
1. The display value is unstable
The factors that lead to the unstable display of the coating thickness gauge mainly come from the particularity of the material and structure of the workpiece itself, such as whether the workpiece itself is a magnetic material. If it is a magnetic material, we must choose a magnetic coating thickness measurement Instrument, if the workpiece is a conductor, we have to choose an eddy current coating thickness gauge. Furthermore, the surface roughness and attachments of the measured piece are also important factors that cause the instrument to display unstable values. The probe of the thickness gauge is extremely sensitive to those attachments that prevent close contact with the surface of the covering layer. It is necessary to ensure that the probe is in direct contact with the surface of the coating. Therefore, the key to eliminating this kind of fault is: remove the dust, fines, grease and corrosion products and other attachments on the contact surface of the tested part before measurement, but do not remove any covering material. In addition, when the system is zeroed, the surface of the substrate used must also be cleaned and lubricated. If you feel that the error of the measurement result is relatively large, please use the plastic calibration sheet equipped with the instrument to do a round of testing first. If the deviation is far from the allowable error, there may be a problem with the instrument itself, and it needs to be returned to the manufacturer for repair. The appropriate matrix was not selected during system calibration. The base facet is 7mm, and the minimum thickness is 0.2mm. Measurements below this critical condition are unreliable.
2. The screen does not display data
The simple factor is to check whether the battery power is sufficient. After confirming that the battery power is sufficient, if the measurement still does not display the value, you can consider whether the probe and the connection are loose, disconnected or have poor contact, and the battery is corroded after leakage. Influenced by factors such as electronic components in the instrument. In actual work, the editor has encountered the phenomenon that the probe is corroded by chemicals due to improper use, resulting in the instrument not displaying data.
3. The instrument itself fails
Thickness gauges that have been in the working state for a long time are very likely to have shocks, falls, and other accidents, or the working environment has magnetic field interference, which will cause interference and damage to the electronic components inside the instrument. , resulting in unreliable measurement data of the instrument, garbled data display on the screen, and even inability to start the machine, etc. Therefore, it is recommended to ensure that the instrument is used and kept by a special person as much as possible, and returned to the factory for repair in time when a fault occurs, and it is not allowed to disassemble the machine for inspection without authorization.
Therefore, when using the thickness gauge to measure, pay attention to the following points:
(1) When measuring, pay attention to keeping the side head straight with the test surface.
(2) Keep the pressure stable during measurement, otherwise the measurement reading will be affected.
(3) When conducting the test, it should be noted that the metal magnetism and surface roughness of the standard sheet substrate should be similar to the test piece.
(4) When measuring, pay attention to the influence of the curvature of the specimen on the measurement. Therefore, it is unreliable to measure on the surface of the curved test piece.
(5) Before measuring, pay attention to whether other electrical equipment around will generate a magnetic field. If so, it will interfere with the thickness gauge of the magnetic thickness measurement method.
(6) Pay attention to the critical thickness of the base metal when performing the test. If it is greater than this thickness, the measurement will not be affected by the thickness of the base metal.
