Factors Affecting the Accuracy of Coating Thickness Gauges

Factors Affecting the Accuracy of Coating Thickness Gauges

The most common coating thickness gauges are based on the magnetic induction method and the eddy current method. The measurement accuracy of the instrument has always been a major concern for users. However, the accuracy of these instruments can be influenced by multiple factors. In addition to the measurement technology itself, accuracy may also be affected by human factors, environmental conditions, and other external influences.

So, what are the specific factors that affect the measurement accuracy of coating thickness gauges?

一:Human-Controlled Factors

1. Curvature
The curvature of the specimen affects the measurement. This influence becomes more significant as the radius of curvature decreases. Therefore, measurements taken on the surface of a curved specimen are unreliable. When measuring coating thickness, it is best to choose a flat surface as the measurement point whenever possible.

2.Deformation of the Specimen
The probe may cause deformation of soft coating specimens, making the measured data unreliable. Therefore, for different types of coatings, suitable probe fixtures can be designed to assist with the measurement.

3.Edge Effect
The instrument is sensitive to abrupt changes in the surface shape of the specimen. Therefore, measurements taken near the edges or at inner corners of the specimen are unreliable.

4.Magnetic Field
Strong magnetic fields generated by surrounding electrical equipment can seriously interfere with magnetic coating thickness measurements.

5.Foreign Substances
The instrument is sensitive to foreign substances that hinder close contact between the probe and the coating surface. Therefore, such substances must be removed to ensure direct contact between the probe and the specimen surface.

6.Probe Pressure
The amount of pressure applied when placing the probe on the specimen can affect the measurement readings. Therefore, it is important to maintain consistent pressure.

7.Probe Orientation
The placement of the probe affects the measurement. During measurement, the probe should be kept perpendicular to the surface of the specimen.

二:Natural Factors

1.Magnetic Properties of the Substrate Metal
Magnetic coating thickness measurement is affected by variations in the magnetic properties of the substrate metal (in practice, the variation in the magnetism of low-carbon steel can be considered minor). To avoid the influence of heat treatment and cold working, the instrument should be calibrated using standard samples with the same properties as the substrate metal of the specimen, or by using the specimen itself before coating for calibration.

2.Electrical Properties of the Substrate Metal
The electrical conductivity of the substrate metal affects the measurement, and this conductivity is related to the material composition and heat treatment method. The instrument should be calibrated using standard samples with the same properties as the substrate metal of the specimen.

3.Thickness of the Substrate Metal
Each instrument has a critical thickness for the substrate metal. When the substrate is thicker than this value, the measurement is not affected by the substrate thickness.

4. Surface Roughness
The surface roughness of both the substrate metal and the coating affects the measurement. The greater the roughness, the greater the influence. Rough surfaces can cause both systematic and random errors. To minimize random errors, multiple measurements should be taken at different locations each time. If the substrate metal is rough, the instrument’s zero point must be calibrated on several locations of an uncoated specimen with similar roughness; alternatively, the coating can be removed with a non-corrosive solution to the substrate metal, and then the instrument’s zero point can be calibrated.