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Application Skills of New Coating Thickness Gauge
Release date: : 2021-04-30 14:49:13
1. Introduction
UT343D is a portable high-accuracy coating thickness gauge, which can measure coating thickness on both ferrous and non-ferrous metal. This device has features of high precision and non-destructive measurement, and functions of single-point, multi-point averaging algorithm and quick judgment. It is widely used in manufacturing, metal processing, marine mechanics, quality supervision, and other industries. Due to its small size and integration of sensor and gauge, the device is especially suitable for on-site measurement.
2. Measuring Principle
Magnetic Induction Principle (FE): Coating thickness is measured by the magnetic flux flowing from the sensor through the non-ferromagnetic coating into the ferromagnetic substrate. It is also possible to measure the corresponding reluctance to indicate the coating thickness. The thicker the coating is, the larger the reluctance and the smaller the magnetic flux.
Eddy Current Principle (NFE): A high-frequency AC signal generates an electromagnetic field in the sensor coil. When the sensor is close to a conductor, an eddy current is formed. The closer the sensor is to the conductive substrate, the larger the eddy current and the greater the reflected impedance. This feedback effect characterizes the distance between the sensor and the conductive substrate, that is, the thickness of the non-conductive coating on the conductive substrate.
Figure 1 shows the measuring principle of the UT343D coating thickness gauge, which mainly includes a sensor, a ferrous substrate (FE) measurement processing circuit, a non-ferrous substrate (NFE) measurement processing circuit, a MCU processor, a display, and operation control and USB communication modules.

Figure 1

3. Key Features
1. Two-point quick calibration of any thickness within the range, which is very convenient and accurate.
2. Gemstone embedding technology is adopted for the sensor, which is characterized by precision, wear resistance and stability.
3. Single-point and multi-point quick judgment functions, which are intuitive and easy to operate.
4. 3-color warning light indicates the current value attribute (green: qualified. red: below the limit. yellow: above the limit).
5. The display of the screen can be automatically rotated and manually locked, so that users can read the measured values from different angles.
6. USB communication function: Online measurement and data upload; data analysis, tendency chart drawing, chart printing, etc.
7. Automatic identification of the substrate.

Application Knowledge and Skills

1. Why Is the Correct Holding Posture Needed?
The reason why the coating thickness gauge is able to measure the thickness of the micron-scale coating is that it can sample small changes in magnetic flux and convert them into digital signals. During measurement, if the user is not familiar with the holding posture of the gauge, it may cause the sensor to deviate from the substrate under test and cause a change in magnetic flux, leading to a measurement deviation.
To obtain better measurement accuracy and exert the best performance of the gauge, the correct holding posture is very important. It directly affects the stability and measurement accuracy of the gauge.
Correct holding posture: Use the thumb and forefinger of the right hand to clench the anti-slip positions of the front and rear housing of the device (see Figure 2), then use a moderate down force to press the device vertically down on the measuring plane of the object under test; Other wrong holding postures (see Figure 3) easily cause jitter of the device, resulting in a deviation in the measurement.

Figure 2    √

Figure 3   ×

2. Why Is It Necessary to Turn On the Device Away From Metal?
For a coating thickness gauge which measures coating thickness based on the Magnetic Induction Principle, when a magnetic metal object is close to the measuring end face of the working sensor, the magnetic induction measured by the sensor will be affected, thereby affecting the measurement accuracy.
UT343D coating thickness gauge initializes the reset value each time it is turned on. If a magnetic metal object is close to the measuring end face of the sensor in this process, the device will regard the measurement parameter corresponding to the metal object as the reset value by default and store it in the system.
When coating thickness is measured under the above conditions, negative phenomena such as no response or incorrect measurement may occur. Therefore, please remove the magnetic metal object when turning on the device and use it after initialization.
If you accidentally use the device under the above conditions, please turn off the device and restart it in an environment where no magnetic metal is close to the sensor.
Figure 4 is the correct boot image (away from metal) while Figure 5 is the wrong boot image (near metal).

Figure 4    √

Figure 5   ×

3. Why is Calibration Required Before Use?
Changes in the environment (such as changes in temperature, humidity, altitude and intensity of the surrounding electromagnetic field) may cause measurement error.
Someone has done a simple experiment. When the device is working near an electromagnetic field of about 10,000 volts, the measurement will be seriously disturbed. If it is very close to the electromagnetic field, there may be a crash.
Physical changes in the device (adhering substances, device drops, etc.) may also cause measurement error.
If the device encounters physical changes such as drops and strong vibrations, it needs to be recalibrated before use.
The device is sensitive to adhering substances that impede the sensor's close contact with the coating surface, so it should be used after removing the adhering substances and recalibration. 
Therefore, the device needs to be calibrated before use to correct measurement error caused by environmental and physical changes.
UT343D coating thickness gauge uses two-point quick calibration to correct measurement error caused by environmental and physical changes, which is more efficient, convenient, and accurate than the existing multi-point calibration method, providing users with a new measurement experience.
For the specific calibration procedure, please refer to the two-point calibration part in Calibration of the Gauge of the UT343D Coating Thickness Gauge User Manual (see Figure 6).

Figure 6

4. How to Choose the Correct Calibration Substrate?
Generally, a coating thickness gauge is shipped with a set of calibration substrate, which includes one ferrous (FE) substrate and one non-ferrous (NFE) substrate (see Figure 7), so that users can use it as a reference substrate in the absence of measuring substrate. In principle, if there is a measuring substrate, it should be chosen as the calibration substrate for pre-use calibration. The reasons are as follows:
For a coating thickness gauge based on the Magnetic Induction Principle, the material and physical dimensions (such as thickness, size, etc.) of the metal substrate will affect the magnetic induction measured by the sensor, thereby affecting the measurement accuracy. If the reference substrate is used as the calibration substrate, the measurement results may differ somewhat, because the reference substrate and the actual measuring substrate are likely to have material or physical differences.

Figure 7