Application notes for the coating thickness gauge UT343D

1. Introduction

The UT343D is a portable, highly accurate coating thickness gauge that can measure the thickness of coatings on both ferrous and non-ferrous metals.

This instrument has high-precision and non-destructive measurement functions, as well as a single-point and multi-point averaging algorithm and a fast output of the measurement result for evaluation. It can therefore be used in production, metal processing, aerospace, ship mechanics, rail transport, scientific research, quality control and other industries. Due to its small size and the integration of the sensor into the measuring device, the device is particularly suitable for mobile measurements.

2. Measuring principle

The eddy current principle is used for non-ferrous metals (NFE): a high-frequency alternating current signal generates an electromagnetic field in the sensor coil. If the sensor is near a conductor, an eddy current is formed. The closer the sensor is to the conductive background, the greater the eddy current and the greater the reflected impedance. This feedback effect characterizes the distance between the sensor and the conductive substrate, i.e. the thickness of the non-conductive coating on the conductive substrate.

Figure 1 shows the structure of the UT343D coating thickness gauge, which consists of a sensor, a measuring and processing circuit for ferrous metals (FE), a measuring and processing circuit for non-ferrous metals (NFE), a microprocessor (MCU) that evaluates the measured data, a display, control elements and a USB communication interface:

3. Main features

1. Practical and fast two-point fast calibration
2. Advanced sensor technology, which is characterized by precision, wear-resistance and stability
3. Single-point and multi-point quick assessment functions that are intuitive and easy to use.
4. The three-coloured warning light clearly indicates the current measurement result (green: within tolerance. Red: below the limit value. Yellow: above the limit value).
5. The screen display can be automatically rotated 90 degrees 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, draw trend chart, print chart etc.
7. Automatic identification of the surface

Application notes

1. The correct position of the device during measurement

The reason why the coating thickness gauge can measure coating thickness in the micrometer range is that it can sense very small changes in magnetic flux and convert them into digital signals. If the user is unfamiliar with the holding position of the meter during measurement, the sensor may lose full-surface contact with the substrate under test and the magnetic flux may change, resulting in a measurement error and therefore an erroneous display.

In order to achieve better measurement accuracy and to get the best performance from the encoder, the correct holding position is very important. This has a direct effect on the stability and measuring accuracy of the measuring device.

Correct positioning: With the thumb and index finger of the right hand, grasp the rubberized gripping surfaces of the front and rear housing of the device (see Figure 2) and then place the device vertically on the measuring point of the test sample with moderate force. Other incorrect holding positions (see Figure 3) will quickly cause an unclean scanning position of the device, resulting in measurement deviation and measurement errors.

2. Why must the device not be switched on near metal objects?

In a coating thickness gauge that measures the coating thickness according to the principle of magnetic induction, the magnetic induction measured by the sensor affects the measuring accuracy when a magnetic metal object is near the measuring surface of the sensor.

The UT343D coating thickness gauge initializes the reset value each time it is switched on. If a magnetic metal object is located near the measuring surface of the sensor, the device considers the measuring parameter corresponding to the metal object as a default reset value and stores it in the system.

If the coating thickness is then measured under the above conditions, negative phenomena such as no reaction or incorrect measured values may occur. Therefore, only switch on the device when there are no metallic objects near the sensor. Do not approach a metal surface until after the self-test.

If you accidentally use the unit under the above conditions, turn it off and restart it in an environment where there is no magnetic metal near the sensor.

Figure 4 shows the correct start indication (away from metal), while Figure 5 shows the warning if a metal object is too close.

3. Why is calibration necessary before use?

Changes in the environment (e.g. changes in temperature, humidity, altitude and intensity of surrounding electromagnetic fields) can lead to measurement errors.

If the device works under the influence of a strong electromagnetic field, the measurement is massively disturbed, in extreme cases the system may crash.

Physical influences such as adhering substances that hinder the contact of the sensor with the measuring surface, shocks, falling, strong vibrations etc. can also lead to measuring errors. Therefore, the device must be recalibrated before each use.

The UT343D coating thickness gauge uses a two-point fast calibration to correct measurement errors caused by environmental and physical changes. This is more efficient, practical and accurate than the often used multi-point calibration method and provides more accurate measurement results.

For information on the specific calibration procedure, refer to the two-point calibration section of the UT343D Coating Thickness Gauge Operating Manual (see Figure 6).

4. How to choose the right calibration material?

In general, a coating thickness gauge is supplied with a set of calibration materials containing a ferrous (FE) substrate and a non-ferrous (NFE) substrate (see Figure 7) so that the user can use it as a reference material if no other reference is available.

If the surface material to be measured is available with and without coating as calibration material, this should always be used for calibration before use.

The reasons are as follows:
In a coating thickness gauge based on the principle of magnetic induction, the material and physical dimensions (such as thickness, size, etc.) of the metal substrate influence the magnetic induction measured by the sensor and thus the accuracy of the measurement.
If the reference material supplied is used for calibration, the measurement results may differ slightly, since the reference material and the actual material to be measured usually have material or physical differences.