JJG 818-2018Magnetic and Eddy Current Measuring Instrument for Coating Thickness (English PDF)

4.1 Measuring force and its variability

The measuring force of the probe of thickness measuring instrument. (0.3~1.5)

N. The variability of measuring force shall not exceed 1/3 F, where F is the average of 10 measured forces.

4.2 Measurement repeatability

The measurement repeatability of thickness measuring instrument shall not exceed the one specified in Table 1.

4.6 Thickness sheet

See Table 1 for the uncertainty and uniformity of the thickness measurement results of thickness sheet.

5.1 Appearance

5.1.1 The designation of thickness measuring instrument shall be marked with instrument name, model, number, manufacturer name (or logo).

5.1.2 The appearance of thickness measuring instrument shall be neat, without obvious scratches, rust, damage, blistering, peeling of paint film. The surface of thickness sheet shall not be severely scratched or damaged.

5.2 Interaction of each part

5.2.1 The pointer movement of the indicator is smooth, without jamming, sticking needles, crawling, etc.

5.2.2 The connection of connectors is reliable and convenient to use. All operation switches, knobs, keys and indicators work reliably and effectively.

Fasteners must not be loose or defective.

5.2.3 The functions of thickness measuring instrument shall work reliably and effectively.

6.1 Verification conditions

6.1.2 Verification equipment

See Table 3 for main verification equipment.

6.2 Verification items and main verification apparatus

See Table 3 for verification items.

6.3 Verification methods

6.3.1 Appearance

Visual observation.

6.3.2 Interaction between each part

Visual observation and manual test.

6.3.5 Indicated value error

Conduct the zero-point adjustment of thickness measuring instrument according to the instructions of use.

6.3.6 Indicated value stability

Select the minimum range stop of the thickness measuring instrument for the

AC-powered thickness measuring instrument. Place a thickness sheet with a value greater than 1/2 of the range near the center of the working surface of the substrate. Mount the probe on the verification table and press it vertically towards the thickness sheet and make it fixed. Record the first reading. Take a reading every 15min later. Continuously record for 1h. Take the difference between the maximum and minimum values in 5 readings as the measurement result.