CN115291022A

CN115291022A - Quality control method for batch products

Info

Publication number: CN115291022A
Application number: CN202210989504.5A
Authority: CN
Inventors: 吴伟; 吴跃佳
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-01-06
Filing date: 2018-01-06
Publication date: 2022-11-04
Also published as: CN108562807A

Abstract

A quality control method for batch products. The method comprises the following steps: giving an arbitrary line segment; selecting an evaluated batch of products and acquiring a frequency spectrum of the products; comparing the frequency spectrums of any line segment and batch products and observing the fluctuation of the difference value of the two; and if the difference value fluctuation is abnormal, checking whether quality factors except the electromagnetic interference characteristics of the product with the abnormal difference value fluctuation meet the design requirements. The advantages are that: the EMC condition of the product can be quickly evaluated in a production workshop, so that the evaluation cost is saved; each necessary inspection of the product in the production process of the batch product is beneficial to the quality control; the evaluation result not only reflects the EMC condition of the batch products, but also reflects the product quality except the electromagnetic interference characteristic of the products, and a new means is provided for the quality control of the batch products.

Description

Quality control method for batch products

The application is a divisional application with the application date of 2018, month 01 and day 06, the application number of 201810012675.6 and the name of a method for rapidly evaluating the electromagnetic compatibility condition of a product and controlling the quality.

Technical Field

The invention relates to a method for quickly evaluating electromagnetic compatibility of a product, in particular to a method for quickly evaluating electromagnetic compatibility for controlling quality of the product.

Background

The electromagnetic compatibility (EMC) condition of a product is an important part of the product quality. The low EMC condition of the product can reduce the anti-interference capability of the product, thereby reducing the reliability of the product. However, since the EMC test of a product needs to be performed in a shielded room, which is expensive and time-consuming, the evaluation of the EMC performance of the product so far is limited to the type test of the product, i.e. the EMC test is performed on only one sample of the product, and it is assumed that the EMC characteristics of all subsequently produced mass products of the same type are the same as the sample. However, practically, due to variations in components of products, changes in production processes, and the like, the EMC condition of a batch product deviates from that of a sample.

Disclosure of Invention

The invention provides a method for quickly evaluating the electromagnetic compatibility condition of a product for controlling the quality of the product, which can quickly evaluate the EMC condition of each product in a batch of products. Since the electromagnetic interference (EMI) of the product is generated by the circuit of the product and is closely related to the operating condition of the circuit, the method can also be used for quality control of the batch product.

The invention provides a method for quickly evaluating the electromagnetic compatibility condition of a product, which is characterized by comprising the following steps of:

selecting a reference sample and obtaining a frequency spectrum of the reference sample;

selecting an evaluated product and acquiring a frequency spectrum of the evaluated product;

and comparing the frequency spectrums of the reference sample and the evaluation product, and judging the electromagnetic compatibility condition of the evaluation product.

The evaluation method is characterized in that the reference sample and the product to be evaluated belong to the same type of product, and the EMC state of the reference sample is known.

The method for evaluating is characterized in that the obtaining of the frequency spectrum of the reference sample and the obtaining of the frequency spectrum of the product to be evaluated can be realized by collecting the electric waveforms of the same part on the circuits of the reference sample and the product to be evaluated by an electric signal collecting instrument and obtaining the frequency spectrums through mathematical transformation.

The method for evaluating is characterized in that the obtaining of the frequency spectrum of the reference sample and the obtaining of the frequency spectrum of the product to be evaluated can be realized by measuring the same positions on the circuits of the reference sample and the product to be evaluated by using a frequency tester to obtain the frequency spectrums.

The evaluation method is characterized in that the judgment and evaluation of the electromagnetic compatibility condition of the product comprises the following criteria:

（1）

（2）

wherein R is a difference value, f is a certain frequency in the frequency spectrum, se is the frequency spectrum of the product to be evaluated, sr is the frequency spectrum of the reference sample, estatus is the product evaluation result, margin is the product interference, uncertaintiy is the measurement uncertainty, PASS is passed, FAIL is not passed, and UNCERTAIN is UNCERTAIN.

The evaluation method is characterized in that the reference sample is selected and the frequency spectrum of the reference sample is obtained, and the frequency spectrum of the reference sample can be directly replaced by any line segment.

The method and the calculation formulas (1) and (2) are based on the following basic principles:

product A and product B belong to the same type of product, and the EMI level is represented by frequency spectrum

Basic principle 1. Product B has a lower frequency spectrum than product a, and thus if the EMC standard laboratory tests that the frequency spectrum of product a is below the EMI limit lines specified by the EMC standard and thus meets the EMC standard.

Basic principle 2. Under the same environment, the same instrument is used for measuring the product A and the product B at the same test point to obtain frequency spectrums, and even if the environment and the instrument are different from the standard EMC test requirements, the basic principle 1 still holds.

And 3, measuring the product A and the product B at the same test point by using the same instrument under the same environment to obtain frequency spectrums, and calculating the difference value of the frequency spectrums of the product A and the product B to eliminate the influence of environmental interference.

In practical application, a sample with known EMC condition is selected as the product A, a batch product to be evaluated is selected as the product B, and the EMC condition of the batch product can be quickly evaluated according to the steps of the method and the formulas (1) and (2) of the method. Furthermore, as shown in the following embodiment, since the EMI level of the product is related to the operating condition of the product, the method of the present invention can also be used for quality control of mass production.

In production practice, samples with known EMC conditions are sometimes lacking; it is then possible to consider replacing the spectrum of the reference sample by an arbitrary line segment, for example by an interference-limited line of a standard EMC test or a combination of several line segments of different shapes, etc. In this case, when operating according to equations (1) and (2), margin may take any constant. Since all the products in the series to be evaluated are compared with the same arbitrary line segment to calculate the difference, the difference or the maximum value of the difference of all the products in the series to be evaluated should fluctuate in a narrow range under normal conditions, and if the difference of a certain product is obviously beyond the narrow fluctuation range, the product is indicated to be abnormal in operation, and further quality check is needed.

Advantageous effects

Compared with the prior art, the method has the beneficial effects that:

the EMC condition of the product can be quickly evaluated in a production workshop, and compared with a shielding room test of a standard EMC laboratory, the evaluation cost is saved; the rapid evaluation method enables each necessary inspection of products in the production process of batch products to be possible, and is beneficial to EMC quality control of the products; the evaluation result not only reflects the EMC condition of the batch products, but also reflects the product quality, and a new means is provided for the quality control of the batch products.

Drawings

FIG. 1 is a flow chart of the steps of examples 1-3 of the present invention.

FIG. 2 is a diagram of the conducted interference spectrum of a reference sample in example 1 of the present invention.

Fig. 3 is an EMC status evaluation diagram of the batch product in embodiment 1 of the invention.

Fig. 4 is an EMC condition evaluation diagram of a batch product according to embodiment 2 of the present invention.

Detailed Description

The following detailed description of the present invention is provided in connection with the accompanying drawings and examples.

Example 1

In example 1, the mass-produced product is a USB dc charger, one product of the same type as a sample is subjected to a standard EMC laboratory conducted interference test with a test standard of EN61000-6-3 and a frequency range of 150 kHz-30MHz, and the test result is shown in fig. 2. In fig. 2, the distance from the standard line of the amplitude values of different frequency points in the sample spectrum is the EMI margin (margin) of the frequency point. The uncertainty (uncertainties) of the EMC laboratory test for this sample was + -1.66dB. In this case, a digital oscilloscope is used to measure the batch product and the reference sample at the power input end respectively to obtain a voltage signal, and the voltage signal is subjected to FFT conversion to obtain a spectrum Se of the batch product and a spectrum Sr of the reference sample. The difference of the spectrum from the frequencies 150 kHz-30MHz at the frequency points f was calculated for 50 batches of product and 1 reference sample according to the disclosure (1) in this case. According to the EMC test principle, if the frequency spectrum of a tested product exceeds the standard at any frequency point, the EMC of the product is unqualified; if the EMI amplitude of the frequency point corresponding to the maximum difference value of the tested product is still lower than the EMI limiting line specified by the EMC standard so as to meet the EMC standard, according to the basic principle 1, the EMI amplitudes of the rest frequency points of the product are necessarily lower than the EMI limiting line specified by the EMC standard because the difference value is smaller than the maximum difference value, so that the EMC of the product is qualified. The present case therefore only calculates the maximum value of the difference, the result of which is shown in fig. 3. Wherein the X-axis coordinates are numbers of the batch products, only the 1 st to 20 th batch products being labeled for clarity; the Y coordinate is the electromagnetic interference intensity; each point gives the calculation result in the format of (product number, maximum deviation value corresponding to frequency, maximum deviation value). FIG. 3 shows that the maximum deviation values for the batches other than batches 8 and 11 are both less than 1.9dB, and PASS was calculated according to equation (2). The maximum deviation of the batch product 8 reached 75.79dB, which was calculated as FAIL according to equation (2), and the reason for this was checked as the filter capacitor of the power supply section was disconnected; the maximum deviation of the batch product 11 reaches 19.96dB, which is calculated as FAIL according to equation (2), and the cause is abnormal operation of the oscillator circuit. The causes of EMC state failures of the batch products 8 and 11 are related to the quality of the products, so that the method can be used for quality control of the products.

Example 2

In example 2, a mass product was the same as in example 1 except that the frequency spectrum of the reference sample was replaced with an interference limiting line in the EMC test standard. When the method is operated according to the formulas (1) and (2), margin and uncertaintiy can take any values. The analysis results are shown in FIG. 4. Fig. 4 shows that the maximum values of the differences of the products other than the batches 8 and 11 fluctuate in a narrow region, and that the maximum values of the differences of the batches 8 and 11 fluctuate widely and beyond the narrow region, reflecting that the quality of both products may be problematic.

Example 3

In example 3, the evaluation method was similar to that of example 2, except that an arbitrary line segment was used instead of the spectrum of the reference sample. In the operation according to the formulas (1) and (2), margin is an arbitrary constant, and this embodiment is set to be slightly larger than the narrow region, so that the batch product with the difference value fluctuating in the narrow region is qualified by calculation according to the formula (2). The analysis also shows that the maximum of the difference between the products other than the batches 8 and 11 fluctuates in a narrow region, and that the maximum of the difference between the batches 8 and 11 fluctuates considerably beyond this narrow region, reflecting that the quality of both products may be problematic. The application of the embodiment focuses on finding batch products with abnormal work so as to realize the quality control of the products.

The above embodiments are merely illustrative of the principles and functions of the present invention, and do not limit the present invention. There may be many variations to these diagrams or the steps (or operations) described therein associated with the embodiments without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted or modified. All of these variations are considered a part of the present invention. Therefore, it will be apparent to those skilled in the art that modifications and variations can be made in the above-described embodiments without departing from the spirit of the invention. The scope of the invention is to be determined by the claims appended hereto.

Claims

1. A quality control method of batch products is characterized in that electromagnetic interference characteristics of products are taken as criteria for controlling quality factors except the electromagnetic interference characteristics of the products, and the method comprises the following steps:

giving an arbitrary line segment;

selecting an evaluated batch of products and acquiring a frequency spectrum of the products;

comparing the frequency spectrums of any line segment and batch products and observing the difference fluctuation of the two;

and if the difference value fluctuation is abnormal, checking whether quality factors except the electromagnetic interference characteristics of the product with the abnormal difference value fluctuation meet the design requirements.

2. The method of claim 1, wherein comparing the spectrum of the batch product with any of the line segments comprises:

wherein, R is the difference between the electromagnetic interference spectrum and any line segment, f is a certain frequency in the spectrum, se is the electromagnetic interference spectrum of the product to be evaluated, sr is any line segment, estatus is the product quality evaluation result, margin is the specified difference fluctuation area, any constant can be taken, uncertaintiy is the measurement uncertainty, any constant can be taken, PASS is normal, FAIL is abnormal, and UNCERTAIN is UNCERTAIN.

3. The method of claim 2, wherein R is a maximum value of a difference between an electromagnetic interference spectrum and an arbitrary line segment.

4. The method for controlling the quality of a batch product according to claim 1, wherein the checking whether the quality factors other than the electromagnetic interference characteristics of the product with abnormal difference fluctuation meet the design requirements comprises: checking whether the product works abnormally.