How can you really take advantage of EMSCAN_Century Wisdom (Suzhou) Testing Technology Co., Ltd

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How can you really take advantage of EMSCAN

Release time:

2013-01-22 00:00

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As we all know, during EMI test or even EMS (continuous wave) test, engineers will always encounter the situation that the test cannot pass, and how to locate the "hot spot" of EMI or the "sensitive point" of EMS is the prerequisite for solving the problem.

A typical EMI "hot spot" location system includes:

Ø Near field probe

Ø Preamplifier

Ø Spectrum Analyzer

Among them, the near-field probe plays the role of detecting the signal, and the spectrum analyzer plays the role of identifying the signal. If the signal is small enough, a preamplifier is required.

Judging from the current situation, the near-field test cannot simulate the far-field test results, because there is an essential difference between the two tests. The former is a relative measurement, which uses the magnetic or electric field components induced by the near-field probe. , the typical wave impedance distribution in the near-field area presents the following characteristics:

Therefore, in the near-field area, both the electric field impedance and the magnetic field impedance are in an unstable state. The impedance presented is completely different depending on the test distance, so the distance has a great influence on the near-field measurement.

At the same time, the physical shape of a normal magnetic field probe is a typical circular characteristic, and only the direction through which the magnetic field lines pass can be tested. The test characteristics of a typical near-field probe are as follows:

Therefore, different angles have a great influence on the test results.

For the uncertainty of manual testing, including distance, angle, and direction, the world's leading near-field testing tool is currently the EMSCAN product designed and manufactured by Canada's EMSCAN Company, which typically has the following characteristics:

Ø Fixed near-field probe

Ø 90-degree probe distribution between two rows

Ø Advanced analysis software

This design concept can avoid the test error caused by the uncertainty of the position of the probe to the greatest extent, and can better complete the positioning of EMI "hot spots".

But no matter how advanced the tool is, as long as its principle is based on the near-field probe, the results obtained can only be near-field data under any circumstances, and cannot truly simulate the far-field test results.

In response to this situation, EMSCAN has designed a special module function of "far-field filtering". The design principle is based on the fact that the frequency points exceeding the standard in the far-field test must exist in the near-field. The test process is as follows:

Ø Test near-field results

Ø Test the far-field results when the EUT is turned off

Ø Test the far-field results when the EUT is turned on

Through the automatic comparison function of the software, it is possible to identify which frequency points exceeding the standard in the far field are based on the near field, and the insensitivity of the near field test itself to the environment determines that these frequency points basically belong to the EUT itself, thus completing EMI pre-compliance testing.

However, this test method needs to meet the following conditions:

Ø A site large enough to simulate an open field

Ø "stabilization" of background noise

It is not easy to achieve both of these at the same time. First of all, the ordinary office environment cannot meet the conditions of use at all, and it is not easy to meet the conditions of an open field in a large enough site. Electricity is used for basic construction, and at the same time, auxiliary equipment and noise in the environment are unlikely to be in a stable state, including frequency and amplitude.

Therefore, the typical EMSCAN suggested matching environment is a darkroom. When users already have a darkroom, they can locate EMI "hot spots" or EMS "sensitive points" more quickly, so as to solve problems relatively easily.

Even if these hotspots or sensitive points are found, it is more important to solve these hotspots or sensitive points, and the data of the near-field test has little reference value for the results of the far-field, because:

Ø The system often consists of multiple boards

Ø If the external chassis of the system is made of metal, it is easy to change the distribution of the electromagnetic field

Ø The cable of the system will amplify the influence of the near field

So the suggested process is:

Ø Standard test of far field

Ø Diagnosis, positioning and debugging in the near field

Ø The re-testing of the far field confirms

Therefore, it is possible to make good use of EMSCAN only under the conditions of a dark room, otherwise the help for quickly passing the EMI test is very limited. However, it is very difficult to solve the problem of EMI radiation through EMSCAN itself and the supporting "background noise filter" in a common environment.

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