Once test occurred some failure, the lab quickly informs the customer. But where not all is is actual failure, so we need check whether the failure is actual or virtual.

1.       Judgment requirement

The lab mistake the level 1 requirement to level 2, this is quick to check. Now, we often use the threshold to judgment level 1 test result, in general, level 1 is different from level 2 with 6dB, so if the threshold is less than 5dB,it is safe, but if it is more than 5dB,less than 7dB, we should carefully check, it is recommended adding to test level 1.

2.       Calibration level

In order to save the test time, the lab always uses the threshold. But if the threshold is too much, the threshold will be not correct. In principle, for example 15MHz, 80mA threshold value was calculate by 200mA calibration value, it should be near, but in fact, because the power is not linear, the software can not correctly calculate, it relatively more high the 80mA value.

3.       Threshold

In particular, PM and AM mode, it is better to reduce the inject level, more level, more the field unstable, had better 1dB.

Experience, the test lab will speed up the test, they often will use 6dB step to inject the current or the voltage or the power, so this will add the risk to fail to test.

4.       DUT orientation

In automotive EMC test, in general, the antenna is far away from the DUT and Harness 1m, so regulate the DUT orientation will obviously change the radiated level. Reducing 2dB is possible.

Experience, if not specified, it is possible the heat dissipation hole will not face with the antenna, and calculate the waveform length of the emission.

5.  Harness

    If the customer is not specified, the differential pair must be twisted; battery line and ground line had better twist together, and arrange the twisted pair line outside the harness.

SGM required the AM/FM BNC bundle together to the harness. Had better the wonderful shielding BNC, will reduce to directly interfere the signal, and change the field of injection loop. And due to the dummy will connect with the ground, it also change the DUT ground connection.

5.       DUT is remotely grounded or locally grounded

According to the vehicle mounting, if DUT connect with plastic, not fixed on metal house, this is locally grounded. 

As for BCI/RI, from 10M-20MHz, DBCI or CBCI, this affect very much. Above 200MHz, locally grounded will improve the DUT immunity.

As for CE, the junction of locally grounded is very important, must choice relative clean ground to connect with the metal ground plane.

As for RE, locally grounded is better than remotely, this will change the field distribution of metal housing in emission frequency.

As for CI, should confirm the audio analyzer, oscilloscope and generator, these ground and power whether will affect the test result. Must ensure these grounds didn’t make the loop.

6.       Accessory

a.       CAN transceiver/Lin transceiver

There is much noise from 1MHz 30MHz, and will evaluate the ambient.

When test RI, sometime will directly interfere the transceiver.

Whether the battery is full?

b.       Dummy

As for BCI and RI, the good ground connection is needed. The short BNC on the dummy had better good shield.

c.       BNC

As for RE, the AM/FM BNC had better layout in the wedge, otherwise, the potential source will bring the enveloping noise from 30MHz to 200MHz.

d.       Battery

Low battery voltage will affect the test result on RI/BCI test.