EM TEST
EFT 500 Series
Manual for Operation
V 2.00
15 / 21
For conducting the test the following points shall be taken under consideration:
1. It is not allowed to touch the EUT or the cables under test during a running test. The test results will be
influenced and are no more reproducible.
2. If the operator in contrary touches directly the EUT or the connected lines increased radiation from the test
set-up is generated. The operator itself will radiate and/or will cause ground currents into the whole
environment.
3. As larger the dimensions of an EUT are, as higher the radiation of high frequency energy will be.
4. Especially the capacitive coupling clamp with its length of 1m radiates.
5. Auxiliary equipment as well as computer can be influenced directly due to the radiation.
Remarks:
Even the use of fiber-optic links for the communication between a computer and EFT does not help in case of
direct radiation. The computer and its lines will be directly influenced and the data transmission will be disturbed.
6. The influence of direct radiation can be reduced by increasing the distance between a computer and the test
set-up. In any case a minimum distance of 3m shall be available.
It is not only the length of the cable but also the physical distance between computer and test set-up which is
important to take care to.
7. It is shall be strictly avoided to put the computer directly onto the ground reference plane of the test set-up.
The computer then is part of the test set-up and will also be tested. Mostly all computers are not immune to
this test and will be disturbed.
What to say about the computer:
1. Do not use oldest equipment available in your company. Actual computer show better behavior to what EMC
concerns.
2.
Do not use notebooks for this application. Laptops are fully manufactured within a plastic housing and therefore
are very sensitive to all kind of interference.
4. It would be better to use tower- or mini-tower equipment. They are at least partially screened. The interface
connectors are mounted on metallic surfaces so that the screen of the communication lines can be connected
to the chassis.
5. The screens of the RS 232 and IEEE cables must be connected to the chassis of the instruments at both
sides, at the computer and at the EFT generator.
6.
The communication cables, RS 232 and IEEE, shall be screened. Do not use standard cables, consumer products
with plastic connectors.
These cable types are using mostly very bad designed cable screens. The contact to the housing of the
connector is mostly realized with a small cable, which is very bad under the aspect of rf screening.
Please take care that the screen is connected very good to the metallic housing of the connector and that the
connector is screwed to the housing of the generator.
This mostly is the problem when using the RS 232 interface. Especially those cables are badly designed. For IEEE
cables very good products are available (e.g. HP).
7. The weakest parts within the computer system are the peripherals, as keyboard and mouse. Both products
are not designed to operate under these severe conditions.
It is very easy to make the design better. The operator would be able to do it for himself.
What is the problem ?
The screen of the cables between a computer and the keyboard (mouse) are soldered directly to the printed
circuit board.
The screen shall not be soldered to the print, but to another „ground reference plane“.
e.g. put into the keyboard, directly under the keyboard print a broad copper foil area. Connect the screen of the
cable to this copper foil, without any connection to the print. You will see a dramatic change to better results.
