- 21 -
LANGER
EMV-Technik
DE-01728 Bannewitz
[email protected]
www.langer-emv.com
ESA1
This set-up has a disadvantage: the voltage differences remaining from the areas of the basic unit,
plug-and-socket connector and GND of the interface module are measured as well. Wherever
functionally possible, you should initially operate the interface module separately without the basic
unit (
Figure 31
). The module's performance characteristics, e.g. without data being sent by the
basic unit, will of course differ from those under normal operating conditions. If the clock line works
and the processor is in operation, however, relative measurements of the currents and fields
generated by the processor, for example, are possible. You can easily evaluate modifications to
the GND and supply systems.
Figure 31
Set-up without the basic unit
4.1.5 External data lines
1) Measuring the RF current on data lines
To measure the RF current on data lines, simulate the capacitance of the line connected under
normal operating conditions and lead the RF current through the RF current transformer (
Figure
32). The RF current circuit is closed through the capacitance of other lines relative to the ground
plate or through capacitive or conductive coupling between the unit under test and ground plate
(e.g. with battery-operated devices). This procedure is particularly suitable for dimensioning data
line filters. If the unit under test drives a remote LCD display via a ribbon cable, for example,
disconnect the lines to the display on the unit under test side and only connect one line to one of
the COM outputs of the HFW 21 via an equivalent capacitance and optimize this line first. Apply
the filter circuit you have found to other signal lines later on.
Figure 32
