NARDA PMM ER9000, User Manual

Page: 49 / 106

Applications 4-3
4.1.2.2 Current Probe
Current Probes may be Clamp-on Probes or Fixed-ring Probes.
Current Probes are used to measure differential or common mode RFI
currents. In some cases it may be important to make a distinction between
the two kinds of current flowing in a system.
RFI current measurements with Current Probes may be required, for
example, when measuring EMI from shielded lines or from complex wiring
systems, when finding interference sources among other sources in a
system, when performing compliance to some Standards, etc.
4.1.2.3 Voltage Probe
Voltage Probes include Active Probes and Passive Probes.
Active Probe has a very high input impedance Zin > 100 K
Ω
// < 10 pF.
Passive Probe has a standard impedance Zin = 1,5 K
Ω
// < 10 pF.
Voltage Probe is used for measuring the unsymmetrical RFI voltage when it
is not possible to carry out measurement by interconnecting an Artificial V-
type Network. Such situation may occur, for example, when measuring on
lines on which only small loads are permissible (control and signal lines),
when measuring on a EUT (Equipment Under Test) which would not
operate correctly using V-type LISN or a DUT (Device Under Test)
requiring very high power supply current for which no V-type LISN is
available.
For diagnostic or design purposes on high impedance circuits, Voltage
Probe may be used to determine, for example, noisy components or
conductors that cause interference on CMOS PC boards.
Some Regulations give statements when Voltage Probe are to be used and
specify relevant setup and RFI voltage limits.
4.1.3 Test Setup
A general test layout for a simple table top EUT is according to figure 4-2.
Some product/family product standards may prescribe different
requirements.
The EUT shall be placed 0,4m from a ground reference plane of at least
2m x 2m in size, either horizontal or vertical. If the measurements are made
in a shielded room, the EUT shall be placed 0,4m from either one of the
walls of the room or the conducting floor.
All other earthed conducting surfaces shall be at least 0,8m apart from the
EUT.
Floor-standing EUTs are subject to the same provisions as above with the
exception that they shall be placed on a floor, the points of contact being
consistent with normal use. In this case the ground reference plane end
shall extend at least 50 cm beyond the boundaries of the EUT and have
minimum dimensions of 2m by 2m. The floor standing EUT shall be
isolated by the ground reference floor and kept at a maximum distance of
0,15m.
The power cable should be 1m long; longer cable should be centrally
bundled for at least 0,4m.
EUTs without a PE (Protective Earth) conductor and handheld DUTs shall
be measured in conjunction with an auxiliary screen or an “Artificial Hand”,
as duly specified in the relevant standards.