Voltage Probes For Isolated Amplifiers - HBM Genesis GEN5i User Manual

GEN5i
D.2.2

Voltage probes for ISOLATED amplifiers

Voltage probes for isolated digitizers divide down an isolated input signal by a
specific factor. They are designed in an "isolated way" (like plastic BNC´s to
prevent users touching the connection), so they can be used in front of an
isolated unbalanced amplifier. So they are also called "isolated voltage probes",
though they do not add isolation; this comes from the amplifier.
Figure D.9: Typical example of an isolated voltage probe
Voltage probes for isolated amplifiers are also – in theory – just passive in-line
resistors in front of the positive input of an isolated unbalanced amplifier.
Together with the input resistor of the amplifier they form a voltage divider, so
that the voltage in front of the amplifier itself gets divided down. As there is also
a capacitive component in this divider, the input capacitance of the amplifier
and the so called "compensation range" of the probe need to match, otherwise
signal distortion might occur.
As the dividing down, however, only applies to the positive side of the amplifier
input, the input range gets increased, while the isolation voltage remains the
same as without probe.
These probes can only be used in front of isolated unbalanced amplifiers.
Isolated voltage probes typically decrease the overall accuracy of the system
(caused by the inaccuracy of the input divider ratio formed by the external probe
resistance and the internal amplifier resistance).
516 I2679-4.0 en