15.2.2
Passive, single
-
ended isolated voltage probes
Passive, single
-
ended isolated voltage probes divide an isolated input signal
by a specific factor. They are designed in an “isolated way” (like plastic BNCs
to prevent users from touching the connection) so they can be used in series
with an isolated unbalanced amplifier. They are called “isolated voltage probes”,
although the amplifier and not the probe adds the isolation.
10 * Udiff
Uiso
Uiso
Udiff
(+)
(-)
(-)
GND
GND
Single-ended isolated or
unbalanced differential amplifier
9M
900K
Isolation
Barrier
100K
(+)
(+)
(-)
Uiso
Non-isolated
system
Figure 15.8:
Typical example of an isolated voltage probe
Theoretically, voltage probes for isolated amplifiers are simply passive in
-
line
resistors in series with the positive input of an isolated unbalanced amplifier as
well.
Together with the input resistor of the amplifier, they form a voltage divider so
that the voltage in front of the amplifier itself is divided. 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.
However, as the division only applies to the positive side of the amplifier input,
the input range is increased while the isolation voltage remains the same as
without a probe.
These probes can only be used in series with 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).
GEN3t
390
I3995-3.1 en HBM: public
