Voltage Probes For Isolated Amplifiers (High Accuracy) - HBM Genesis GEN5i User Manual

GEN5i
D.2.3

Voltage probes for isolated amplifiers (high accuracy)

Voltage probes for isolated amplifiers divide down an isolated input signal by a
specific factor. They are designed in an "isolated way", 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.10: Typical example of a high accuracy voltage probe for isolated
amplifiers – done as external divider
Isolated voltage probes are usually just passive in-line resistors in front of the
positive input of an isolated amplifier. Unfortunately this decreases the accuracy
of the overall system.
However, isolated voltage probes can also be designed to overcome these
drawbacks.
To achieve this, they are not only in-line resistors, but they form a complete,
high accuracy voltage divider in front (and in parallel) of the amplifier input. So
the accuracy is determined mainly by the probe itself and maintained at high
level.
There is still a capacitive component in this divider, so the amplifier and the
probe need to match each other. Only a specific combination of probe and
amplifier then can maintain high overall accuracy.
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.
518 I2679-4.0 en