Operating Basics
Many handheld o
scilloscope products have the architecture s hown below, which
shares a common reference for the oscilloscope channels. (See Figure 8.) With
this architecture, all input signals must have the same voltage reference when you
take any multi-channel measurements.
Figure
8: Common-reference input architecture
Most b
ench-top oscilloscopes share the architecture shown above, but without
the ins ulated case. Without differential preamplifiers or external signal isolators,
bench-top oscilloscopes are not suitable for taking floating measurements.
For oscilloscopes with isolated inputs, references are not connected together
inside the instrument. Therefore, each reference of the used inputs must be
connected to a reference voltage. Independently floating isolated inputs are still
coupled by parasitic capacitance. This can occur between the input references and
the environment, and between the input references mutually. For this reason, you
sho
uld connect the references to a system ground or another stable voltage. If the
reference of an input is connected to a high speed and/or high voltage signal, you
should be aware of parasitic capacitance. (See Figure 9 on page 21.)
NOTE. The input channels are electrically isolated from the USB ports and from
the power adapter input.
THS3000 Series Oscilloscopes User Manual 19
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