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Rohde & Schwarz Probes and accessories for Rohde & Schwarz oscilloscopes 5
Expanded functions and probe accessories
In addition to the performance parameters, the supple-
mental functions for simplifying daily tasks must be con-
sidered. Examples include an integrated digital voltmeter
or a micro button. The functionality of the micro button
can be configured to allow direct control of the oscillo-
scope from the probe.
The diverse accessories offer flexibility during test point
contacting, make the operator's day-to-day work easier
and help prevent measurement errors. Available accesso-
ries include rigid and spring-loaded tips, browsers, adapt-
ers and extension leads. Rohde & Schwarz offers a compre-
hensive set of accessories for every probe.
To accurately measure steep, large-amplitude slopes, a
sufficiently wide dynamic range must be available at high
frequencies. When measuring the residual ripple of DC
switching power supplies, very small signals with a large
DC component must also be measured. To make the full
A/D converter resolution available, modern probes have
the option to feed in a DC offset.
In the case of high voltage probes, operator safety is a key
consideration. High voltage probes therefore have special
insulation, protection against accidental contact and other
protective mechanisms. These probes are characterized by
the maximum voltage to ground and by the measurement
category. The measurement category defines the measure-
ment environments in which the operator is still protected.
A probe may only be used in the measurement categories
for which it is defined.
Load on the device under test
A measurement system must not excessively load the
circuit under test, both to prevent degraded signals and
to ensure that the functioning of the DUT is not impaired.
The key is to use probes with a high input impedance and
a low input capacitance. The resulting input impedance
is highly dependent on the frequency and is typically less
than 500Ω at the probe's cutoff frequency.
Passive probes typically have an input impedance of
10MΩ and an input capacitance of >10pF. Active probes
typically have an input capacitance of <1pF at an input
impedance of 1MΩ and are especially suited for measure-
ments on circuits with high-speed signals >100MHz. For
the measurement, it is important to select the right probe
accessories for contacting with the DUT. Long pins and
leads increase the capacitance and inductance, lower the
maximum measurement bandwidth and lead to excessive
overshoot and ringing artifacts at the pulse slopes.
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