Appendix D: Probe Selection
TDS 500D, TDS 600B, & TDS 700D User Manual
D–3
Figure D–1: Typical High Voltage Probes
Active Voltage Probes
Active voltage probes, sometimes called “FET” probes, use active circuit
elements such as transistors. There are three classes of active probes:
High speed active
Differential active
Fixtured active
Active voltage measuring probes use active circuit elements in the probe design
to process signals from the circuit under test. All active probes require a source
of power for their operation. Power is obtained either from an external power
supply or from the oscilloscope itself.
NOTE. When you connect an active probe to the oscilloscope (such as the
P6245), the input impedance of the oscilloscope automatically becomes 50 . If
you then connect a passive probe, you need to set the input impedance back to
1M. The procedure To Change Vertical Scale and Position on page 3–16
explains how to change the input impedance. Also, please read Input Impedance
Considerations on page 3–8 for more information.
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