TDS 684A, TDS 744A, & TDS 784A User Manual E–1
Appendix E: Probe SelectionThe TDS Oscilloscope can use a variety of Tektronix probes for taking different
kinds of measurements. To help you decide what type of probe you need, this
section introduces the five major types of probes: passive, active, current,
optical, and time-to-voltage probes. See Appendix A: Options and Accessories
for a list of the optional probes available; see your Tektronix Products Catalog
for more information about a given probe.
Tektronix ships the P6139A passive probe with the TDS 744A Oscilloscope as a
standard accessory. The TDS 684A and TDS 784A Oscilloscopes ship without
standard probes but Tektronix recommends you order the P6245 active probe to
take advantage of the 1 GHz bandwidth of these two oscilloscopes.
NOTE. The TDS 744A comes with four P6139A passive probes. The TDS 684A
and TDS 784A Oscilloscopes come without probes, but for general purpose
measurements and to take advantage of the wide bandwidth of these two
oscilloscopes, the P6245 Active Probe is recommended. This manual lists the
P6245 optional-accessory probe in Appendix A: Options and Accessories.
Passive Voltage Probes
Passive voltage probes measure voltage. They employ passive circuit compo-
nents such as resistors, capacitors, and inductors. There are three common
classes of passive voltage probes:
General purpose (high input resistance)
Low impedance (ZO)
High voltage
High input resistance probes are considered “typical” oscilloscope probes. The
high input resistance of passive probes (typically 10 MW)provides negligible
DC loading and makes them a good choice for accurate DC amplitude measure-
ments.
However, their 8 pF to 12 pF (over 60 pF for 1X) capacitive loading can distort
timing and phase measurements. Use high input resistance passive probes for
measurements involving:
Device characterization (above 15 V, thermal drift applications)