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Vertical Control
TDS 620A, 640A & 644A User Manual
3Ć137
Vertical Readout
Figure 3Ć74:ăVertical Readouts and Channel Menu
Coupling
To choose the type of coupling for attaching the input signal to the vertical
attenuator for the selected channel and to set its input impedance:
Press VERTICAL MENU ➞ Coupling (main) ➞ DC, AC, GND,orW(side).
H DC coupling shows both the AC and DC components of an input signal.
H AC coupling shows only the alternating components of an input signal.
H Ground (GND) coupling disconnects the input signal from the acquisiĆ
tion.
H Input impedance lets you select either 1ĂMW or 50 WĂ impedance.
NOTE
If you select 50 W impedance with AC coupling, the digitizing
oscilloscope will not accurately display frequencies under 200 kHz.
Also, when you connect an active probe to the oscilloscope (such
as the P6205), the input impedance of the oscilloscope automatiĆ
cally becomes 50 W. If you then connect a passive probe (like the
P6139A), you need to set the input impedance back to 1ĂMW.