Tektronix TDS5000B Series, Онлайн руководство пользователя

Страница: 228 / 420

228
Note
The terms vertical acquisition window and horizontal acquisition window refer to the vertical and
horizontal range of the segment of the input signal that the acquisition system acquires. The terms
do not refer to any display windows on screen.
Probes and Signal Connection
Select the probe or cable that brings the signal into the instrument. Choose the probe or cable that
best fits your acquisition task, whether it is connecting an active probe to test a digital circuit, or
connecting to a test fixture through BNC cables to characterize a device. The connection to the
instrument depends on your application.
Up to four acquisition channels are available. You can display each channel as a waveform and/or
use the channel data to create other waveforms, such as math and reference waveforms.
Tektronix provides a variety of probes and cables for this product. You can also check your
Tektronix catalog for connection accessories to support your probing requirements. For more
information about a particular probe, read the documentation that came with that probe.
Coupling
All instruments and probes specify a maximum signal level. Do not exceed the limit, even
momentarily, as the input channel or probe may be damaged. Use external attenuators if necessary
to prevent exceeding the limits.
Coupling determines whether an input signal is directly connected to the input channel (DC
coupling), connected through a DC blocking capacitor (AC coupling), or not connected at all
(GND coupling).
The input resistance of each input channel is 1 M
Ω
or 50
Ω
. To properly terminate signals when
using coaxial cables, or to support active probes designed for a 50
Ω
environment, a 50
Ω
termination resistance can be selected by pushing the front-panel termination button for a
particular channel.
All probes expect a specific coupling and input termination. Both coupling and input termination
are displayed on the screen. If the instrument determines the coupling and termination required by
the probe, either implicitly because of the TEKPROBE interface or through performing a probe
calibration, the instrument sets the required coupling and input termination.
Consider the following when you use 50
Ω
termination with any channel:
ƒ
The instrument does not accurately display frequencies under 200 kHz if AC coupling is
selected.
ƒ
The instrument reduces the maximum volts per division setting for the channel to 1 V from
10 V (10 V from 100 V with a 10X probe attached), since input amplitudes appropriate for the
higher settings would overload the 50
Ω
input.
ƒ
The instrument switches to 50
Ω
termination and DC coupling if you connect an active probe.
Active probes also reduce the maximum volts per division.
Scaling and Positioning
The scaling and positioning controls determine the portion of the input signal received by the
acquisition system. Set vertical scaling, positioning, and DC offsets to display the features of
interest on your waveform and to avoid clipping.