Tektronix 2440, User Manual

Page: 14 / 531

Specification— 2440 Service
delay may be set from 1 to 65,536, with a resolution of
one event. The DELTA DELAY feature produces two
independently settable delayed B Traces in DELAY
by TIME.
TRIGGER SYSTEM
The trigger system of the scope provides many features
for selecting and processing a signal used in triggering the
acquisition system. The conventional features of SOURCE
selection, Trigger LEVEL control, Trigger SLOPE, Trigger
MODE, and CPLG (coupling) include enhancements not
normally found in a conventional oscilloscope.
The choices of VERT, C H I or CH2, EXT1 or EXT2,
LINE, and A 'B or W ORD (16-bit data word recognition) are
available as SOURCE selections for triggering A Horizontal
Mode acquisitions. These sources for trigger signals
provide a wide range of applications involving specialized
triggering requirements. Except for A*B (A AND B) and
LINE (power-source frequency), the same Trigger
SOURCE selections are available for triggering B acquisi­
tions. The selected trigger signal is conditioned by the
choice of input CPLG (coupling). These coupling selections
are AC, DC, HF REF, LF REJ, and NOISE REJ. LEVEL
control provides a settable amplitude (with C RT readout)
at which triggering will occur, and SLOPE control deter­
mines on which slope of the triggering signal (plus or
minus) the acquisition is triggered.
Trigger MODE choices are AUTO LEVEL, AUTO,
NORM, and SINGLE SEQ (single sequence), for the A and
A INTENSIFIED Modes, and Triggerable After Delay and
Runs After Delay, for the B Mode. AUTO LEVEL provides
for automatic leveling on the applied trigger signal. AUTO
MODE produces an auto trigger in the event a trigger
signal is either not received or not within the limits needed
to produce a triggering event. When triggering conditions
are met, a normal triggered display results. At SEC/DIV
settings of 100 ms per division and longer, the AUTO
MODE switches to ROLL. In ROLL MODE, the display is
continually updated and trigger signals are disregarded.
NORM (normal) trigger MODE requires that all
triggering requirements are met before an acquisition will
take place. SINGLE SEQ (single sequence) MODE is a
variation of the conventional single-shot displays found on
many previous oscilloscopes. In SINGLE SEQ, a single
complete acquisition is done on all called-up VERTICAL
MODES. Since an acquisition depends on the acquisition
mode in effect, many of the scope operating features are
altered in SINGLE SEQ. A complete description of this
mode is discussed in ‘ Controls, Connectors, and
Indicators” in Section 5 of the Operators manual.
The user has a choice of trigger points within the
acquired waveform record by selecting the amount of pre­
trigger data displayed. The trigger location in the record is
selectable from a choice of five pretrigger lengths
beginning at one-eighth of the record length and increasing
to seven-eighths of the record length. A record trigger
position is independently selectable for both A and B
acquisitions. Additional trigger positions in the record are
selectable via the GPIB interface commands.
CURSOR MEASUREMENTS
Time and Voltage cursors are provided for making
parametric measurements on the displayed waveforms.
Time may be measured either between the cursor
positions (DELTA TIM E) or between a selected cursor and
the trigger point of an acquired waveform (ABSOLUTE).
Time cursor readouts are scaled in seconds, degrees, or
percentage values. The 1/TIM E cursors may be scaled in
hertz (Hz), degrees, or percentage.
Voltage cursor measurements on a waveform display
can be selected to read either the voltage difference
between the cursor positions or the absolute voltage posi­
tion of a selected cursor with respect to ground. The volts
measurement readouts may be scaled in units of volts,
decibels (dB), or percent. The Voltage cursors and Time
cursors may also be coupled to track together (V @ T and
SLOPE) and assigned to a particular waveform for ease in
making peak-to-peak and slope waveform measurements.
The units for V @ T may be volts, percent, or dB; SLOPE
may have units of slope (VOLTS/SEC), percent
(VOLTS/VOLT), or dB.
WAVEFORM ACQUISITION
Waveforms may be acquired in NORMAL, ENVELOPE,
or AVG (Average) acquisition modes; the mode chosen
depends on the measurement requirements. NORMAL
mode continuously acquires and displays successive
acquisitions producing a “live” waveform display similar to
that seen with an analog oscilloscope. AVG (averaging)
mode averages successive acquisitions of a waveform
resulting in an improved signal-to-noise ratio of the
displayed waveform. Low-amplitude signals masked by
noise become easily visible for making measurements and
analysis by averaging from 2 to 256 acquisitions for
removing uncorrelated noise. ENVELOPE mode saves the
1-2