Level Triggering; Level Triggering Examples - Agilent Technologies 3458A User Manual

Level Triggering

Level Triggering

Examples
132 Chapter 5 Digitizing
When digitizing, it is important to begin sampling at some defined point on
the input signal such as when the signal crosses zero volts or when it reaches
the midpoint of its positive or negative peak amplitude. Level triggering
allows you to specify when (with respect to voltage and slope) to begin
sampling. For example, Figure 26 shows sampling beginning as the input
signal crosses 0V with a positive slope.
Figure 26. Level triggering at zero crossing, positive slope
For DCV and direct sampling, level triggering can be used as the trigger event
(TRIG LEVEL command) or the sample event (NRDGS n, LEVEL
command). For sub-sampling, level triggering can be used as the sync source
event only (the sync source event is discussed later in this chapter under
"Sub-Sampling"). The program examples in this section use the DCV method
of digitizing and the 10V range. Refer to "DCV Digitizing",
"Direct-Sampling" and "Sub-Sampling" later in this chapter, for complete
programs showing specific information on how to use level triggering with
each digitizing method.
The LEVEL command specifies the level triggering voltage as a percentage
of the measurement range. {The ranges are shown later in this chapter under
the discussions for each digitizing method,) The LEVEL command also
specifies the coupling (AC or DC) to the level detection circuitry.
Note
The coupling of the input signal can affect the level trigger coupling. That
is, if you select AC coupling for the input signal (e.g., DSAC or SSAC) the
level trigger signal will also be AC coupled regardless of the specified level
trigger coupling. When the input signal is DC coupled (e.g., DCV, DSDC,
SSDC) however, you can control the coupling of the level trigger signal
with the LEVEL command. The level trigger coupling does not affect the
input signal coupling.
The SLOPE command specifies the slope of the signal to use. The power-on
or default values for these commands specify a level percentage of 0% of the
present range (trigger when the signal crosses zero volts}, positive slope, and
AC-coupling to the level detection circuitry. So, in the power-on state, you