LeCroy SDA, Operator'S Manual

Page: 77 / 397

SDA Operator’s Manual
SDA-OM-E Rev H
77
Trigger Source
The Trigger On source may be one of the following:
•
The acquisition channel signal (CH 1, CH 2, CH 3 or CH 4) conditioned for the overall voltage
gain, coupling, and bandwidth.
•
The line voltage that powers the oscilloscope (LINE). This can be used to provide a stable
display of signals synchronous with the power line. Coupling and level are not relevant for
this selection.
•
The signal applied to the EXT BNC connector (EXT). This can be used to trigger the
oscilloscope within a range of ±400 mV on EXT, ±4 V with EXT/10 as the trigger source, or
±40 mV with EXT*10 as the trigger source.
•
A logic pattern.
Level
Level defines the source voltage at which the trigger circuit will generate an event (a change in
the input signal that satisfies the trigger conditions). The selected trigger level is associated with
the chosen trigger source. Note that the trigger level is specified in volts and normally remains
unchanged when the vertical gain or offset is modified.
The Amplitude and Range of the trigger level are limited as follows:
•
±4.1 screen divisions with a channel as the trigger source
•
±400 mV with EXT as the trigger source
•
±4 V with EXT/10 as the trigger source
•
±40 mV with EXT*10 as the trigger source
•
none with LINE as the trigger source (zero crossing is used)
Note: Once specified, Trigger Level and Coupling are the only parameters that pass unchanged from trigger mode to
trigger mode for each trigger source.
Holdoff by Time or Events
Holdoff is an additional condition of Edge trigger. It can be expressed either as a period of time or
an event count. Holdoff disables the trigger circuit for a given period of time or number of events
after the last trigger occurred. Events are the number of occasions on which the trigger condition
is met. The trigger will again occur when the holdoff has elapsed and the trigger's other
conditions are met.
Use holdoff to obtain a stable trigger for repetitive, composite waveforms. For example, if the
number or duration of sub-signals is known you can disable them by choosing an appropriate
holdoff value. Qualified triggers operate using conditions similar to holdoff.