Dataman 520 Series - Manual (Page 24)

DATAMAN oscilloscope
User’s Guide
signal cannot start the measurement. In case that only one of the signals is selected,
trigger event is generated corresponding to the polarity, which is symbolically
presented by direction of change of the signal. (0 to 1 means no inversion). When
there are several inputs selected, the selector makes a logical addition (OR) of all of
the selected inputs. Before adding the signals together, ones are adjusted with respect
to the polarity settings. Trigger event is generated only when the change of result of
the logical addition occurred from 0 to 1 (FALSE to TRUE). Logical values of the
signals in the input of logical adder (OR) from which the trigger event is generated are
created on the basis of following rules: value 0 (FALSE) is the value that selector
input signal should have before valid trigger event. 1 (TRUE) is the value that this
signal will have after the valid trigger event. For example, if triggering from Channel
A is set to the trailing edge, then the output voltage of the channel is higher than the
threshold voltage, consequent value on the adder input will be 0 (FALSE). Inverse
situation will be taken as 1 (TRUE). Note that when using logical addition, all values
must be 0 (FALSE) in order for result to be 0 (FALSE). It is relatively easy to find out
which are the valid trigger events. Figure 2.1.2.2 shows several valid and invalid
trigger events (all inputs are enabled).
A B E
valid
invalid
invalid
valid
valid
selected
trigger event
Fig. 2.3.2.2. – Examples of trigger events (all inputs are enabled)
The digital pulse filters (DF) are implemented in both primary and secondary trigger
levels. If activated, they filter out pulses shorter then the value 4*N*Ts, where Ts is
the actual real time sampling period and N is the value set by the user (1 <= N <=
32767). If we want to use this option it is necessary to set the valid trigger event to the
end of the pulse. For example, if the pulse we want to filter off is positive (0 to 1 to 0)
the trigger event should be set to trailing edge (1 to 0). If the pulse is inverse (1 to 0 to
1), the trigger event should be set to leading edge (1 to 0). The outputs of digital pulse
filters are connected to event counters (EC). It counts the unfiltered pulses. If the MS
switch is set to primary level, the output of primary event counter will change from 0
(FALSE) to 1 (TRUE) to indicate the valid trigger event after reaching the terminal
count, which is user selectable in the range of 1 to 32767. If the MS switch is set to
secondary level, the output of primary event counter activates the secondary trigger
level. The input selector, digital filter and event counter can be set for secondary level
independently to define the valid trigger event.
The trigger circuits of the series DATAMAN 770 DSOs are equipped with Hold Off
timer (TDL). It blocks the triggering event for time period T=4*H*Ts from the start
of data acquisition, where Ts is the actual real time sampling period and H is the user
- 24 -