Dataman 520 Series - Manual (Page 15)

DATAMAN oscilloscope
User’s Guide
the input signal The trigger event is generated with respect to a change of the selector
(PTSS, STSS) output signal from 0 (FALSE) to 1 (TRUE). A constant level of the
signal cannot start the measurement. In the case that only one of the signals is selected
the trigger event is generated corresponding to the polarity, which is symbolically
presented by the 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. A 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 the selector
input signal should have before a 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, consequently the 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 the 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. 2.1.2.2. – 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 the trailing edge (1 to 0). If the pulse is inverse (1 to
0 to 1), the trigger event should be set to the leading edge (1 to 0). The outputs of the
digital pulse filters are connected to event counters (EC). It counts the unfiltered
pulses. If the MS switch is set to the primary level, the output of the 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 the secondary level, the output of the 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.
- 15 -