Fluke PM3370B user manual Trigger Main TB

5 - 84 FUNCTION REFERENCE

TRIGGER MAIN TB

Description:

This section deals only with ‘edge’ triggering of the MAIN TB. For TV triggering, Logic triggering or DEL’D TB triggering, refer to the appropriate sections.

In the analog mode triggering determines the start point of the MAIN TB sweep. The sweep starts at the moment the signal crosses the trigger level in positive or negative direction. The slope is selectable ( ), as is shown in the figure below.

In the digital mode, the trigger system determines which part of the trace is acquired and placed in memory. As in every other Digital Storage Oscilloscope, signal acquisition through the ADC system is a continuous process, until it is stopped by the trigger signal. If nothing else would be done, the signal placed in memory would be the signal prior to the trigger moment and the trigger moment would be displayed at the end of the screen. For most oscilloscope users this would be confusing, since most users were taught that the trigger point determines the beginning of a sweep (as is the case for an analog scope).

Therefore, in actuality, a delay time equivalent to the time of one sweep length is added, so that it appears as if the trigger moment is displayed at the beginning of the screen.

The TRIGGER POSITION control allows you to change the time delay between the trigger point and the digital acquisition. If set to zero, the acquisition is stopped after a time equivalent to one sweep length has been added so that the trigger point appears at the beginning of the trace.

Any of the inputs can be used as the trigger source. The source is selected with the keys ‘TRIG1, TRIG.. or EXT TRIG’ in the respective control sections. The same keys are used to toggle between the positive ( ) and negative ( ) slope. In the digital mode, dual slope ( ) is available. The oscilloscope must be set to ’REAL TIME ONLY’ = yes in the TB MODE menu. Dual slope triggering can be selected only by the TRIGGER menu key and is restricted to the single shot modes. The medium level is adjusted by the TRIGGER LEVEL knob. The trigger gap between positive and negative slope is adjusted by the TRACK knob. For line frequency related signals, a Line trigger source is available. The Line trigger source is selected by a softkey under the TRIGGER menu key. The External Trigger input provides an extra trigger input. This input can be used as the trigger source for the Main TimeBase (MTB) and Delayed Time Base (DTB). The input characteristics are simular to the input channels. To reduce the effect on triggering on noisy signals, trigger filters can be used. For this, lf-rej or hf-rej can be selected.

Refer to TRIGGER COUPLING and TRIGGER LEVEL for details.