Patent US 4,901,009

In a digital oscilloscope, the recording of transients exceeding a predetermined tolerance range is to be provided by simple means. A method and a device for carrying out this method are provided in which two envelope curves are stored in an envelope curve memory and these are then compared with cyclically repetitive amplitude samples of a signal curve. A trigger signal ensures that the signal curve containing the disturbance is served if one of the signal curves exceeds the tolerance range delimited by the envelope curves, which is the case, in particular, when interference signals occur. This curve can then be displayed for analysis on the screen. The invention can be applied within the context of digital measuring technology wherever signal curves are recorded and instantaneous disturbances must be detected.