An improved delayed sweep system is disclosed for an oscilloscope having main and delayed sweeps. A trigger pickoff circuit has means for providing a pair of pre-selected trigger pickoff points on the delaying sweep so that delayed sweeps may be generated in accordance with the two points selected. An alternating display mode facilitates presentation of the delaying sweep and both delayed sweeps in a single display, with the relative time positions of both delayed sweeps appearing on the delaying sweep as a pair of intensified zones. Either delay time measurement between the sweep start and a point of interest on the display, or differential time measurement between two points of interest on the display may be made. Voltages proportional to the selected time measurement may be applied to a properly scaled digital voltmeter to provide a direct readout in units of time.

An oscilloscope is provided with a dual time base system in which the nonlinear startup segment of the main sweep is eliminated before delay time comparison, thereby facilitating accurate differential measurements down to and including the triggering event (zero time). System delays are built in to ensure that the displayed sweep trace also begins at the left edge of the viewing screen, and, moreover, the triggering event may be viewed on both the main and delayed sweeps. The built-in system delays may be programmable to facilitate delay matching of vertical channels or time matching of independent sweep operation.

A triggerable oscilloscope having a digital clock selectably connected to two digital counters accurately measures a time interval between two recurring events. The first digital counter is connected to the digital clock to count clock pulses during a timer interval between the initiation of a horizontal sweep signal and the occurrence of the first recurring event. A second digital counter is connected to the digital clock to count clock pulses during a time interval between the initiation of a sequent horizontal sweep signal and the occurrence of the second recurring event. A subtractor circuit coupled to the first and second digital counters subtracts the count of the first digital counter from the count of the second digital counter and determines the time interval between the first and second recurring events. Time averaging techniques increase the accuracy of the time interval measurements for high speed recurring events by accumulating counts during a plurality of horizontal sweep signals. Predivide techniques are used for low speed recurring events to limit the number of counts accumulated during a horizontal sweep signal to a number compatible with the capacity of the digital counters.

The sweep trigger pulses generated internally in an oscilloscope are coupled to a pulse counter, which counter is reset periodically and a number proportional to the count accumulated during each period is displayed.

Apparatus for measuring the time integral of a signal between pairs of time points comprises a ramp voltage generator and a plurality of pairs of potentiometers. A comparator circuit is associated with each potentiometer to provide a switching signal at the time point when the ramp voltage becomes equal to the potentiometer voltage. The switching signals are applied to a gate which is held open between each pair of time points to allow the signal to be measured to be passed to a suitable measuring means. Such measuring means may comprise a voltage-to-frequency converter and a counter so that the output of the counter represents the time integral of the signal.