|Figure 1: Using pass/fail testing to average only those|
waveforms which are inside the tolerance mask
Consider the example shown in Figure 1: To set up a selective average based on wave shape, one must create a tolerance mask using the Pass/Fail setup dialog box for condition Q1. In Figure 1, we see waveform C1 being tested against such a mask. If all points of the trace are inside the mask, the waveform is saved to memory M1. The oscilloscope's averager uses M1 as its source and accumulates only those pulses that match the tolerance mask.
|Figure 2: Selective averaging based on a Pass/Fail parameter|
limit. Only pulses with widths of less than 4.65 μs are
added to the average input.
This principle can be taken a bit further by averaging only pulses that meet the mask criteria as well as satisfying specific parameter limits. Pass/Fail testing supports up to eight criteria with a variety of logical combinations to initiate actions. Figure 2 shows an example of a similar selective-averaging setup. In this case, only pulses with a width of less than 4.65 μs are accumulated in the average.
In the Channel 1 trace of Figure 2, display persistence has been turned on so that the full range of pulse widths are displayed. Yet, note that only the pulses that meet the width criteria of less than 4.65 μs affect the average.
Hopefully, these examples give you an idea of the flexibility that selective averaging provides in an oscilloscope.