Waveform capture rate measured by oscilloscope

In the measurement process, the high waveform capture rate is very important for the oscilloscope.Improves the ability of the oscilloscope to capture random events and low probability events.

Before describing the waveform capture rate, you must first understand the concept of dead time.

What isDead Zone Time? That is, the sum of the next collection and data processing time triggered by the oscilloscope during the two collection operations. The dead time may be longer and longer than the collection time. Shows a waveform capture cycle.

 

In, the captured dead zone time consists of a fixed dead zone time and a variable dead zone time. The fixed dead zone time depends on the architecture of each instrument. The variable dead zone time depends on the processing time, which is related to the set number of captured samples (record length), horizontal scale, sampling rate, and the selected post-processing functions (for example, interpolation, mathematical functions, measurement and analysis ).

If the dead time is too long, some key signal information may be lost. As shown in.

According to the following formula, if the waveform capture time (I .e., number of samples * Resolution, or 10 grid * horizontal scale), waveform capture rate, and probability of occurrence of a signal event have been determinedIncrease the measurement time to increase the probability of capturing and displaying signal events.

Where:

P: probability of capturing an accidental recurrence event [Unit: %]

Glitchrate: Signal failure frequency (for example, repeated pulse interference) [unit: 1/S]

T: Valid capture time or waveform display time (record length/sampling rate, or record length * Resolution, or 10 * time range/GRID) [unit: S]

Acqrate: waveform Capture Rate [unit: WfMS/S]

Tmeasure: measurement time, in seconds

 

The following is an example.

Example 1:

Assume that the glitch appears 10 times per second, the observation time window is 50ns (10 grids * 5ns/Div), and the observation time is 5 s.

The calculation is as follows:

(1) If the waveform capture rate is 1000 waveforms per second:

Dead Zone time % = (1ms-50ns)/1 Ms = 99.995%

Burr Capture Probability p = 100-100*(1-10 * 50ns) 1000*5 S = 0.25%

(2) If the waveform capture rate is 1 million waveforms per second:

Dead Zone time % = (1us-50ns)/1us = 95%

Burr Capture Probability p = 100-100*(1-10 * 50ns) 1000000*5 S = 91.8%

See.

Example 2:

Assume that a signal carries an exception that repeats 10 times per second. To display the signal on the oscilloscope, the horizontal scale is 10ns/Div. If the display screen has 10 horizontal grids, the effective capture time of 100ns can be calculated. To ensure that the confidence level of the event to be captured is high, a 99.9% probability is required. Now, the test time is determined by the waveform Capture Rate of the oscilloscope. The results are as follows:

Table 1 time required to capture duplicate abnormal signals

 

Therefore,The waveform capture rate is related to the settings of the horizontal scale, record length, and sampling rate.. In the actual measurement process, you need to find a balance point in these parameter settings based on the actual Tested signal, view the waveform with the highest capture probability, and improve the debugging efficiency.