[Introduction]It is definitely unrealistic to stare at the oscilloscope screen for a long time to observe the occasional abnormal signal that is a headache. So, what are the efficient ways to capture such signals? Segmented storage, application born.
What is segmented storage
The segmented storage is triggered multiple times during the acquisition process, and the data sampled for each trigger is stored in a small storage that divides the storage space into segments.Oscilloscope trigger fills one segment at a time, idle signals or signals between segments are not interestingInteresting parts are not captured and stored.
The principle is shown in the figure below: the total storage depth is divided into n segments, the first segment is used for Display, and the second segment starts to store, that is, the data collected when the first trigger occurs is stored in the second segment storage space, when the After the second segment storage space is full, end the first trigger, wait for the second trigger, and store the data in the third segment storage space after triggering, and so on.
Segmented storage structure diagram
If the total storage depth of the oscilloscope is 512Mpts, the calculation formula of segment allocation is as follows:
N=512*1024*1024/[The current storage capacity is rounded to the power of 2n]-1
How to set up segmented storage
The maximum storage of ZDS5000 series oscilloscope is 512Mpts, while maintaining the sampling rate of 4GSa/s, it supports segmented storage range: 1~524287 segments. Click[Seg]by adjusting the time base gear, in the state of 560Kpts storage depth, it will be divided into 255 segments for storage and acquisition, as shown in the figure below.
Staging storage settings
Set the trigger mode to[Normal]adjust the trigger level to an appropriate position, and wait for a small probability abnormal signal to arrive.
By touching the probe with your finger, you can simulate the occurrence of a small probability abnormal signal. After the segment storage is completed, click[Stop]click[Current Segment]and you can view all segment storage by rotating the knob A/B, as shown in Figure 20.4. Waveform stored for segment 45.
segmented storage results
Segmented storage applications
1. Low duty cycle pulse or burst signal – there is a long idle time between signals. In many cases, even if there is a large storage, it is difficult to achieve the desired acquisition time by reducing the sampling rate. , and segmented storage can be done well.
Low duty cycle pulse signal
2. Serial bus analysis – The serial bus is transmitted in the form of data packets, and the idle time between packets will occupy the precious storage resources of the oscilloscope. With segmented storage, the oscilloscope can only collect data packets and not sample in idle time. . While maintaining a high sampling rate, more data packets can be collected to facilitate decoding and analysis.
Example application: 8-hour oscillation detection test
Take the ZDS5000 series oscilloscope to test the connector for vibration test as an example. During the whole test process, monitor the number of possible secondary failure areas of the connector, and then check whether the product is qualified.
1. Test requirements
The entire vibration test lasts 8 hours. During the whole process, the connector may have 0 to dozens of failures. The duration is more than 300ns, and the amplitude is uncertain (normally, the level is 1V).
2. Difficulties in testing
● The duration of the vibration test is 8 hours, and the oscilloscope is difficult to record waves based on a large time base, and the sampling rate is not enough;
● The vibration laboratory has large noise interference, and the peak waveform and clutter during failure are mixed together, so it is not easy to test the signal in the failure area.
For the above test problems, the segmented storage function of the ZDS5000 series oscilloscope provides a good solution.
First, according to the characteristics of the abnormal signal, set the trigger conditions for the oscilloscope to capture (including trigger level, trigger mode, time base, segment storage, number of segments, etc.), conduct 8-hour vibration test monitoring, and capture the abnormal situation as shown in the figure shown:
As shown in the figure, in the 8-hour test period, a total of 380,404 abnormal waveforms were captured. The above picture shows the abnormal situation and signal characteristics of the failure area of the 281st segment. The current sampling rate is still 4GSa/s.