Common Problems in Using Digital Oscilloscopes

1. How to measure DC voltage?  

Answer: You need to set the coupling mode to DC, adjust the vertical scale to a suitable value according to the approximate range, and then compare the displacement of the offset line and the channel mark.  

2. Users reported that the amplitude exceeded the screen range when measuring 220V AC power? How to measure the phase difference of three-phase power?  
  
Answer: The maximum input peak-to-peak voltage of the DS5000 series is 400V. According to the peak-to-peak conversion formula of the effective value, the 220V AC power exceeds the 400V peak-to-peak value. It is normal for the amplitude to exceed the screen range. When using an oscilloscope to measure the phase shift of a three-phase power supply, you can set the trigger source to AC power, and use one channel to measure the AB waveform first, then store it as a reference waveform, and then use the probe to connect BC. At this time, the phase shift can be measured.  

3. What is aliasing suppression?  
  
Answer: Aliasing refers to a condition caused by the acquisition frequency of the oscilloscope being lower than 2 times the maximum frequency of the actual signal. Aliasing suppression is specially designed to prevent the generation of aliasing. Aliasing suppression can determine the maximum frequency of the signal and acquire the signal at 2 times the maximum frequency.  

4. How to capture non-periodic signals?

Answer: ①. Set the trigger level to the required value. ②. Click the main control button SINGLE, the machine starts waiting. If a certain signal reaches the set trigger level, it will be sampled once and displayed on the screen. This function can easily capture accidental events, such as sudden glitches with large amplitude: set the trigger level to just above the normal signal level, click the SINGLE button, and when the glitch occurs, the machine will automatically trigger and record the waveform before and after the trigger. Drag the trigger position mark line to get negative delay triggers of different lengths, which is convenient for observing the waveform before the glitch occurs.  

5. How to observe the noise of low-voltage DC power supply?  
  
Answer: ①. Connect the oscilloscope probe between channel A1 (or A2) and the measured point. ②. Set the trigger source (Trigger Source) to A1 or A2 (must be consistent with the channel of the actual measured signal input). ③. Click the A1 or A2 button and select the coupling mode as AC (alternating current) coupling. ④. Adjust the sampling rate and vertical sensitivity until a satisfactory display is obtained.   

6. In what occasions can the acquisition method of the DS5000 oscilloscope be applied?  

Answer: To observe a single signal, please use the real-time sampling mode. To observe a high-frequency periodic signal, you can use the equivalent sampling mode. To observe the envelope of the signal to avoid confusion, please use the peak detection mode. To reduce the random noise in the displayed signal, please use the average sampling mode. The number of average values ​​can be selected. To observe a low-frequency signal, select the rolling mode. To display a waveform close to the effect of an analog oscilloscope, please use the analog acquisition mode.  

7. What is the relationship between triggering and waveform acquisition?  
  
Answer: For different types of oscilloscopes and different capture modes of the oscilloscope, the relationship between triggering and waveform acquisition is different. If it is the equivalent time sampling mode of a sampling oscilloscope or a real-time oscilloscope, the acquisition of a waveform requires multiple triggers. For the real-time sampling mode of a real-time oscilloscope, the waveform will definitely be acquired once when it is triggered. If it is not triggered, the waveform may also be acquired. This is the AUTO mode of the trigger. (There are three trigger modes, one is AUTO. If it is not triggered, the waveform will be refreshed, but the waveform will be unstable on the screen. The other is NORMAL, which is refreshed only when it is triggered. The last one is SINGLE. The waveform is captured for the first time, and it will not be captured in the future.).  

8. Can RIGOL products automatically generate an EXCEL table after saving the waveform data?  
   
Answer: Yes. Ultrascope software can automatically save the waveform data after downloading in the file format of an Excel table. The RVO virtual instrument does not have the function of automatically generating an Excel table in the software, but we provide a conversion tool (free download is available on the official homepage of RIGOL, the software name is: DatKit for RVO3000&4000 Series). This tool can be used to convert the RVO file format saved in "*.dat" to the text file format of "*.txt". Modify txt to xls to save the data in an Excel table.  

9. After collecting the signal, the waveform of the signal does not appear on the screen. How to deal with it?  

Answer: You can check and deal with it according to the following steps: 1. Check whether the probe is normally connected to the signal connection line; 2. Check whether the signal connection line is normally connected to the BNC (i.e. channel connector); 3. Check whether the probe is normally connected to the object under test; 4. Check whether the object under test has any signal generated (you can connect the channel with the problematic channel together to determine the problem). 5. Collect the signal again.   

10. What are the applications of glitch/pulse width triggering?  

Answer: There are two typical applications of glitch/pulse width triggering. One is to synchronize circuit behavior, such as using it to synchronize serial signals, or for applications with very serious interference, it is impossible to use edge triggering to correctly synchronize signals. Pulse width triggering is an option; the other is to find abnormal phenomena in the signal, such as narrow glitches caused by interference or competition. Since the abnormality is sporadic, it must be captured by glitch triggering (another method is peak detection, but the peak detection method may be limited by its maximum sampling rate. At the same time, it can generally be seen but not measured). If the pulse width of the object under test is 50ns, and there is no problem with the signal, that is, there is no signal distortion or narrower caused by interference, competition, etc., the signal can be synchronized with edge triggering without using glitch triggering. 11.  

When choosing an oscilloscope, the bandwidth is generally considered the most. Under what circumstances should the sampling rate be considered?  

Answer: It depends on the object under test. Under the premise of meeting the bandwidth, it is hoped that the minimum sampling interval (the inverse of the sampling rate) can capture the signal details you need. There are some empirical formulas for sampling rate in the industry, but they are basically derived for the bandwidth of the oscilloscope. In practical applications, it is best not to use an oscilloscope to measure signals of the same frequency. If you are selecting a model, for a sine wave, choose an oscilloscope with a bandwidth that is 3 times the frequency of the sine signal being measured. If the bandwidth is above 3 times, the sampling rate is 4 to 5 times the bandwidth, which is actually 12 to 15 times the signal. For other waveforms, ensure that the sampling rate is sufficient to capture signal details. If you are using an oscilloscope, you can verify whether the sampling rate is sufficient through the following methods: Stop the waveform and zoom in on the waveform. If you find that the waveform has changed (such as certain amplitudes), the sampling rate is not enough, otherwise it is fine. You can also use point display to analyze whether the sampling rate is sufficient.   

12. How to eliminate glitches when using an oscilloscope?  

Answer: If the glitches are inherent in the signal itself, and you want to synchronize the signal (such as a sine signal) with an edge trigger, you can use the high-frequency suppression trigger mode, which can usually synchronize the signal. If the signal itself has glitches, but you want the oscilloscope to eliminate the glitches and not display the glitches, it is usually difficult to do so. You can try to use the method of limiting bandwidth, but if you are not careful, you may also filter out part of the information of the signal itself. If you use a logic analyzer, generally speaking, using the state acquisition method, some glitches collected in the timing mode will not be visible.  

13. What are the various trigger applications of the DS5000 oscilloscope, such as edge trigger, pulse width trigger and video trigger? Which signal are they suitable for?  
  
Answer: Edge trigger, you can set the trigger level, rising edge or falling edge. Edge trigger is also called basic trigger. Pulse width trigger, you can determine the trigger time according to the pulse width. You can capture abnormal pulses by setting the pulse width condition. Video trigger, you can trigger on the field or line of NTSC, PAL or SECAM standard video signal.  

14. Using the DS5000 series oscilloscope, how can you completely capture and save a one-time random signal, and then replay it for analysis?  
  
A: If the so-called random signal being measured is a single signal, then you only need to set the vertical and horizontal scales that match the signal, adjust the trigger level, use a single trigger and wait for the signal to appear, and then use the waveform saving function of the storage type of STORAGE to store the captured waveform. If you need to replay the saved waveform, you only need to call out the waveform to replay the analysis.  

15. Why is it useful to store the settings when the waveform storage has already stored the settings?  

A: First of all, the main difference between the two is that the storage space occupied by the waveform storage is much larger than the setting storage space. Therefore, considering the storage space and cost, the two need to be saved separately. Secondly, there are also differences in the call-out of the two. When the waveform is called out, the oscilloscope is in the STOP state. When the settings are called out, the saved running state is not changed, which makes it convenient to directly observe the waveform.