With the development of computer, semiconductor and communication technology, the oscilloscope, which has been a good helper in the design and debugging of products, has become more and more widely used in electronics. If you want to accurately and quickly perform system signal in the use of oscilloscope Analysis, there are many new factors that must be considered when measuring: for example, whether the speed of the instrument can keep up with the change of the signal under test, whether the bandwidth is sufficient, whether the measurement method will introduce interference, and even the probe used Is it suitable, etc. These are some of the common problems in the use of oscilloscopes. How do we deal with these problems when we encounter them? Let me tell you how to deal with the common problems of oscilloscopes:
Question 1: When choosing an oscilloscope, bandwidth is generally considered the most, so under what circumstances should the sampling rate be considered?
Answer: The bandwidth depends on the measured object. On the premise of satisfying the bandwidth, I hope that the minimum sampling interval (reciprocal of the sampling rate) can capture the signal details you need. The industry has some empirical formulas about sampling rate, but they are basically derived from the bandwidth of the oscilloscope. In practical applications, it is best not to use an oscilloscope to measure signals of the same frequency. When selecting the model, the oscilloscope bandwidth for the sine wave should be more than 3 times the frequency of the measured sine signal, and the sampling rate is 4 to 5 times the bandwidth, which is actually 12 to 15 times the signal; if it is other waveforms, Make sure 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 by stopping the waveform and zooming in on the waveform. If you find that the waveform changes (such as certain amplitudes), it means that the sampling rate is not enough, otherwise there is no harm. You can also use the dot display to analyze whether the sampling rate is sufficient.
Question 2: Why does my oscilloscope sometimes fail to capture the amplified current signal?
Answer: If the signal does exist, but the oscilloscope can sometimes catch or sometimes not, it may be related to the setting of the oscilloscope. Generally, you can set the oscilloscope trigger mode to Normal, set the trigger condition to edge trigger, adjust the trigger level to an appropriate value, and then set the sweep mode to single mode. If this does not work, it may be a problem with the instrument.
Question 3: Some instantaneous signals are lost, how to capture and reproduce them?
Answer: Set the oscilloscope to single acquisition mode (the trigger mode is set to Normal, the trigger condition is set to edge trigger, and the trigger level is adjusted to an appropriate value, and then the scan mode is set to single mode), pay attention to the storage depth of the oscilloscope It will determine when you can acquire the signal and the maximum sampling rate you can use.
Question 4: How to measure power supply ripple?
Answer: You can use the oscilloscope to capture the entire waveform first, and then enlarge the part of the ripple of interest to observe and measure (either automatic measurement or cursor measurement), and also use the FFT function of the oscilloscope to analyze from the frequency domain.
Question 5: Questions about the comparison between analog and digital oscilloscopes: 1. Which of the analog and digital oscilloscopes has the advantage when observing the details of the waveform (for example, at zero crossings and peaks, observe less than 1% of parasitic waveforms)? 2. Digital oscilloscope Generally provide online display rms value, what is its accuracy?
Answer: 1) Observe the parasitic waveform below 1%. Whether it is an analog oscilloscope or a digital oscilloscope, the observation accuracy is not very good. The vertical accuracy of an analog oscilloscope may not be higher than that of a digital oscilloscope. For example, the vertical accuracy of an analog oscilloscope with a bandwidth of 500 MHz is ± 3%, which is no higher than that of a digital oscilloscope.
(Usually the accuracy is 1-2%) It has more advantages, and for details, the automatic measurement function of the digital oscilloscope is more accurate than the manual measurement of the analog oscilloscope.
2) For the accuracy of the amplitude measurement of the oscilloscope, many people use A / D digits to measure. In fact, it will change with the bandwidth of the oscilloscope you are using, the actual sampling rate settings, etc. If the bandwidth is not enough, the amplitude measurement error itself will be very large. If the bandwidth is enough, the sampling setting is very high, and the actual amplitude measurement accuracy is not as good as the accuracy when the sampling rate is low (you can sometimes refer to the oscilloscope user manual, It may give the actual effective number of A / D digits of the oscilloscope under different sampling rates). In general, the accuracy of the oscilloscope to measure the amplitude, including the root mean square value, is often not as good as that of a multimeter. Similarly, it is not as good as a frequency counter for measuring frequency.
Question 6: Each oscilloscope has a frequency range, such as 10M, 60M, 100M ... the oscilloscope I use is nominally 60MHz, can it be understood that it can measure up to 60MHz? Can I use it to measure 4.1943MHz The square wave is not detected, what is the reason?
Answer: A 60MHz bandwidth oscilloscope does not mean that a 60MHz signal can be measured well. According to the definition of the oscilloscope bandwidth, if you input a 60MHz sine wave with a peak-to-peak value of 1V to a 60MHz bandwidth oscilloscope, you will see a 0.707V signal (30% amplitude measurement error) on the oscilloscope. If you test a square wave, the reference standard for selecting an oscilloscope should be the signal rise time, the oscilloscope bandwidth = 0.35 / signal rise time × 3, and your rise time measurement error is about 5.4%. The measurement error is about 5.4%.
The bandwidth of the oscilloscope probe is also very important. If the oscilloscope probe used includes a system bandwidth consisting of front-end accessories, the bandwidth of the oscilloscope will be greatly reduced. If you use a 20MHz bandwidth probe, the maximum bandwidth that can be achieved is 20MHz. If you use a connecting wire at the front of the probe, it will further reduce the performance of the probe, but it should not have much impact on the square wave around 4MHz, because the speed is not very fast.
Also take a look at the oscilloscope user manual. Some 60MHz oscilloscopes will have their actual bandwidth sharply reduced to below 6MHz at a 1: 1 setting. For a square wave around 4MHz, the third harmonic is 12MHz and the fifth harmonic is 20MHz If the bandwidth is reduced to 6MHz, the amplitude of the signal is greatly attenuated. Even if the signal can be seen, it is definitely not a square wave, but a sine wave whose amplitude is attenuated. Of course, there are many reasons why the signal cannot be measured. For example, the probe is not in good contact (this phenomenon is easy to rule out). It is recommended to use a BNC cable to connect a function generator to check whether the oscilloscope itself has any problems. The probe has no problems, such as If you have any questions, please contact the manufacturer directly.
Question 7: Some instantaneous signals are lost, how to capture and reproduce them?
Answer: Set the oscilloscope to single acquisition mode (the trigger mode is set to Normal, the trigger condition is set to edge trigger, and the trigger level is adjusted to an appropriate value, and then the scan mode is set to single mode), pay attention to the storage depth of the oscilloscope It will determine when you can acquire the signal and the maximum sampling rate you can use.
Question 8: How to understand "when the sampling rate of the evaluation waveform is not enough, stop the waveform and zoom in on the waveform. If the waveform is found to have changes (such as certain amplitudes), it means that the sampling rate is not enough, otherwise it is not harmful. It can also be displayed by points. Is it sufficient to analyze the sampling rate? "
Answer: I had the honour to do the actual measurement for the user and experienced this phenomenon. At the time, the measured object was a random-looking and high-speed changing signal. The user set the trigger level to about -13V. When I wanted to zoom in on the measurement details after the waveform was collected, I found that when I changed the oscilloscope time base (SEC / DIV) setting, the signal amplitude suddenly became smaller. I changed the oscilloscope to a point display at the time and found that the number of points (memory depth) was not enough. But after comparing the dot display and the vector display, I found that if the vector display has a certain credibility, then the signal is abrupt in the current two sampling intervals (reciprocal of the sampling rate), but it cannot be collected (the sampling interval is not fine enough) , That is, the sampling rate is not high enough). I changed to an oscilloscope with the same storage depth but a higher sampling rate, and found that the problem disappeared.
Storage depth also affects the actual maximum sampling rate that the oscilloscope can use. If the storage depth is too shallow, it may be a problem, because the storage depth may limit the maximum sampling rate that can be actually used, but in essence the sampling rate is not enough, and signal details are lost. If the storage depth is not deep enough, the actual sampling rate may not be high, which has little to do with the indicators provided by the manufacturer.
Kids Nylon Raincoat, Nylon Raincoat, Childrens Nylon Raincoat
Zhejiang CC Industrial And Trading Co., Ltd , http://www.ccraincoats.com