Oscilloscope is one of the commonly used measuring instruments in electronic measurement. Today Xiaobian summarizes the common problems in the use of oscilloscope and the common problems in the purchase.
1. How to analyze the reliability of a designed product with an oscilloscope?
Answer: The oscilloscope has already become one of the most effective tools for detecting electronic circuits. By observing the voltage and current waveforms of key nodes of the circuit, you can intuitively check whether the circuit is working properly and verify whether the design is appropriate. This is extremely helpful for improving reliability. Of course, the correct analysis and judgment of the waveform depends on the engineer's own experience.
2. What are the main factors that determine the price of an oscilloscope probe?
Answer: There are many types of oscilloscope probes with different performances, such as high-voltage, differential, active high-speed probes, etc., and the price ranges from several hundred yuan to nearly ten thousand dollars. The main determinants of price are, of course, bandwidth and functionality. The probe is the part of the oscilloscope that contacts the circuit. A good probe can provide the fidelity required for testing. To do this, even passive probes must have a lot of passive component compensation circuits (RC networks) inside.
3. How long is the service life of a general oscilloscope probe? Does the probe need regular calibration?
Answer: The probe life of the oscilloscope is not easy to say, it depends on the use environment and method.
The standard does not have clear measurement regulations for probes, but for passive probes, at least when the probe is replaced and the probe exchanges channels, probe compensation adjustment must be performed. All active probes should be preheated for at least 20 minutes before use, and some active probes and current probes need to be adjusted for zero drift.
4. What is the real-time sampling rate of an oscilloscope?
Answer: The real-time sampling rate refers to the reciprocal of the sampling interval of one acquisition (one trigger) of the oscilloscope. It is understood that the highest level in the industry is the simultaneous use of four channels.
5. What is the equivalent time sampling of an oscilloscope?
Answer: Equivalent time sampling refers to the oscilloscope combining the waveforms collected by multiple acquisitions (multiple triggers) into one waveform. Each sampling rate may be very slow, and the trigger point of the two acquisitions will have a certain offset. The reciprocal of the minimum sampling interval between two points is called the equivalent sampling rate. The index can reach very high, such as 1ps.
6. What is power factor? How to measure?
Answer: Power factor: In a DC circuit, voltage times current is active power. But in an AC circuit, the voltage times the current is the apparent power, and part of the power that can work (ie, active power) will be less than the apparent power. The ratio of active power to apparent power is called power factor, which is expressed in COSΦ. In fact, the simplest measurement method is to measure the phase difference between voltage and current. The result is the power factor.
7. How to express and test the power density?
Answer: The power density is the power per unit volume, W / in3 is used in general power supply.
8. Is there a way to use an oscilloscope to measure the working condition of a high-frequency transformer or inductive core?
Answer: There is a function in the power test program launched by TEK-the analysis of BH curve, which can reflect the working state of the magnetic core, and can also measure the dynamic inductance value and obtain the core loss.
9. There are many kinds of noise caused by switching power supply, such as cross-interference caused by unreasonable wiring, inductance magnetic leakage, diode reverse spike ... etc., How to identify it with an oscilloscope?
Answer: TEK's TDS5000 oscilloscope can analyze the type of noise by analyzing the frequency domain of the frequency domain and analyzing the noise, so that the corresponding processing method can be used.
The oscilloscope can only provide data analysis and band-shaped display.
10. How can the oscilloscope test the radiation of the power supply at the beginning?
Answer: There is radiation interference in the switching power supply. The general approach is to try to detect the source of the interference and then shield it. The scope of Fourier transform can be used to analyze the frequency component composition with an oscilloscope, and the type of interference can be judged according to the frequency range.
Matters needing attention in use:
1. What is the fixed relationship between bandwidth and sampling frequency?
The sampling rate theoretically needs to meet the sampling law of agronomic fragrance, that is, at least 2 points per cycle of the highest frequency signal of the signal to be measured theoretically, otherwise it will cause aliasing. But in fact, it also depends on many other factors, such as waveform reconstruction algorithm, etc., Siglent series oscilloscopes use advanced waveform reconstruction algorithm, while equipped with interpolation algorithm to accurately reconstruct the waveform. Generally speaking, the sampling rate is 4-5 times the bandwidth to reproduce the waveform more accurately.
2. How to understand the bandwidth in oscilloscope specifications?
Bandwidth is the basic index of an oscilloscope. It is the same as the definition of the amplifier bandwidth. It is the so-called -3dB point. That is, the frequency point at which the sine wave is added to the oscilloscope input and the amplitude is reduced to 70.7% of the actual amplitude is called the bandwidth. In other words, using a 100MHz bandwidth oscilloscope to measure 1V, 100MHz sine wave, the amplitude is only 0.707V. This is still the case with sine waves. Therefore, when we choose an oscilloscope, in order to achieve a certain measurement accuracy, we should choose a bandwidth of 5 times the highest frequency of the signal. Siglent's ADS1000CE oscilloscope provides 300MHz bandwidth and 2GSa / a real-time sampling rate, leading the domestic counterparts.
3. Under the condition of a certain bandwidth, does the sampling frequency being too large have no meaning?
Bandwidth is the basic condition that limits the high-frequency components of the signal under test to be captured. Since Siglent oscilloscope adopts advanced waveform reconstruction algorithm and is equipped with interpolation algorithm display, it also provides a minimum real-time sampling rate of 500MS / s, which ensures perfect capture and true quantization of the trigger signal, and finally can accurately reproduce the acquired signal.
4. What are the factors that affect the working speed of the oscilloscope?
Simply put, the principle of the oscilloscope is similar. The front end is a data acquisition system, and the back end is processed by a computer. There are two main aspects that affect the speed of the oscilloscope. One is the data transmission from the front-end data acquisition to the back-end processing, which is generally transmitted by the bus, and the other is the back-end processing method. Siglent oscilloscope adopts mature high-speed hardware architecture and cooperates with DSP digital processing to effectively solve these bottlenecks and greatly improve the performance of the oscilloscope.
5. How to eliminate glitches when using an oscilloscope?
If the glitch is inherent in the signal itself, and you want to use edge trigger to synchronize the signal (such as a sinusoidal signal), you can use the high frequency suppression trigger method, which can usually synchronize the signal. If the signal itself has a glitch, but it is usually difficult for the oscilloscope to consider removing the glitch without displaying the glitch. You can try to use the method of limiting bandwidth, but accidentally may also consider part of the signal itself.
Sixth, when choosing an oscilloscope, bandwidth is generally considered. So, under what circumstances should the sampling rate be considered?
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 also has some empirical formulas for sampling rate, but basically all are derived for the bandwidth of the oscilloscope. In practical applications, it is best not to use the oscilloscope to measure the signal at the bandwidth frequency.
If you are selecting a model, for a sine wave, choose an oscilloscope whose bandwidth is more than 3 times the frequency of the measured sine signal, and the sampling rate is 4 to 5 times the bandwidth, actually 12 to 15 times the signal. 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), the sampling rate is insufficient, otherwise the measurement accuracy is not satisfied. of. You can also use the dot display to analyze whether the sampling rate is sufficient. Professional Siglent series oscilloscopes have solved the problems of bandwidth and sampling rate.
7. When analog and digital oscilloscopes observe the details of the waveform, which one is more advantageous?
The vertical accuracy of analog oscilloscopes we used in the early days is generally +/- 3%, while the vertical accuracy of digital oscilloscopes is as high as +/- 1%. In this regard, digital oscilloscopes should have great advantages. At the same time, Siglent digital oscilloscope has different levels of brightness options, which is more convenient and intuitive for displaying signal details.
8. How to capture and reproduce the instantaneous signal that disappears?
To capture the instantaneous signal, refer to the following settings: the trigger type selects the edge, the trigger mode is set to a single mode, the signal is set to rising trigger, and the trigger level is adjusted to an appropriate value. In addition, the Siglent oscilloscope is equipped with EasyZoom window extension technology, that is, it can observe the local details while zooming in on the global signal.
9. What type of oscilloscope can effectively improve the design efficiency?
With the development of oscilloscopes to the present day, data analysis and processing have been greatly improved. Using oscilloscope is not only to observe the waveform during debugging, but more importantly, it can find the problem well in the design, analyze and calculate the device parameters, and help you optimize the design plan. Which oscilloscope to choose is the most suitable to be combined with the signal you want to observe and decide. Siglent high-performance oscilloscopes provide 25M ---- 300M bandwidth and 500MSa / s --- 2GSa / s sampling rate to meet your different needs.
10. What should the probe pay attention to when using the oscilloscope?
Probes are often overlooked in the use of oscilloscopes. Passive probes are widely used because of their wide measurement range and low price, and they can meet most measurement requirements. Passive probe probes should be selected in accordance with the bandwidth of the scope. When the probe is replaced and the probe exchanges channels, the probe compensation adjustment must be performed to match the input channel. The simplest and most intuitive way to adjust the probe compensation is to use the probe waveform.
11. What is the real-time sampling rate of an oscilloscope?
Real-time sampling refers to sampling the waveform at equal time intervals, performing A / D conversion in the order of sampling and storing it in memory. Real-time sampling is the most obvious and intuitive sampling method. This type of sampling only needs to be simple in time Distributed sampling points, all sampling points are obtained in response to a trigger of the oscilloscope. Siglent high-performance oscilloscope provides real-time sampling rate of 500MSa / s --- 2GSa / s.
12. What is the equivalent time sampling of an oscilloscope?
Equivalent time sampling refers to the waveform that the oscilloscope collects from multiple acquisitions (multiple triggers) to form a waveform. Each sampling rate may be very slow. There is a certain offset between the trigger points of the two acquisitions. The reciprocal of the minimum sampling interval between points is called the equivalent sampling rate. The index can reach very high, such as 1ps. Equivalent sampling of Siglent high-performance oscilloscopes up to 50Sa / s
13. When looking at the waveform on the oscilloscope, what is the difference between using external trigger and self-triggering?
The usual trigger of an oscilloscope is edge trigger. There are two trigger conditions, trigger level and trigger edge; that is, when the rising edge (or falling edge) of the signal reaches a certain level (trigger level), the oscilloscope triggers.
The oscilloscope will use external trigger only when there is a problem with the signal's self-triggering. There is no better problem. In addition, the signal is more complicated, there are many points that meet the trigger condition, and it cannot be triggered at the same position every time, so as to obtain a stable display. At this time, you need to use external trigger. SiglentADS1000 oscilloscope provides standard dual channel + one external trigger channel
14. How to obtain the total bandwidth of the measurement system?
When measuring digital signals, the rise time of the signal determines the total bandwidth of the system, the total bandwidth of the measurement system = 0.35 / rise time
15. How to apply trigger relief in measurement? What does it do?
The meaning of trigger holdoff is to temporarily close the trigger circuit of the oscilloscope for a period of time (ie holdoff time). During this time, the oscilloscope will not trigger even if there are signal waveform points that meet the trigger conditions. Stable waveform display, trigger holdoff is also a function set for stable waveform display. It is mainly set for the repetition of a large period and there are many non-repeated waveform points that meet the trigger condition in the large period. Siglent oscilloscope provides a very long trigger hold-off time of 100ns--1.5s.
16. The oscilloscope is normal, but when the oscilloscope is used to observe the signal under test, the waveform is disordered. How to solve it?
The reason for this is that the ground of the signal under test does not share the ground of the oscilloscope. Usually, the self-test signal of the oscilloscope is used to check whether the probe and the oscilloscope are normal. If the oscilloscope and the probe are normal, the measured waveform is abnormal. When measuring a signal with a small amplitude, you can unplug the ground wire of the probe (the ground wire is equivalent to an antenna, which interferes with small signals). Use a near-earth wire connected to the Siglent oscilloscope for testing. To eliminate false triggering caused by noise, the "acquisition method" can be selected as "average".
17. The oscilloscope is normal and can see the scan line, but no signal waveform is generated when observing the signal under test?
Three reasons:
1. Input signal from channel 1, but channel 2 is accidentally opened;
2. Select the signal coupling mode (AC-GND-DC) at the grounding position.
3. Confirm that the signal has been generated and is normally input to the oscilloscope BNC interface
18. How to measure DC voltage?
First, you need to set the coupling mode to DC, adjust the vertical scale to an appropriate value according to the approximate range, and then compare the displacement of the offset line and the channel mark. Siglent series oscilloscopes use the only domestic algorithm that can identify DC, and automatically identify and test DC voltage signals. Press "AUTO" automatic measurement to complete the test results during use.
19. Why does the waveform storage already store the settings, and what is the purpose of storing the settings?
First of all, the main difference between the two is that the storage space occupied by waveform storage is much larger than the set storage space. Therefore, considering the space and cost of the memory, you need to save the two separately. Secondly, there are also differences in the transfer of the two. The waveform is recalled. The oscilloscope is in the STOP state. The saved running state is not changed when the recall is set, which makes it convenient to observe the waveform directly.
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