Answers to the basic knowledge and usage of Tektronix oscilloscopes

 

    A: Oscilloscopes have long been one of the most effective tools for testing electronic circuits. By observing the voltage and current waveforms at key nodes of the circuit, one can visually check whether the circuit is working properly and verify whether the design is appropriate. This is extremely helpful in 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?

 

    A: There are many types of oscilloscope probes with different performances, such as high voltage, differential, active high-speed probes, etc. The price ranges from a few hundred RMB to nearly $10,000. The main determinants of price are of course bandwidth and function. The probe is the part of the oscilloscope that contacts the circuit. A good probe can provide the fidelity required for testing. To achieve this, even a passive probe must have a lot of passive device compensation circuits and RC networks inside.

 

    3. How long is the service life of a general oscilloscope probe? Does the probe need to be calibrated regularly?

 

    A: It is hard to say how long the oscilloscope probe will last, as it depends on the environment and method of use. The standard does not have clear measurement regulations for oscilloscope probes, but for passive probes, at least when replacing the probe or switching 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 require zero drift adjustment.

 

    4. What is the real-time sampling rate of an oscilloscope?

 

    A: The real-time sampling rate refers to the reciprocal of the sampling interval of the oscilloscope collecting and triggering once. It is understood that the highest level in the industry is the simultaneous use of four channels.

 

    5. What is equivalent time sampling of an oscilloscope?

 

    A: Equivalent time sampling means that the oscilloscope combines waveforms collected by multiple acquisitions and multiple triggers into one waveform. The sampling rate may be very slow each time, and there is a certain offset between the two acquisition trigger points. The inverse of the minimum sampling interval between the two points is called the equivalent sampling rate. Its index can be very high, such as 1ps.

 

    6. What is power factor? How to measure it?

 

    Answer: Power factor: In a DC circuit, voltage multiplied by current is active power. But in an AC circuit, voltage multiplied by current is apparent power, and the part of power that can do work (i.e. active power) will be less than the apparent power. The ratio of active power to apparent power is called power factor, which is represented by COSΦ. In fact, the simplest way to measure it is to measure the phase difference between voltage and current, and the result is the power factor.

 

    7. How to express and test power density?

 

    Answer: Power density is the power per unit volume, and W/in3 is generally used in power supplies.

 

    8. Is there any way to use an oscilloscope to measure the working condition of a high-frequency transformer or inductor core?

 

    Answer: The power test solution launched by TEK has a function - BH curve analysis, which can reflect the working status of the magnetic core, measure the dynamic inductance value, and derive the core loss.

 

    9. There are many types of noise in switching power supplies, such as cross interference caused by unreasonable wiring, inductor leakage, diode reverse spikes, etc. How to identify them with an oscilloscope?

 

    A: TEK's TDS5000 oscilloscope has frequency domain analysis. By analyzing the frequency band of the noise, the type of noise can be analyzed, and the corresponding processing method can be used. The oscilloscope can only provide data analysis and band shape display.

 

    10. How can I use an oscilloscope to test the radiation of the power supply?

 

    A: Switching power supplies have radiated interference. The general approach is to find out the source of interference and then shield it. An oscilloscope can be used to analyze its frequency component composition through Fourier transform function, and the type of interference can be determined based on the frequency range.

 

    数字示波器是具有波形触发、存储、显示、测量、波形数据分析处理等独特优点，其使用日益普及。由于数字示波器与模拟示波器之间存在较大的性能差异，如果使用不当，会产生较大的测量误差，从而影响测试任务。请看一下沈阳众博铭诚科技有限公司对数字示波器的操作的详细介绍：

 

    With the development of electronic technology, digital oscilloscopes have greatly expanded their working capabilities with digital technology and software. The shortcomings of early products such as low sampling rate, large dead time, and low screen refresh rate have been greatly improved. Modulated signals, communication eye diagrams, video signals and other composite signals that were previously difficult to observe are becoming easier to observe. Digital oscilloscopes can calculate and analyze data, and are particularly suitable for capturing all the details and abnormal phenomena generated in complex dynamic signals. Therefore, they have been widely used in scientific research and industrial production. In order to make the digital oscilloscope work in a qualified state, it is an urgent task for test engineers to regularly, quickly and comprehensively calibrate the oscilloscope to ensure its traceability.

 

    Manual calibration is inefficient and prone to errors. The calibration of each oscilloscope requires test engineers to read a lot of information. The automatic test system has the characteristics of accurate and fast parameter measurement, intuitive display of test results, and automatic storage of test data, which are unattainable by traditional manual testing. Using the automatic test system to realize program-controlled calibration of oscilloscopes will be the trend of instrument calibration.

 

    GPIB, VXI, and PXI are standard buses for automatic test systems. GPIB has won the recognition of users for its stable performance, convenient operation, and low price. Here, GPIB is selected as the bus of the test system.

 

    Distinguish between analog bandwidth and digital real-time bandwidth. Bandwidth is one of the most important indicators of digital oscilloscopes. The bandwidth of an analog oscilloscope is a fixed value, while the bandwidth of a digital oscilloscope has two types: analog bandwidth and digital real-time bandwidth. The highest bandwidth that a digital oscilloscope can achieve for a repetitive signal using sequential sampling or random sampling technology is the digital real-time bandwidth of the oscilloscope. The digital real-time bandwidth is related to the highest digitization frequency and the waveform reconstruction technology factor K (digital real-time bandwidth = highest digitization rate/K), and is generally not given directly as an indicator. From the definitions of the two bandwidths, it can be seen that the analog bandwidth is only suitable for the measurement of repetitive periodic signals, while the digital real-time bandwidth is suitable for the measurement of both repetitive signals and single signals. When the manufacturer claims that the bandwidth of the oscilloscope can reach a certain number of megabytes, it actually refers to the analog bandwidth, and the digital real-time bandwidth is lower than this value.