How to Choose a Suitable Oscilloscope in University Laboratories

As a basic test instrument, the oscilloscope was once a pet in university laboratories. At that time, 20 to 30 students in a laboratory gathered around an oscilloscope to listen to the teacher's explanation and conduct tests. With the substantial improvement of China's economic strength and the strong support of the state for education, oscilloscopes have now become a must-have instrument for electronic laboratories in universities. Even in many vocational education colleges, there are many oscilloscopes of different grades. Faced with the numerous oscilloscopes on the market, how to choose the right product according to the measurement needs of the laboratory has become an urgent problem facing many universities. The

current status of the oscilloscope industry

Oscilloscopes are mainly divided into two categories: analog oscilloscopes and digital storage oscilloscopes.

1. The current status of analog oscilloscopes. At present, the main manufacturers of analog oscilloscopes are showing a trend of gradual reduction. The United States has stopped the production of analog oscilloscopes since the mid-1990s, and there are only 2-3 left in Japan. There are still about 10 in China.

At present, analog oscilloscopes are mainly used in laboratories, production lines, maintenance and testing in some special fields of universities.

Since analog oscilloscopes have more important brightness information in three-dimensional display and a refresh rate of up to hundreds of thousands of times, analog oscilloscopes have infinite resolution in time, that is, the measurement of input signals by analog oscilloscopes is continuous in time. Therefore, low-end digital oscilloscopes cannot completely replace analog oscilloscopes.

2. Current status of digital storage oscilloscopes: The main manufacturers are Agilent, Tektronix and LeCroy in the United States. Goodwill in Taiwan and Beijing Puyuan Precision Electronics, which has emerged in China.

Since digital oscilloscopes contain many technical indicators, many customers cannot find their reasonable needs among the many indicators. The

main technical indicators of digital oscilloscopes: bandwidth, sampling rate, storage depth and waveform update rate

Bandwidth: In order to ensure the accuracy of the amplitude and rising edge of the test signal, the bandwidth of the selected oscilloscope should be 3-5 times the frequency of the measured signal, and 8-10 times or more for accurate measurement.

Sampling rate and storage depth: The sampling rate given by the general manufacturer is the maximum value, that is, the sampling rate achieved under the fastest scanning time. However, in actual measurement, the sampling rate is a variable indicator. As the scanning time slows down, the sampling rate also decreases accordingly. So its actual value depends on the time base and storage depth.

Sampling rate [MS/S] * [time/grid × 10 grids] = storage depth

DSO needs to sample the input signal, convert it to analog-to-digital, send it to the memory and perform relevant processing, and then display it after digital-to-analog conversion. In addition, since the waveform update rate of ordinary digital oscilloscopes is relatively low (about 100 times/second-10,000 times/second), confusion is inevitable in actual testing. Therefore, when choosing a digital storage oscilloscope, it is not only necessary to look at the technical indicators, but more importantly, the actual measurement of complex signals. It is not difficult to see from

the main digital storage oscilloscope manufacturers and product specifications

that in the digital storage oscilloscope industry, the three major American companies are far ahead in both technology and market share. However, the emergence of Puyuan Jingke has revitalized the domestic oscilloscope industry after a decade of stagnation. Recently, they have just launched an oscilloscope with a bandwidth of 200MHz, a sampling rate of 1GS/S, and a storage depth of 1M. For such a company composed of young people, new recruits in the industry, I believe they will give us more wonderful products.

The current situation of oscilloscopes in colleges and universities

At present, the use of oscilloscopes in colleges and universities is mainly concentrated in physical experiment centers, electrical and electronic experiment centers and information professional laboratories.

Physical experiment centers generally use 20MHz dual-channel analog oscilloscopes.
Electrical and electronic experiment centers mainly include analog circuit laboratories, digital circuit laboratories, electrical laboratories, EDA laboratories, and PLC laboratories. The instruments used by various colleges and universities are not the same.

Overall, there are the following problems in the use of oscilloscopes in college laboratories:

1. There is no standard calibrator. As an instrument for quantitative observation, it is difficult for the laboratory to judge the accurate indicators of the oscilloscope. It is not enough to do some simple tests with ordinary function sources. There was once a customer who used a 6MHz function signal generator to output a 6MHz sine wave with an amplitude of 4mV to evaluate three different models of 20MHz oscilloscopes. It was found that one of the test results had burrs on the sine wave, and the waveforms of the other two looked smooth when observed. Therefore, the customer thinks that the oscilloscope with burrs has problems, and the one without burrs is good. In fact, this is a problem of reference. The customer mistakenly believes that the function signal generator outputs a standard sine wave, which leads to such a wrong judgment. Later, a measured Agilent 100MHZ oscilloscope was used for testing, and it was found that the sine wave itself had burrs. In the end, the customer of course chose the 20MHz oscilloscope that measured the burrs. Therefore, it is very important to calibrate the oscilloscope used in the school every year.

2. Many colleges and universities have purchased a large number of low-end digital storage oscilloscopes in basic laboratories, but the experimental process does not require data storage, and such oscilloscopes are not as good as analog oscilloscopes in observing waveforms, which has caused a lot of unnecessary trouble.

3. For various reasons, many laboratories that have purchased high-end digital storage oscilloscopes have not fully utilized many advanced functions of the instruments, and they are only used as low-end digital storage oscilloscopes or even analog oscilloscopes, resulting in a serious waste of funds.

Several suggestions for choosing oscilloscopes in university laboratories

1. Choose an oscilloscope according to your actual needs.

The types, experimental contents, and instrument user levels of university laboratories are different. The choice should be made according to the specific conditions of each laboratory. Don't blindly think that high-end instruments are better than low-end instruments, and digital oscilloscopes are better than analog oscilloscopes. In many cases, for observing repetitive signals commonly seen in general teaching experiments, analog oscilloscopes are better than low-end digital oscilloscopes in terms of price and actual observation effect. For some professional laboratories with scientific research nature, it is very necessary to choose some high-end digital oscilloscopes.

2. Choose products from reputable and high-level manufacturers or agents.

At present, due to the expansion of colleges and universities, laboratory instruments are used very frequently. As a result, the reliability of the product and the timeliness of after-sales service have become important factors that university laboratories need to consider when choosing oscilloscopes. The same 20MHz oscilloscope has a price range from 1,000 yuan to more than 4,000 yuan, but it is obvious that the product quality and after-sales service enjoyed by users are completely different. When choosing an oscilloscope, you need to consider many aspects of price and service. Don't be impressed by the low price at the moment, otherwise it is likely to cause passivity in future work. (end)