How to Choose the Appropriate Oscilloscope in University Laboratory
As a basic test instrument, oscilloscope was once a pet in college laboratory. At that time, twenty or thirty students in a laboratory gathered around an oscilloscope to listen to the teacher's explanation and test. With the substantial improvement of China's economic strength and the country's vigorous support for education, oscilloscopes have become an indispensable instrument for electronic laboratories in universities. Even in many vocational education colleges are equipped with many oscilloscopes of different grades. In the face of numerous oscilloscopes on the market, how to choose the right product according to the measurement needs of the laboratory has become an urgent problem faced by many universities.
â—† 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 major manufacturers of analog oscilloscopes are showing a decreasing trend. The United States has stopped producing analog oscilloscopes since the mid-1990s, and Japan has only 2-3 left. There are still about 10 in China.
At present, analog oscilloscopes are mainly used in laboratories, production lines, maintenance and some special field tests in colleges and universities.
Because the analog oscilloscope has more important brightness information in the three-dimensional display and has a refresh rate of hundreds of thousands of times at the same time, the analog oscilloscope has infinite resolution in time, that is, the analog oscilloscope measures the input signal continuously in time. Therefore, low-end digital oscilloscopes cannot completely replace analog oscilloscopes.
2. The current status of digital storage oscilloscopes: At present, the main manufacturers are American Agilent, Tektronix and LeCroy.
Taiwan's Guwei Company, as well as Beijing Puyuan Precision Electric Co., Ltd., which has sprung up in China.
Because digital oscilloscopes contain more technical indicators, many customers are still unable to find their reasonable needs among the many indicators.
â—† The main technical indicators of digital oscilloscope: bandwidth, sampling rate, storage depth and waveform update rate
Bandwidth: In order to ensure the accuracy of the test signal amplitude and rising edge, the bandwidth of the oscilloscope should be 3-5 times the frequency of the signal under test, and the accurate measurement should be 8-10 times or more.
Sampling rate and storage depth: Generally, the sampling rate given by the manufacturer is the maximum value, that is, the sampling rate reached at the fastest scan time. However, in actual measurement, the sampling rate is a variable indicator. As the scanning time becomes slower, the sampling rate also decreases accordingly. So its actual value depends on the time base and storage depth.
Sampling rate [MS / S] * [time / div × 10div] = memory depth
DSO samples the input signal, converts it to analog-to-digital, sends it to memory and performs related processing, and then displays it after digital-to-analog conversion. In addition, because the waveform update rate of a common digital oscilloscope is relatively low (about 100 times / second-10000 times / second), confusion will inevitably occur in actual tests. Therefore, when choosing a digital storage oscilloscope, not only the technical indicators but also the actual measurement of complex signals is more important.
Major digital storage oscilloscope manufacturers and product specifications
It is not difficult to see that in the digital storage oscilloscope industry, the three major US companies are far ahead in terms of technology and market share. However, the appearance of Puyuan Jingke makes the domestic oscilloscope industry rejuvenated after ten years 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 dedicate more wonderful products to us.
â—† The current situation of oscilloscopes in colleges and universities
At present, the use of oscilloscopes in colleges and universities is mainly concentrated in the physical experiment center, electrical and electronic experiment center and information professional laboratory.
The physics experiment center generally mainly uses a 20MHz dual-channel analog oscilloscope.
The electrical and electronic experiment center mainly includes analog circuit laboratory, digital circuit laboratory, electrical engineering laboratory, EDA laboratory, PLC laboratory. At present, the instruments used by various universities are not the same.
In general, the following problems exist in the use of oscilloscopes in college laboratories:
1. There is no standard calibrator. As an oscilloscope as a quantitative observation instrument, it is difficult for the laboratory to judge the accurate index of the oscilloscope. It is not enough to simply perform some simple tests with ordinary function sources. There was a customer who used a 6MHz function signal generator to output a 6MHz sine wave with an amplitude of 4mV, which was used to evaluate three different models of 20MHz oscilloscopes. Among them, one test result was found to have glitches on the sine wave. The waveform looks smoother when observed by two units. Therefore, customers believe that there is a problem with the oscilloscope with glitches, and it is good to have no glitches. In fact, this is a matter of reference. The customer mistakenly believes that the function signal generator outputs a standard sine wave, and this wrong judgment occurs. Later, a measured Agilent 100MHZ oscilloscope was used to test, and it was found that the sine wave itself had glitches. In the end, of course, the customer chose a 20MHz oscilloscope with glitches. Therefore, it is very important to calibrate the oscilloscope used in schools every year.
2. Many colleges and universities purchase a large number of low-end digital storage oscilloscopes in the basic laboratory, but the experimental process does not require data storage, and such oscilloscopes are not as good as analog oscilloscopes in observing waveforms, thus causing a lot of unnecessary trouble.
3. Many laboratories that purchase high-end digital storage oscilloscopes have not fully utilized many advanced functions of the instrument due to various reasons. They are only used as low-end digital storage oscilloscopes or even analog oscilloscopes, causing a serious waste of funds.
â—† Some suggestions on choosing oscilloscope in university laboratory
1. Choose an oscilloscope according to your actual needs.
The types of labs in universities and colleges, the content of experiments, and the level of instrument users vary. You should choose according to the specific circumstances of each laboratory. Do not blindly think that high-end instruments must be better than low-end instruments, and digital oscilloscopes must be better than analog oscilloscopes. In many cases, analog oscilloscopes outperform low-end digital oscilloscopes in terms of price and actual observation effects for the observation of repetitive signals common in general teaching experiments. For some professional laboratories with scientific research nature, it is very necessary to choose some high-end digital oscilloscopes.
2. Choose products from manufacturers or agents with good reputation and high level.
At present, due to the expansion of colleges and universities, the use of laboratory instruments is very frequent. In this way, the reliability of products and the timeliness of after-sales service have become an important factor that college laboratories need to consider when choosing an oscilloscope. The same is a 20MHz oscilloscope, the price ranges from 1,000 yuan to more than 4000 yuan, but it is obvious that the product quality and after-sales service that users enjoy are completely different. Choosing an oscilloscope needs to be considered in many aspects of price and service. Don't be impressed by the temporary low price, otherwise it may cause passive work in the future.
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