I was also an "enthusiast" in the 1970s, when I was called a "radio enthusiast". Why should I make a multimeter? As a result of studying in the Chinese University of Science and Technology for some time, in the mid-1970s, enthusiasts at that time usually assembled red light 7 1 1, OTL or OCL power amplifiers, superheterodyne transistor radios and black-and-white kinescope televisions, and so on, and there were fewer multimeters made by themselves. Because of the need of design, there were often fewer design materials at that time, fewer books in China, fewer people who could understand foreign materials, and even fewer translation materials, and they needed theoretical knowledge to calculate, so they had self-control things.
Back in February, 1974, I didn't put it down after graduating from high school. After hiding for two months, I went to work in the repair department of a radio console under Hefei Electronic Bureau to repair TV sets.
One day, Wu Zongzhi, director of the repair department, called me to his office and told me that China University of Science and Technology was going to give students a course on the principle and maintenance of TV sets. "I think it is more appropriate for you to go. You have installed several TV sets and have maintenance experience. Please get ready. If you don't repair TV at work, you are allowed to recite classes. "
At that time, the repair department had four repair groups: TV, amplifier, radio, instrument and instrument group. I was in the ***3-person TV group. The group leader is the biggest student who graduated before the Cultural Revolution. His surname is Yan, so we call him Master Yan. The other is the newly allocated college students of workers, peasants and soldiers. After decentralization, I went to school as Master Ge. I graduated from high school and love broadcasting. With the consent of director Wu, I entered the repair department and studied repair with Master Yan. At that time, because there was no work permit (if people without work permit were arranged, they might really be labeled as destroying going to the countryside), the personnel department did not agree to establish labor relations to pay wages. Later, I got a work permit and became an informal "contract worker". Later, this kind of length of service was recognized and counted as length of service, because "de facto labor relations" have been formed in law.
I didn't experience a lecture, but I wasn't afraid at that time. The more wit, the less courage. It was this lecture that I met Mr. Xue Dianan from the Basic Department of the Chinese University of Science and Technology. At that time, he was the counselor of this class of workers, peasants and soldiers. He agreed to give them five classes. I followed this class for more than a year and listened to the courses of transistor circuits and electronic circuits, which made me systematically learn some circuit design knowledge, and then laid the foundation for later making a multimeter, and successfully designed and manufactured it.
Later, Mr. Guo was transferred to the Beijing Graduate School of China University of Science and Technology, and retired as the party secretary of the school.
Learning how to design a multimeter will help us to improve our circuit analysis ability, deepen our understanding of the working principle of the multimeter and improve our hands-on ability.
After the resumption of the college entrance examination, there is a big electrical problem (physics and chemistry) in the exam questions of 1978, which is a comprehensive problem of telephone and series-parallel circuit calculation of multimeter. Very practical. Based on the complex calculation of series-parallel circuit, many fresh graduates are caught in this problem. After I got the question, I finished it faster. I really want to thank you for this period of study in China University of Science and Technology. Later, I left the repair department and recruited into Hefei Pharmaceutical Factory. I also asked Mr. Xue to help me with the related courses of high-frequency circuits in the radio department, which benefited a lot.
I made a multimeter with an internal resistance of 2600 ohms and 38 microamperes. The manufacturing range is: DC current is 5 mA, 50 mA and 500 ma respectively; DC voltmeter with DC voltages of 5 volts, 50 volts and 500 volts respectively; The AC voltage is conveniently 50 volts and 500 volts; The resistances are 10 ohm, 100 ohm, 10 ohm and 10 ohm. The watch case itself is made of wood and is still preserved today. Now I'm stuck in Melbourne because of the epidemic, so I can't take pictures.
Now, more than 40 years have passed, and the made pointer multimeter has become a thing of the past (antique). Now people use the new digital multimeter, which is characterized by high precision, strong resolution, perfect test function, fast measurement speed, intuitive display, strong filtering ability, low power consumption and easy to carry. Since 1990s, digital multimeter has become a necessary instrument for modern electronic measurement and maintenance, and is gradually replacing the traditional analog multimeter. But I still like to use pointer multimeter. I always have a nostalgic feeling and lingering memory.
Photo 1, pointer multimeter; Figure 2. Digital multimeter.