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Hi there, I am trying to measure the current in a circuit by putting a digital ammeter inline, as in the diagram, after removing a connecting link that is also shown. When the connector link is in, the circuit works fine but when the meter is in it doesn't work well at all, implying that there is some significant resistance from the meter. In practice it looks like this: In the two photos, first I have have some jumper leads plugged in and the circuit runs normally. Plug in the meter instead and, while there is some current flowing, there is not enough for the system to function properly. As I understand it the ammeter should offer minimal resistance to the circuit and so should not interfere with it during it’s measurement process. Using another meter, when disconnected, the resistance of the red plug through to the black plug via the meter set to 'A' is 0.1 Ohms. I do have a clamp meter but I am expecting to use a desktop digital meter that will take readings automatically at regular intervals without my having to remember to stop and take one. Am I doing something wrong here and how can I obtain a good reading without interfering with the circuit's operation? Thanks
How is the current generated? The current is generated because of the positive and negative charges. The electrons are inside the metal conductor and actually flow from the negative electrode to the positive electrode. It can be imagined that there is a positive charge on the positive side of the power supply. Inside the metal conductor, the nucleus has little force on the electrons, and the electrons are easily separated from the nucleus. So the electrons in the metal conductor close to the positive electrode of the power source are first attracted by the positive charge of the positive electrode of the power source. In the past, the metal conductor that is close to the positive pole of the power supply loses electrons, and it becomes a positive charge itself. The free electrons of the metal conductor that follows it are attracted by this positive charge, and thus the current is formed. If the nucleus of a certain metal has a strong attraction to electrons, then the electrons move hard, which can be understood as "resistance is large". If the nucleus has a weak attraction to electrons, then the electrons move easily. Kind of situation can be understood as "small resistance" In fact, when the free electrons move in a direction, they will collide with the atoms on the crystal lattice. According to the classical conductivity theory of metal, the free electrons collide with the positive ions on the lattice, and the electron motion is hindered to generate resistance. The collision frequency is about 1015 times per second. In the microcosm, it is not advisable to understand with simple particles. In the atomic model, electrons outside the core are distributed according to certain rules. According to the principle of uncertainty, it is impossible to judge the position of the electron at the moment. Only the region where the electron is distributed has a probability distribution. The distribution map of the electron is called an electron cloud. The state of the electron can only be known through the electronic cloud. When an atom is excited by the outside world, the electrons will break away from the control of the nucleus and become free electrons. But the electrons will soon release the excited energy and then return to the electron cloud. Because the number of atoms in a conductor is a huge astronomical number, and the atom is in a state of being excited by heat, statistically, because the number of atoms in the conductor is huge, the number of free electrons is of course huge, so that the whole The conductor looks like a sponge filled with free electrons. From the perspective of energy, the electrons in the electron cloud are controlled by the nucleus, as if they are locked into a dense space. While the energy of free electrons is relatively high, it can move relatively freely. The energy relationship of the former can be called the forbidden band, and the latter is called the conduction band. The electrons move and return between the forbidden band and the conduction band. The function of the power supply is to establish an electric field that acts on the free electrons that satisfy the condition, causing it to move in an directional motion. Electrons are accompanied by excitation and return during motion, which is part of the resistance. Therefore, electrons can't actually be compared with ordinary physical particles. The two are actually different. Of course, you can understand it simply by particle model. The excitation of an atom involves the thermal motion of the atom, so the amount of free electrons is naturally closely related to the temperature of the material, as the resistivity increases with temperature. More articles about resistance and current, visit: Kynix semiconductor electronic blog