CR1625 battery.Measurement of resistance values of components or branches in circuits

　　When many of us electronic enthusiasts assemble and repair electronic devices, we often need to measure the resistance value of certain components or branches in the circuit. Beginners usually think that the measurement can only be accurate if the components are removed. In fact, in many cases it can be measured directly on the road, and there are many techniques for measuring the resistance of electronic components.

　　1. Roughly determine the resistance value of the component when it is open or short-circuited

　　When testing a circuit, if you suspect that a component is damaged (open circuit or breakdown short circuit), you can roughly measure its on-circuit resistance to make a judgment. For example: some diodes and transistors work in high current and high voltage situations and are more susceptible to damage. During maintenance, in order to make a quick judgment, you can use a multimeter to directly measure the forward and reverse resistance of the diode after the circuit is powered off. If the resistance values are both very large, it means that the circuit is open; if the resistance values are very small, it may be broken down. short circuit. At this time, you should also check whether there is a component with a small resistance connected in parallel with it. If there is, you need to solder one end of the diode before testing. Transistors can also be tested in the same way.

　　Some insurance and current-limiting resistors in the circuit generally have very small resistance values and are easily burned out and open circuited. When the circuit is powered off, these resistors can be directly detected on the circuit because they are usually connected in series between the load and the power supply. If the measured resistance value is less than or equal to

　　2. Be precise on the road

　　Measuring element resistance

　　The precise resistance of some components can be measured directly on the road. As shown in Figure 1, R1 and R2 have components with infinite DC resistance such as capacitors and switches that separate them from other parts of the circuit. After the power is turned off, measuring on the road is the same as taking it off. Although some components in the factory cannot be measured directly, their accurate resistance values can be measured indirectly. As shown in Figure 2, element 1 and element 2 are connected in series. If the resistance value R1 of element 1 is known, only the terminal voltages U1 and U2 of element 1 and element 2 need to be measured. According to the characteristics of the series circuit 11=12 and Ohm's law, it can be known that the terminal voltage of the component is proportional to its resistance value, so only by accurately measuring the values of Ul and U2, the resistance value of component 2 can be obtained (note: component 1 and Component 2 should all be linear components).

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