Things to do before using your multimeter
1) Calibration of the digital multimeter: the display shows 0.0Ω, indicating that the digital multimeter is normal.
2) Check the power connection: whether the connection of the experiment box is intact and whether the power supply is normal. The physical circuit, analyze the function realized by the circuit; operate the corresponding switch of the experiment box, observe the fault phenomenon, analyze the cause of the fault and diagnose and eliminate the fault, and fill in the fault diagnosis process record form (Table 4).
3) Detect the point of failure. Through the analysis of the cause of the fault, the students are guided to formulate a fault diagnosis plan. While sorting out the diagnosis plan, let the students master the troubleshooting process. Before the measurement, the teacher explained the basic troubleshooting principles: first simple and then complex, first easy and then difficult, first components and then wires. Assist students to measure according to their own diagnostic scheme. In the fault finding process, the "resistance method" is used to judge the fault range, and the "potential method" is used to confirm the fault point.
4) Confirm the fault. According to the measurement results, judge whether the electrical devices are normal, whether the auxiliary devices and connecting wires are normal. When measuring components with the electrical barrier of a digital multimeter, displaying "1.0" means that the components are open, and if it displays "0.0", it means that the components are short-circuited. In the same way, when measuring auxiliary components such as switches and relays, the resistance is also observed to confirm the fault.
5) Troubleshooting. Confirm the fault point and judge the fault type. After confirming the fault, raise your hand to signal, and after confirmation by the examiner, troubleshoot and verify. If there are multiple faults in the circuit, students need to arrange them one by one. 3) Emphasize the precautions: the digital multimeter is connected to the test leads correctly, the correct gear range is selected, and the safe use of the external 220 V AC power supply of the test bench is emphasized.
