Determine the positive and negative poles of the speaker using a multimeter.
First, set the pointer multimeter to the DC 0~5mA range, and then connect the two test leads to the two solder tabs of the speaker to be tested. Press the paper cone of the speaker gently with your hand and observe the swing direction of the multimeter pointer. If the pointer deflects in the positive direction, the red test lead is connected to the negative electrode of the speaker and the black test lead is connected to the positive electrode of the speaker. On the contrary, the red test lead is connected to the positive pole, and the black test lead is connected to the negative pole.
Use a multimeter to determine the quality of piezoelectric ceramics
Piezoelectric ceramic is a synthetic piezoelectric material. When subjected to external pressure, charges will be generated on both sides, and the amount of charge is proportional to the pressure. This phenomenon is called the piezoelectric effect. Piezoelectric ceramics have a piezoelectric effect, that is, they will deform under the action of an external electric field, so piezoelectric ceramic sheets can be used as sound-generating components.
Using the piezoelectric effect of the piezoelectric ceramic piece, a multimeter can be used to judge its quality.
Lead two wires from the two poles of the piezoelectric ceramic piece, then place the ceramic piece flat on the table, connect the two leads to the two test leads of the multimeter, set the multimeter to the minimum current block, and then lightly press the ceramic piece with the pencil eraser. , if the multimeter pointer swings obviously, it means the ceramic piece is intact, otherwise, it means it is damaged.
How to use a multimeter to check for short circuit or grounding in a line
First, the live and neutral lines need to be separated.
Ground wire: Set the multimeter to the AC voltage range, and the range is higher than 220V. Insert the red test lead into the voltage hole, leave the black test lead unplugged, then insert the red test lead into one of the socket jacks and observe the reading.
If you want to check whether there is a short circuit in the line. First, power off the line, then open each load switch, and use the ohmmeter of a multimeter to check the resistance between the two wires. Normally, the larger the resistance, the better. If you want to determine whether the line is grounded, you can use the ohm block of the multimeter. To measure the resistance of each line to ground. The bigger the better. It should be pointed out that using a multimeter to measure whether a line is short-circuited or grounded is inaccurate. It shouldn't be. If the grounding or short-circuit resistance is very small, it can be detected with a multimeter. If the resistance is slightly larger, it can be detected. A multimeter cannot check it, as it is in a 380V low-voltage circuit. A 500V megger should be used for measurement, whether between lines or to ground. Both should be above 0.38 megohms. Otherwise it is unqualified.
If two readings are small and one reading is large, it means that the ground wire is not connected to the ground, and the ground wire is also connected to the neutral wire. There is no need to measure in the second step.
Turn the multimeter to the "short circuit" test function (if not, turn on the resistance test), connect the red and black test leads to the circuit ground and the mains ground respectively. If the test result is a short circuit, or the resistance is extremely small, the line is grounded. , and vice versa.
Check leakage and grounding, and set the multimeter to 200M. For example, when measuring the insulation of equipment, connect one end of the test lead to the equipment shell or ground wire, and the other end of the test lead to the line. When measuring insulation, do not touch the test leads with your hands to prevent measurement errors.
Adjust the resistance range of the multimeter to 20K or 200K, turn off the main power supply and load power, use a multimeter to connect one test lead to the live wire and one to the ground wire to check the resistance value, then connect one test lead to the neutral wire and one to the ground wire, watch For the two resistance values, if one appears to be above 7.3, or above 14., it means that the live wire or neutral wire connected to the resistance value is leaking.
