Some precautions in the measurement of multimeter
Notes on resistance measurement:
(1) If the measured resistance value exceeds the maximum value of the selected range, it will display over-range "1", and a higher range should be selected. For resistances greater than 1 MΩ or higher, it will take a few seconds for the reading to stabilize. This is normal for high resistance readings;
(2) When there is no input, such as an open circuit, it will display "1";
(3) When checking the internal circuit impedance, ensure that all power supplies of the tested circuit are powered off and all capacitors are discharged;
(4) When 200MΩ is short-circuited, there are about four characters, which should be subtracted from the reading when measuring. For example, when measuring l00MΩ resistance, it will be displayed as 101.0, and the fourth character should be subtracted;
(5) The quality of the capacitor can be roughly detected by the resistance file. Connect the positive electrode of the capacitor with the red test lead, and the negative electrode of the capacitor with the black test lead. The reference power supply of the multimeter will charge the capacitor through the reference resistance. Normally, the charging voltage displayed by the multimeter will change from a low value. Start increasing gradually until overflow is displayed. If the overflow "1" is displayed at the beginning of charging, it means that the capacitor is open circuited, and if it is always displayed as a fixed resistance or "000", it means that the capacitor is leaking or short circuited;
(6) When checking the continuity of the circuit, as long as no beep is heard during the measurement, it can be judged that the circuit is unconnected;
(7) When measuring a resistance with a small resistance value, the two test leads should be short-circuited first, and the self-resistance (generally 0.2 to 0.3 ohms) of the connection line of the test leads should be read to correct the measured resistance value;
(8) The resistance gear has an overvoltage protection function, and the instantaneous mismeasurement of the voltage within the specified range will not cause damage. For example, the maximum allowable input voltage (DC or AC peak value) of the DT-830 digital multimeter resistance file is 250 volts, which is the safe value of the instrument when the resistance file is misused to measure voltage, but it cannot be charged (such as batteries, human bodies, etc.) Measuring resistance, this will cause the accuracy of the multimeter resistance to decrease, or even damage it.
The use and precautions of hFE files
This gear is mainly used to measure the β value of the magnification of the triode. Before measuring, it must be determined whether the triode is PNP or NPN, and the polarity of each pin must be confirmed.
(1) Other precautions for using the multimeter:
(1) In the process of using the multimeter, do not touch the metal part of the test lead with your hands, so that on the one hand, the accuracy of the measurement can be guaranteed, and on the other hand, personal safety can also be guaranteed.
(2) When measuring a certain amount of electricity, it is not possible to change gears while measuring, especially when measuring high voltage or large current, more attention should be paid. Otherwise, the multimeter will be destroyed. If you need to shift gears, you should disconnect the test leads first, and then measure after shifting gears.
(2) Precautions for digital multimeter maintenance:
The digital multimeter is a precision electronic instrument, do not change the circuit at will, and pay attention to the following points:
① Do not use beyond the range;
② Please do not use the multimeter when the battery is not installed or the back cover is not tightened;
③The battery and fuse can only be replaced after the test lead is removed from the multimeter and the power supply is cut off. Battery replacement: Pay attention to the use of the 9V battery. If you need to replace the battery, open the back cover screw and replace it with the same type of battery. When replacing the fuse, please use the same type of fuse;
④ After using the multimeter, the transfer switch should be placed in the "OFF" position. If it is not used for a long time, the battery inside the multimeter should also be taken out to prevent the battery from corroding other components in the meter.
