About the method of measuring the internal resistance of lithium battery with multimeter
1. Electricity measurement: Electricity measurement is mainly to measure the quality of its charge and discharge, adjust to the ohm gear, and then use two test leads to connect its two feet respectively. At this time, the number on the meter will gradually increase, and finally become Infinity, and then change the pen, the situation is the same as before.
2. Measuring resistance: Measuring resistance is mainly to measure whether its resistance value is accurate, adjust it to the ohm gear, connect its two feet with a test pen, and see if the reading of the multimeter is the same as the actual resistance value of the resistance.
3. Measuring inductance coil: The main purpose of measuring inductance coil is to test whether it is conducting or not, and it is also in the ohm range. Just connect its two legs with a test pen. The inductance is simply a wire, and its resistance value should be very small.
4. Measuring transformer: There are many similarities between measuring transformer and measuring inductance.
Measuring principle of multimeter AC voltage range
VD1 and VD2 in the circuit are rectifier diodes in the meter, because the meter can only flow DC current, so when measuring AC voltage, the AC current must be converted into DC current, which is completed by a rectifier circuit composed of two diodes, C1 is The DC blocking capacitor in the meter prevents the DC current in the external circuit from flowing through the meter to prevent the DC current in the external circuit from affecting the measurement results of the AC voltage. Us is the AC voltage in the external circuit to be measured.
Multimeter AC voltage range measurement principle circuit diagram
The AC voltage in the external circuit is added to the rectifier circuit through C1, and the AC current (the AC current generated by the AC voltage) is converted into a DC current. This DC current meter deflects the pointer, which is only the AC voltage value.
Regarding the principle of AC voltage block measurement, the following points should also be explained.
1. When measuring AC voltage, connect the red and black gauge sticks in parallel to the voltage source to be measured in the external circuit, which is very convenient to operate.
2. Although the AC voltage is measured, the rectifier circuit in the meter will flow through the meter head with a DC current.
3. When measuring the AC voltage, the battery in the meter does not supply power, and the current that deflects the pointer is provided by the AC voltage source in the circuit under test. Since the drop-down resistor in the meter is very large (not shown in the figure), the measurement is The influence of the measured voltage source is also very small.
4. When there is no voltage in the circuit under test, there is no current flowing in the meter head, the pointer cannot deflect, and the voltage indication is zero. In the same range, the greater the voltage in the external circuit, the greater the rectified DC current flowing through the meter head, the greater the deflection angle of the pointer, and the greater the indicated voltage value.
5. Since the battery in the meter is not used when measuring the AC voltage, the voltage of the battery in the meter does not affect the measurement of the AC voltage.
6. When measuring AC voltage, there must be a power supply in the external circuit, so the external circuit should also be energized when measuring.
7. Since the direction of the AC current is constantly changing, and the AC voltage block of the pointer multimeter is only used to measure the 50Hz AC, the positive and negative half-cycle amplitudes of this AC are symmetrical, so the AC voltage sent into the meter must pass through the rectifier circuit. The direction of the current flowing through the meter head is determined. In this way, when measuring AC voltage, the red and black gauge sticks have no polarity and can be used interchangeably, which is not like measuring DC voltage or DC current.
8. The AC voltage block indicator dial of the pointer multimeter is designed for 50Hz sine wave AC, so when measuring non-50Hz sine wave voltage or other frequency ^ sinusoidal voltage, the measured voltage is not accurate, they can use digital Multimeter measurement.
9. The AC voltage indication scale is based on the effective value of the sine wave voltage.
