How to use the resistance range of a digital multimeter to detect capacitors
1.Measurement operation method
Set the digital multimeter to the appropriate resistance level, and the red test lead and the black test lead touch the two poles of the capacitor Cx under test respectively. At this time, the displayed value will gradually increase from "000" until the overflow symbol "1" is displayed. If it always displays "000", it means there is a short circuit inside the capacitor; if it always displays overflow, it may be that the internal electrodes of the capacitor are open circuit, or it may be that the selected resistance level is inappropriate. When checking the electrolytic capacitor, please note that the red test lead (positively charged) is connected to the positive electrode of the capacitor, and the black test lead is connected to the negative electrode of the capacitor.
2.Measurement principle
The measurement principle of measuring capacitors using resistance gears is shown in Figure 5-11(b). During measurement, the positive power supply charges the capacitor Cx under test through the standard resistor R0. At the moment when charging starts, "000" is displayed because Vc=0. As Vc gradually increases, the displayed value increases. When Vc=2VR, the meter starts to display the overflow symbol "1". The charging time t is the time required for the display value to change from "000" to overflow. This time interval can be measured with a quartz meter.
3. Measured data using DT830 digital multimeter to estimate capacitance
When using a DT830 digital multimeter to estimate the capacitance of a capacitor ranging from 0.1μF to several thousand microfarads, you can select the resistance range according to Table 5-1. The table gives the range of measurable capacitance and the corresponding charging time. The data listed in the table also have reference value for other models of digital multimeters.
The principle of selecting the resistance range is: when the capacitance is small, the high resistance range should be selected, and when the capacitance is large, the low resistance range should be selected. If you use the high-resistance setting to estimate a large-capacity capacitor, the charging process will be very slow and the measurement time will last a long time; if you use the low-resistance setting to check a small-capacity capacitor, the meter will always display overflow and you will not be able to see the change process because the charging time is extremely short. .
3. Use the voltage level to detect
Using a digital multimeter to detect capacitors at the DC voltage range is actually an indirect measurement method. This method can measure small-capacity capacitors from 220pF to 1μF, and can accurately measure the leakage current of the capacitor.
