Digital multimeter resistance measurement methods and precautions
During measurement, the positive power supply charges the capacitor Cx under test through the standard resistor R0. At the moment when charging begins, since Vc = 0, "000" is displayed. As Vc gradually grows higher, the displayed value increases. When Vc=2VR, the instrument 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 period of time can be measured with a quartz watch. When using the 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.
How to measure resistance with digital multimeter
When measuring resistance, the reading should be read on the scale marked "ω" (since the current passing through the meter is not proportional to the resistance being measured, the resistance scale on the dial is uneven.) The resistance being measured The actual value of is equal to the reading on the scale multiplied by the multiple pointed by the knob. Before measuring, you should short-circuit the two test leads first, turn the zero-adjusting potentiometer so that the pointer is at 0ω, and then select the appropriate gear to ensure accurate measurement. Every time you change the limit, you need to reset the zero. In addition, the resistance measurement must be carried out passively and without other parallel branches. After the resistance (or current) measurement is completed, the transfer switch should be turned to the high voltage position. This is a good habit to prevent misuse of the ohmmeter (or current position) to measure voltage.
Precautions for digital multimeter resistance
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 "000" is constantly displayed, it indicates an internal short circuit in the capacitor; if overflow is constantly displayed, it may mean that the internal poles of the capacitor are open circuited, or the selected resistance level is inappropriate. When checking electrolytic capacitors, 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.
