Digital multimeter resistance measurement method and precautions
During measurement, the positive power supply charges the measured capacitor Cx through the standard resistor R0. At the beginning of charging, due to Vc=0, it displays "000". As Vc gradually increases in height, the displayed value also increases. When Vc=2VR, the instrument displays the overflow symbol "1" at the beginning. The charging time t is the time required for the displayed value to change from "000" to overflow, and the distance during this period can be measured using a quartz meter. When using the DT830 digital multimeter to estimate the capacitance of capacitors ranging from 0.1 μ F to several thousand microfarads, the resistance range can be selected according to Table 5-1, which provides the range of measurable capacitance and corresponding charging time.
Measurement method for resistance of digital multimeter
When measuring resistance, the reading should be viewed on the scale marked with "ω" (because the current passing through the meter is not proportional to the measured resistance, the resistance scale on the dial is uneven.) The actual value of the measured resistance is equal to the reading on the scale multiplied by the multiple indicated by the knob. Before measurement, the two probes should be short circuited, the zero potentiometer should be turned to make the pointer at the 0 ω position, and then the appropriate gear should be selected to ensure accurate measurement. Every time the limit is changed, it needs to be reset to zero. In addition, the measurement of resistance must be carried out in a passive and non parallel manner. After measuring the resistance (or current), the conversion switch should be turned to the high voltage position. This is a good habit to prevent the misuse of the ohmmeter (or current position) to measure voltage.
Precautions for resistance of digital multimeter
Set the digital multimeter to the appropriate resistance range, and distinguish between the red and black probes that touch the two poles of the tested capacitor Cx. At this point, the displayed value will gradually increase from "000" until the overflow symbol "1" is displayed. If "000" is continuously displayed, it indicates an internal short circuit in the capacitor; If overflow is continuously displayed, it can cause an open circuit between the internal poles of the capacitor, or it can cause the selected resistance range to be inappropriate. When inspecting electrolytic capacitors, it is important to note that the red probe (positively charged) should be connected to the positive terminal of the capacitor, and the black probe should be connected to the negative terminal of the capacitor.
