Using a digital multimeter to measure direct current
Digital multimeter Nowadays, digital measuring instruments have become mainstream and have the tendency to replace analogue instruments. Compared with analogue meters, digital meters have high sensitivity, high accuracy, clear display, strong overload capacity, easy to carry and simpler to use. The following VC9802 digital multimeter as an example, a brief introduction to its use and precautions.
(1)Usage a Before using, you should read the instruction manual carefully and be familiar with the role of power switch, range switch, jack and special socket. b Place the power switch in ON position. c Measurement of AC and DC voltages: according to the need, dial the range switch to the appropriate range of DCV (DC) or ACV (AC), insert the red pen into the V / Ω hole, insert the black pen into the COM hole and connect the pen in parallel with the line to be measured. Measurement of AC and DC current: Set the range switch to DCA (DC) or ACA (AC), insert the red pen into the mA hole (＜200mA) or 10A hole (＞200mA), insert the black pen into the COM hole, and connect the multimeter in series in the circuit to be measured. When measuring the direct flow, the digital multimeter can automatically display the polarity. e Resistance measurement: Set the range switch to the appropriate range of Ω, insert the red pen into the V/Ω hole and the black pen into the COM hole. If the measured resistance value exceeds the maximum value of the selected range, the multimeter will display "1", then a higher range should be selected. When measuring resistance, the red pen is positive and the black pen is negative, which is the opposite of the pointer multimeter. Therefore, when measuring transistors, electrolytic capacitors and other components with polarity, you must pay attention to the polarity of the pen.
(2). Precautions for use a If it is impossible to estimate the size of the measured voltage or current in advance, it should be dialled to the highest range stop to measure once, and then gradually reduce the range to a suitable position depending on the situation. When the measurement is finished, the range switch should be set to the highest voltage block and the power should be switched off.b When the meter is in full range, it only displays the number "1" in the highest digit and the other digits are disappeared, then a higher range should be selected.c When measuring voltage, the digital multimeter should be connected in parallel with the circuit to be measured. When measuring current, the digital multimeter should be connected in series with the circuit to be measured, and it is not necessary to consider the positive and negative polarity when measuring direct flow. d When the AC voltage block is mistakenly used to measure the DC voltage, or the DC voltage block is mistakenly used to measure the AC voltage, the display will show "000", or the number on the low position will appear to jump. e It is forbidden to use the digital multimeter in the measurement of high voltage (more than 220V) or large current (more than 0.5A), and it is also prohibited to use the digital multimeter in the measurement of high voltage (more than 0.5A). current (above 0.5A) to prevent arcing and burning of switch contacts. f When " ", "BATT" or "LOW BAT" is displayed, it means that the battery voltage is lower than the operating voltage.
