Detailed Operating Steps for Voltage Measurement with a Multimeter
① Turn the multimeter selector switch to the proper range. Identify whether the voltage to be measured is DC or AC, and switch to the corresponding voltage range (DC voltage range or AC voltage range). If the polarity of the voltage is unknown, start with the maximum DC voltage range for a trial measurement. If the pointer deflects, the voltage is DC. If the pointer remains stationary (this may happen due to excessive range or AC voltage), switch to the maximum AC voltage range for another trial. If the pointer deflects, the voltage is AC. If the pointer still does not move, switch down to the next lower DC voltage range and test again. If the pointer moves, it is DC voltage; if not, proceed to the next lower AC voltage range, and so on.
② Select a suitable range. Estimate the approximate value of the DC voltage according to the power supply in the circuit under test to select the range. If the voltage magnitude is unknown, perform a trial measurement on the highest voltage range first, then gradually switch to lower ranges until a proper range is found. The criterion for a suitable voltage range: the pointer should deflect to more than two‑thirds of the full‑scale reading on the dial. (Note that this differs from the multiplier selection rule for resistance ranges.)
③ Measurement method. When measuring voltage with a multimeter, connect the multimeter in parallel with the circuit under test. Connect the red probe to the high‑potential point of the circuit (the DC current inflow terminal), and the black probe to the low‑potential point (the DC current outflow terminal). For example, when measuring the voltage of a dry cell, connect the red probe to the positive terminal of the dry cell and the black probe to its negative terminal.
④ Correct reading:
(1) Locate the voltage scale: Examine the dial carefully. The DC voltage scale is the top scale line on the meter. The symbol "V" below the top scale line indicates that this scale can be used for reading AC/DC voltage and current.
(2) Select the proper scale. Below the top scale line are three separate scales: 0‑50‑100‑150‑200‑250, 0‑10‑20‑30‑40‑50, and 0‑2‑4‑6‑8‑10.
(3) Determine the minimum scale division: Identify the minimum scale unit based on the selected scale. For example, on the 0‑50‑100‑150‑200‑250 scale, each small division represents 5 units; on the 0‑10‑20‑30‑40‑50 scale, each small division represents 1 unit; on the 0‑2‑4‑6‑8‑10 scale, each small division represents 0.2 units.
(4) Read the pointer indication value: Read the value according to the pointer position and the selected scale. For example, if the pointer is two small divisions to the right of 100 on the 0‑50‑100‑150‑200‑250 scale, the reading is 110.
(5) Calculate the measured voltage value: Obtain the actual voltage from the pointer reading and the selected range. For example, if the selected range is 2.5 V and the reading is 110 (read from the 0‑50‑100‑150‑200‑250 scale), the measured voltage is calculated as: (110/250) × 2.5 = 1.1 V
(6) Keep your line of sight perpendicular to the pointer when taking readings. That is, read the value when only the physical pointer is visible and its reflection in the curved mirror cannot be seen.
