About audio level measurement
(1) The use of the multimeter dB block. There is a dB scale line on the dial of the multimeter, and it is written in the instruction manual to measure the audio level. Level is a parameter or quantity of electric power and voltage, and it needs to be expressed with relative values. dB is the letter symbol for decibels. The readings measured by the level shift indicate the value of the measured voltage or power after comparison with the marked value. According to internationally accepted regulations, use in the dB shift of a 600 O multimeter: add 1 mW of power, and the voltage value on the load. It is zero level. According to the formula, the AC voltage on the load at OdB is 0.775 V. At this time, the voltage on the multimeter and the decibel scale can correspond one by one. In other words, to measure the audio level is to measure the AC voltage. Therefore, when measuring the audio level, the changeover switch of the multimeter is actually set to the AC voltage block, but the test lead should be inserted into the “dB” jack because it is connected in series to the “dB” jack of the multimeter. A capacitor is used to isolate the DC component in the circuit under test.
(2) You can use a decibel scale or an AC voltage scale to measure the audio level.
There are several ranges of AC voltage, depending on the scale of the multimeter’s AC voltage of 10 V, the 0.775 V corresponding to OdB, because the decibel scale is calculated based on the AC voltage of 10 V. For example: 7. 75 V corresponds to 20 dB, and 0. 45 V corresponds to -10 <IB. It can be seen from the multimeter that the voltage reading and the decibel reading are not proportional. During the test, just look at the scale reading. It’s okay. Because the multimeter is defined by the concept of (level) that its size is proportional to the logarithmic value of the voltage or power ratio.
(3) The zero-level standard of the multimeter is 600. , 1 mW, or 500 Q, 6 mW, are marked on the dial of the multimeter. It can also be distinguished by the position of the zero decibel scale line of the multimeter. For multimeters with 600 (1, 1 mW as the zero-level standard), the zero-decibel scale is at 0. 775 V. For multimeters with 500 (1, 1 mW) as the zero-level standard, the zero-decibel scale is at 1.732 V.
The level value of the multimeter is marked with the AC 10 V gear as the reference scale. The level value at 10 V is +22dB. If the indicated value is greater than +22 dB, it can be set at more than 10 V and other AC voltage gears. Measure the level value, and the displayed value can be corrected by the correction value.
(1) When there is a DC component in the circuit under test, a 0.1 |xF DC blocking capacitor with similar withstand voltage can be connected in series to the “+” socket for measurement.
(2) The digital display multimeter is a resistance impedance type, which is slightly different from the mechanical moving coil multimeter (inductive impedance). It can be measured and used according to the above-mentioned principle according to its manual.
However, sometimes the measured load is not 600 £1, when the corresponding power is larger, the load is less than 600. When reading the decibel scale, an additional value should also be added as a correction. If the multimeter does not have a calibration table, you can check it in the electronic manual.
(3) Measure the signal with DC component.
The audio level is used to measure the gain of the amplifier stage and the loss in line transmission. When measuring audio, turn the knob to the 2.5 V gear, and then measure the audio output. If the amplitude is too small, turn the gear to mV to measure the amplitude of the audio level. Use a multimeter to measure the dB value, and use the lowest range of the multimeter’s AC block. When measuring a signal with a DC component, a large-capacity DC blocking capacitor should be connected in series.
Special note: For the measurement of standard audio level, a multimeter should be connected in series with a value greater than 0.1 |1F and greater than the measured voltage, such as a capacitance greater than 400 V and a standard impedance of 600. Measure -600 at both ends of the conveyor line. The voltage at both ends of the transmission line: 0 dB corresponds to 1 mW, 0. 775 V. When measuring the signal, if the meter is set to ACV 10 V, the number of dB read x 1, that is, the dB reading is the measurement result. On the meter head, the dB% of full gear is about 22 dB, which is the effective voltage of 10 V (AC voltage at full gear), and the number of dB generated by the internal resistance of 600 11: 10 x log (1 000×107600) = 22.2 (dB). The numerical correction values under different ranges are shown in Table 1.1.1. The measurement method is basically similar to that of AC voltage, turn the switch to the corresponding AC voltage block, and make the pointer have a larger deflection. If there is a DC voltage component in the circuit under test, a 0.1 |iF isolation capacitor can be connected in series in the “+” socket,