sound level meter Frequently Asked Questions

AC/DC output settings

The AC and DC output signals are output from the ANALOG OUT terminals. Devices such as level recorders and real-time analyzers can be connected to the AC and DC output terminals.

Notice

• Both the AC and DC output terminals have an output resistance of 50Ω ± 2%, but they do not have the capability to drive a 50Ω termination. Please connect measuring instruments with an input impedance of at least 10kΩ.
• The AC output signal contains an error (up to 15%). Therefore, please ensure that calibration with the connected device is completed before use.

AC output

The signal with the following specifications, which has undergone frequency correction through analog processing, is output from the AC output terminal.

Therefore, when a steady sinusoidal signal is input at the upper limit value of the level range display, the signal from the AC output terminal will be as follows.

±1V = 0.707Vrms = -3dBv

Here, when the input level of the steady-state sine wave signal is adB above the upper limit of the level range display, the signal from the AC output terminal will be as follows.

0.707×10a/20Vrms = -3 + adBv

For example, if the measurement level is -20dB compared to the upper limit of the level range display, the output signal is as follows (corresponding to 90dB in a level range of 40dB to 110dB).

0.707×10（-20）/20 = 70.7mVrms = -23dB

The internal calibration signal is -6dB below the maximum value of the level range display. Therefore, the voltage output from the AC output terminal will be 354mVrms or -9dBv (which corresponds to 104dB when the level range is 40dB to 110dB). Additionally, when a steady signal is input, if the AC output level is bVrms or adBv, the indicated value on the display screen will be separated from the maximum value of the level range display by the following numerical amount.

20×LOG10(b/0.707) dB or a + 3 dB

For example, if the AC output is 100mVrms = -20dBv, the indicated value will be a certain distance from the full scale.

20×LOG10（0.1Vrms/0.707）dB = -20dBv+3dB-17dB

At this time, the level range display corresponds to 93dB within the range of 40dB to 110dB. The maximum output level of the signal output from the AC output terminal is 0.707Vrms, and linearity is guaranteed up to this level.

■DC output

The signal from the DC output terminal is output after passing through the D/A converter, corresponding to a level almost the same as that of the bar indicator (see specifications below).
The update cycle of the bar indicator is 100ms, but the output of the D/A converter is updated at approximately an 8.2ms cycle. Therefore, it can respond to sudden level fluctuations.

Therefore, when a steady sine wave is input at the upper limit of the level range display, the DC output will be 2.5V. The scale factor is 0.5V/10dB. Thus, for levels above the upper limit of the level range display, the DC output can be expressed by the following formula.

2.5 + 0.5×a/10V

For example, if the upper limit of the level range display is -20 dB, the DC output level will be as follows (this corresponds to 90 dB when the level range is from 40 dB to 110 dB).

2.5 + 0.5×-20/10 = 1.5V

The internal calibration signal is -6dB below the upper limit of the level range display. Therefore, the DC output will be as follows (equivalent to 104 when the level range is 40dB to 110dB).

2.5 +0.5 × -6/10 = 2.2V

Also, if the DC output is bV, the indicated value on the display screen will be separated from the upper limit of the level range display by the following numerical value.

（b-2.5）/0.5×10dB

For example, if the output from the DC output terminal is 1.65V, the indicated value will be a certain distance away from the upper limit of the level range display (if the level range is from 40dB to 110dB, this corresponds to 93dB).

（1.65-2.5）/0.5×10 = -17dB

The maximum output level from the DC output terminal is 3V, which is the same as the level of a sine wave that indicates a value 10dB higher than the upper limit of the level range display. If a steady signal exceeds this level, 'OVER' will be displayed.