Sound level meter - Frequently Asked Questions

■ AC/DC output settings

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

【Note】

• Both the AC and DC output terminals have an output resistance of 50Ω ±2%, but they are not capable of driving a 50Ω termination resistor. Always connect a measuring instrument with an input impedance of 10kΩ or higher.
• The AC output signal contains an error (up to 15%). Therefore, always complete calibration with the connected equipment before use.

AC output

The AC output terminal outputs a signal with the following specifications, which has been frequency-corrected by analog processing.

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

±1V = 0.707Vrms = -3dBv

Here, if 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, when the measured level is -20dB below the upper limit of the level range display, the output signal is as follows (corresponding to 90dB when the level range is 40dB to 110dB).

0.707×10（-20）/20 = 70.7mVrms = -23dB

The internal calibration signal is -6dB above the upper limit of the level range display. Therefore, the voltage output from the AC output terminal will be 354mVrms or -9dBv (corresponding to 104dB when the level range is 40dB to 110dB). Also, when the AC output level is bVrms or adBv with a steady signal input, the indicated value on the display screen will be off by the following numerical value from the upper limit of the level range display.

20 × LOG10 (b/0.707) dB or a + 3 dB

For example, if the AC output is 100mVrms = -20dBv, the indicated value will be off by the following number of units from full scale.

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

In this case, a level range display of 40dB to 110dB corresponds to 93dB. 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 DC output terminal outputs a signal that corresponds to approximately the same level as the bar indicator, after being processed through a D/A converter (see specifications below).
The bar indicator has a 100ms update cycle, but the D/A converter output is updated approximately every 8.2ms. Therefore, it can respond to sudden level fluctuations.

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

2.5 + 0.5×a/10V

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

2.5 + 0.5×-20/10 = 1.5V

The internal calibration signal is -6dB above 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

Furthermore, when the DC output is in 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 the following number of units away from the upper limit of the level range display (equivalent to 93dB if the level range is 40dB to 110dB).

（1.65-2.5）/0.5×10 = -17dB

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