Noise is a very complex and fluctuating phenomenon mainly caused by human activities and therefore not following a natural course, with other words taking a sample now and then does not say much about this phenomenon and you need to sample continuously. Sampling continuously produces an impractical amount of data, luckily our data loggers are provisioned with aggregation channels that can help to reduce it to manageable proportions.
Type of microphone or noise sensor for proper monitoring
To monitor noise you need a microphone that can measure and analyze sound pressure and that outputs a signal corrected against the sensitivity curve of human hearing (A-weighting), such signals are referred to as LA (A-weighted, sound level) and are expressed in dB(A).
An example of such a microphone/noise sensor is the Rika RK300-06-BA with MODBUS/RTU interface.
Commonly monitored noise parameters
Commonly monitored noise parameters are:
- LAeq (A-weighted, equivalent sound level): This value can be acquired by averaging the sampled sound levels, but as dBA is a logarithmic value it can’t be averaged like a linear scalar value, you need to specify that the input type of the aggregation is a value expressed in dB.
- LA95 (Background noise): Background noise is often defined as the noise level exceeded for 95% of the measurement period. The data logger is capable to determine up to 3 different percentiles per channel, where sampled values are arranged by magnitude in ascending or descending order. To acquire the LA95 background noise you have to specify a 95% percentile arranged in descending order using LA as input value.
- LA10 (Peak load noise): The peak load noise is often defined as the noise level exceeded for 10% of the measurement period. To acquire the LA10 peak load noise you have to specify a 10% percentile arranged in descending order.
Aggregation channel 1
 Input parameter >> LA (Noise) (LA)
 Input type >> dB
 Aggregation period >> 00:10:00
 Average >> LAeq (Average)
 Minimum >> LAmin (Minimum)
 Maximum >> LAmax (Maximum)
 Gust >> Not used
 Deviation >> Not used
 Percentile 1 >> LA95 (Background) (95% descending)
[A] Percentile 2 >> LA10 (Peak Load) (10% descending)
[B] Percentile 3 >> Not used
Final additional notes
- The buffer of an aggregation channel is limited to 600 values, if your aggregation requires more values it will be reduced to 600 by using intermediate averages.
- A noise microphone can’t be powered from the 12V excitation switch of a logger, as such a microphone requires continuous power. When using an ML-417DS-SLA you can connect the noise sensor to the 12V (battery) output of the power PCB, else you can power the sensor from an ML-OP-524 option board set to supply a constant 12V.