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Application Example
Measurement Quantities
In this application example, the CoCo will measure following quantities in a typical construction site:
1. Tonal noise: Noise containing a prominent frequency and characterized by a definite pitch.
2. CNEL: Community Noise Equivalent Level.
3. Hourly energy mean noise levels (Leq): See definition in Sample Noise and Vibration Control and Monitoring Plan attached to this Section.
4. Maximum Noise Level (Lmax): See definition in Sample Noise and Vibration Control and Monitoring Plan attached to this Section.
5. Peak Particle Velocity (PPV): Peak Particle Velocity.
Measurement Description
Following picture shows the data processing diagram for ONE input channel of CoCo for all the sound level meter measurements when A-weight is applied.
Sound level meter computation diagram.
In the sound level meter measurement, after the digitized data comes in, it is split into three paths: one goes to frequency weighting A, B, C or Z and one goes to C weighting or no weighting. The peak detection is computed from the output of C weighting or no weighting. The output of frequency weighting (A, B, C or Z) is further split into two paths. The first will go to a time weighting function which is more or less equivalent to an exponential averaging mode to calculate LAF; the second path goes to a time averaging function, which is equivalent to a linear averaging mode to calculate Leq.
The general measurement block diagram can be described in the following picture:
A CoCo with four channel IEPE inputs will be used for each monitoring device.
Ch1 will be connected with an outdoor microphone. The signal will be digitized and applied with A frequency weighting. This weighting function is implemented in the time domain. Then two signals will be computed. An Leq that uses 15 min averaging and an Lmax using slow time weighting.
In this project we use the outdoor microphone that manufactured by G.R.A.S. as shown below.
Ch2, 3 and 4 will be connected to the X, Y and Z ends of a tri-axis accelerometer. The three vibration signals will be summed in vector and create the fifth channel. PPV will be applied to ch 2, 3, 4 and 5 (summed channel). Lmax over 1 min will be calculated. The actual peak detection rate will be much faster. A tri-axis accelerometer from PCB Piezotronics is used.
For this particular project the unit will only be active on certain days in a week. On every day the measurement time will be 7am to 5 pm, Mon-Friday. For general applications, the monitoring can be continuous and 24/7.
The picture below shows a screen capture of the EDM PC host software. It displays the input channel status of the CoCo hundred miles away.
When one or more signals exceed certain predefined limits, the email can be automatically sent to an email address.
Alarm limits are set to each of the signals being monitored. When a signal exceeds the alarm, an email will be automatically sent to a designated email address. The email will contain following information:Signal name, time that alarm was triggered and the data value of the signal when trigger happened.
The measurement signals can be shown remotely in two ways:
a). In the PC EDM software where the operator controls and,
b). On the website.
The website will only show limited signal values.
The chart below is the live update display shown on the website that remotely monitors the CoCo inputs.
For this particular application about construction noise monitoring, viewing the measurement value live on the website is good tool for the resident community to see the actual noise levels happening in the field.
From time to time, the user can then download the signals files from CoCo to PC. This can be achieved by executing a special command on the EDM. A easy to use user interface is developed based on EDM platform. The user can operate the CoCo unit remotely through the control panel.
While the speed of data transfer is always a limitation, CoCo functions are very flexible to deal with various sophisticated tasks.
