6
The NMT can be powered from a variety of sources, such as solar panels connected through the DC supply
input. An external UPS can be connected through the DC supply input.
The cabinet also includes a mains outlet and cable for peripheral equipment that can be powered from the
NMT. For example, a laptop can be powered from the NMT for setting up the NMT locally.
A 10 m microphone cable is included to ensure that the outdoor microphone and the cabinet can both be
positioned in the correct acoustical location, while being conveniently and securely mounted.
Due to the clever design of the NMT, it is easy to add new accessories, for example, a GPS unit, even after
the installation of the NMT on a wall or a pole.
Noise Monitoring and Analysis
Noise monitoring and analysis is performed by Noise Level Analyzer Type 4441 and System Controller
UL-0235. The Noise Level Analyzer measures data coming from the outdoor microphone and this data is
logged onto the System Controller.
The NMT can be calibrated using Sound Calibrator Type 4231. In addition, the system has built-in CIC
allowing automatic routine electrical checks to detect changes and faults in the system. CIC is a patented
technique used for remotely monitoring the entire measurement setup including the microphone,
preamplifier and connecting cable. The NMT can initiate up to four automatic, routine system checks per
day at user-specified times, storing results for later download and investigation.
A built-in display showing the primary measurement parameters and setup information is included for
servicing and type approval, it is only activated when the NMT cabinet door is open, reducing power
consumption.
The NMT complies with IEC 61672 Class 1 specifications and has a dynamic range of 110 dB.
Broadband Measurements and Frequency Analysis
The NMT performs all the broadband analyses needed for environmental noise measurements, measuring
L
eq
, L
peak
, L
im
, L
inst
, L
max
, and L
min
. All values can be calculated for different time and frequency weightings
(see specifications).
The NMT performs octave or 1/3-octave analyses at filter centre frequencies from 12.5 Hz to 20 kHz. It
can also identify noise events, for example, to restrict the duration of frequency analysis to reduce
memory usage, and monitor L
Aeq
-based statistics (for Type 3639-E-200 series configurations; this requires
a license for Event Analysis Software BZ-7844).
Storage of Results in a Database
The NMT stores data in a database on the System Controller. The standard capacity of the database is
40 GB, corresponding to an average of six months of storage time (depending on the remote control
software used). The retention period can be set up for all data sets.
The following parameters are stored:
• Hourly reports – Statistical information for every whole hour including Total L
eq
, Distribution
• Short reports – User-defined short reports for a period of 1 to 60 minutes calculating minimum values,
maximum values, L
eq
and five user-defined L
N
values
• Calibration reports – Automatically checks the calibration of the system four times a day using the patented
CIC check and stores the information in the database
The following is also stored (for Type 3639-E-200 series configurations, Event Analysis Software BZ-7844 is
required):
• Hourly reports – Extended to include Total L
eq
, Background L
eq
, Noise Event L
eq
• Noise events – Detects noise events from any user-defined trigger level and duration, and stores the
information in a database. Event trigger level and duration settings can be set on an hourly basis, enabling
