Portable Noise Monitoring Terminal (NMT) Type 3655-C-DMO is a complete solution delivered as part of Noise Sentinel – On Demand.

Noise Sentinel – On Demand enables you to monitor and manage noise through an end-to-end online experience: book and obtain instrumentation, collect and report data and maintain your data indefinitely in the cloud.


Portable NMT Type 3655-C-DMO comes complete with tripod, router, SIM card and airtime contract, antenna, sound level calibrator and all accessories required for deployment in the field. In addition, a smart phone App eases setup and configuration in the field, including easy location based on GPS, as well as entering location notes and photographs.

The NMT is delivered in two transport cases, one for deployment and one containing the accessories.

The NMT can operate off its own internal batteries for 32 hours (typical) with the router. In addition, it can operate off AC power or with external DC power.

Uses and Features


  • Measurements made:
    – Outdoors
    – Unattended
    – In workplaces and on construction sites
    – In remote locations
  • Measurements for:
    – Area planning
    – Noise control
    – Complaint investigation
    – Venue licensing


  • Weather protection to IP 43
  • Easy to carry and transport
  • Tamper protection
  • Includes all accessories needed for deployment and use – from analyzer to router with pre-paid SIM card to sound level calibrator
  • Hot swap of batteries
  • Type approved to IEC 61672 Class 1 specifications; uniquely, including windscreen effects
  • 120 dB dynamic range
  • Built-in facilities to minimise gaps in data
  • Charge Injection Calibration (CIC) for remote verification of the entire measurement chain
  • Safe and reliable live data streaming
  • 3G communication capabilities for remote operation
  • Industry-standard Internet and security protocols for safe and reliable data transfer

Inside the Case



Portable Noise Monitoring Terminal

The Portable Noise Monitoring Terminal Type 3655-C-DMO comes complete with tripod, router, SIM card and airtime contract, antenna and sound level calibrator and all accessories required for deployment in the field. The NMT is delivered in two transport cases, one for deployment and one containing the accessories.

Type 3655-C-DMO includes everything needed to take measurements:

  • NMT with microphone and cable
  • Tripod with guy ropes and pegs
  • 3G router, SIM card and airtime contract
  • Rechargeable 32 hr battery pack
  • Mains power supply
  • Cable for external batteries
  • Security cable and locks
  • Calibrator
  • Assembly toolkit
  • Shipping cases
  • Shipment to and from site
  • Assembly and testing instructions


The cases are light and robust, and their contents are secured in the case with high-density machined foam inlays. The cases are designed for unattended noise monitoring. They protect the measurement system from the weather and unauthorised access while providing power and remote data retrieval.


Type 3655-C-DMO comes with two powerful batteries and two chargers. Power for the system may be provided by any or all or the following:

  • One of the included batteries (QB-0079)
  • Both of the included batteries (QB-0079)
  • One of the included chargers (ZG-0857), provided mains power is available
  • Both of the included chargers (ZG -0857), provided mains power is available
  • External DC power 12 – 24 V

The internal batteries can power the system for 32 hours (typical) with the router. In addition, the hand-held analyzer has an internal Li-Ion battery, that provides a further 8 hours of power for the analyzer, itself.

The case’s batteries use lithium-ion (Li-Ion) technology, well known from mobile phones, portable PCs and hand tools. These lightweight batteries make Type 3655-C-DMO compact and completely portable. Li-Ion batteries are renowned for their excellent charge retention, lack of ‘memory’, and very high energy efficiency (5 times better power to weight ratio than traditional lead-acid batteries). For reliable long-life operation, the batteries have internal circuitry to protect against shorts and over-discharge.

The chargers are used to charge the batteries prior to measurements but may also be used to power the system during measurement if mains power is available. The NMT comes with a 1.5 m mains power cable for use with AC power (100 – 240 V AC, 0.6 A, 50 – 60 Hz).

You can also use an external 12 – 24 V DC power source that includes a suitable power guard to enable correct and safe restart after external power has been lost.

All power sources are connected to the case’s power panel, which always directs power from the source with the highest voltage to supply the measurement system and optional modems.

You may connect or disconnect power sources at any time during measurement as long as just one power source remains in operation, including during hot-swapping of batteries.

Reliable Unattended Measurements

Measurement integrity is of primary importance in noise measurement situations, whether for inside or outside or for attended or unattended measurements. Class 1, as described in the current sound level meter standard IEC 61672 – 1:2002, is the grade of accuracy often required for hand held measurements.

In addition nothing less than Class 1 accuracy is required for outdoor measurement systems incorporating rain shields, wind shields or any other form of environmental protection used in microphone systems. Placing a small device, such as a rain guard, in close proximity to the microphone diaphragm may produce significant acoustic disturbance and thus measurement errors at mid and high frequencies.

Hand-held Analyzer Type 2250-L and Outdoor Microphone Type 4952 are a type approved system combination, independently approved to Class 1 accuracy by PTB in Germany (see type approval certificate: Fig. 2). This ensures that the measurement system complies with the minimum requirements of accuracy for unattended noise measurement, a consideration often overlooked in portable noise measurement systems. Type approval of the system to IEC 61672–1:2002 also permits the weather-protected measurement system to be laboratory calibrated in accordance with part III of this sound level meter standard.


 Outdoor Microphone Type 4952

The compact and lightweight Outdoor Microphone Type 4952 is suitable for long periods of unattended outdoor operation and the ideal choice for use with the Type 3655-C-DMO system.

The microphone is protected against the effects of wind, rain and perching birds and, with the hand-held analyzer, fulfils IEC 61672 Class 1 requirements. The reference direction angle of incidence can be set to 0° or 90°, dependent on the noise monitoring application. Inside the microphone is a highly stable pre-polarized free-field 1/2" microphone cartridge with a stainless steel diaphragm.

You can mount the microphone on the supplied tripod using Tripod Adaptor UA-1707 or on a 1" thread pole.

Type 4952 is recommended for extended use in all kinds of weather. Up to 100 m of microphone extension cable can be used while maintaining measurement accuracy.

Based on Hand-held Analyzer Type 2250-L with Noise Monitoring Software BZ-7232, it functions exactly as Noise Monitoring Terminal Type 3639-A in a portable case rather than a mounted cabinet.

The noise monitoring functionality includes CIC checks, optional event detection and sound recording for extended periods of monitoring. The unit includes a router for remote viewing of real-time results and to remotely control the unit from Noise Sentinel – On Demand. Data can be automatically downloaded realtime or on connection with the server.

We help our customers measure and manage the quality of sound and vibration in their products and in the environment
Brüel & Kjær Sound & Vibration Measurement A/S. P +45 77 41 20 00. F +45 45 80 14 05. info@bksv.com
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