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13 June 2024
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AMPETRONIC CMR3 Calibrated loop measuring receiver

Stock code
Model number
  • CMR3
AMPETRONIC CMR3 Calibrated loop measuring receiver
AMPETRONIC CMR3 Calibrated loop measuring receiver



A receiver designed for measuring the performance of audio frequency induction-loop systems in accordance with the requirements of the international defining standard EN 60118-4. The unit is battery powered, and offers a balanced line-level output which can be used with any suitable audio analyser or signal measuring system.

Built in a moulded grey case, the CMR3 has a power LED, a 3.5mm stereo jack socket for the active balanced output signal and a switch to set flat or weighted response. Power is turned on and off by inserting and removing the output cable connector.

Frequency response: +/- 0.25 dB, 50Hz to 8kHz, -3dB at 30Hz and 14kHz, with switched A-weighting filter according to EN61672-1:2003 sound level meters. Gain stability: Change due to battery voltage or output loading less than 0.1dB, temperature less than 0.25dB. Overall gain change less than 0.5dB. Output sensitivity: Calibrated to 0dBu output for 400 mA/m RMS magnetic field (as specified in EN 60118-4), headroom greater than 6dB before clipping. Load impedance 600 ohms minimum. Environment: -20 to +40°C. Power source: Two AA cells, alkaline types preferred, 200 hrs use approximately. Dimensions: 112 x 62 x 26 (l x h x d) mm. Weight: 84g.

Application note: The EN 60118-4 standard establishes the target field strength and frequency response of the induction loop system within the usable area. Tolerances are established for the various parameters. The standard also defines an acceptable level for the interfering background noise, which must be measured.
This receiver is intended to be used as a calibrated probe in conjunction with audio analysers and measuring equipment, including software-based audio analysers running on portable or fixed computers. When used with a suitable signal source and analyser, the magnetic field strength, background noise, frequency response and field distribution can be measured accurately. Loop system performance and losses due to the presence of metal in building construction can therefore be assessed, and the equipment can be set up to satisfy the requirements.

Included accessories: Output cable, 3.5mm stereo jack to XLR3-M, wired balanced, 1.5 metres.
Optional accessories: Two alkaline AA cells.
Warranty: Ampetronic offer a five year warranty on these items, effective from date of shipment, provided the equipment has been used exclusively for the intended purpose and has not been modified, altered, used in an inappropriate manner or repaired by a non-authorised person.