Nor1251 Class 1 calibrator NOT MANUFACTURED ANYMORE, REPLACED WITH NOR11255
The Class 1 Calibrators
The Nor1251 is a class 1 calibrator with an output level of 114dB @ 1kHz. The calibrator accepts full-inch cartridges right away and ½-inch cartridges by means of the included adaptor. An optional adaptor (the Nor1444) – available separately, permits the use of the calibrator with ¼-inch cartridges.
The sound calibrator working principles
Our selection of sound calibrators shares a common working principle. The difference between them lies solely in their accuracy.
|The microphone to be calibrated is placed in the coupler of the sound calibrator where the sound pressure level is generated by a miniature loudspeaker. The electrical signal — driving the loudspeaker — is generated by an electronic oscillator.
The sound pressure generated is measured with a pressure sensitive silicon sensor (patent pending). This signal is used to adjust the level of the oscillator signal.
The rear side of the silicon sensor is located in a separate, vented cavity to prevent pick-up of extraneous noise signals. Noise pick-up is further reduced by the use of a bandpass filter in the feedback path.
Because of the high stability of the silicon sensor and the electronic controller, the acoustic signal generated becomes virtually independent of the battery voltage and ambient conditions such as temperature, humidity and the atmospheric pressure.
The feedback principle automatically compensates for variation in the equivalent volume of the microphones. Hence, it creates an effective coupler volume many times the volume given by the mechanical dimensions of the coupler. The system even compensates for drift in the loudspeaker.
The acoustic coupler is vented to the inside of the sound calibrator, which in turn is vented to the outside for equalisation to the atmospheric pressure. A separate channel vents the rear side of the reference transducer to the outside of the sound calibrator.
A light emitting diode (LED) illuminates whenever the level control is in balance. When there is no microphone placed in the coupler, the loudspeaker will in general fail to generate and maintain the correct sound pressure in the coupler. This situation is indicated by a non-iluminated LED and the calibrator will switch off.
An electronic circuit inside the calibrator will switch off the power at approximately five minutes after the ON button was pressed. If a longer time period is required then the power button can be fixed in the ON position.