Cirrus Research CR 151, Руководство пользователя

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optimus sound level meter user manual
Page 43
When the LED indicates the unit is switched on this produces the greatest radio
frequency emissions.
The calibrator continues to function after exposure to contact discharges up to 4kV
and air discharges up to 8kV, for both positive and negative voltages relative to earth
ground. The calibrator conforms to IEC 60942:2003 for a modulated root-mean-square
electromagnetic field strength of 10 V/m.
The maximum susceptibility to power and radio frequency fields is with the cavity
facing away from the emitter with the battery compartment facing the table, the
antenna polarisation horizontal and the calibrator switched on.
Free Field Correction
When calibrating a microphone which is to be used for free field measurements, a
small correction may be necessary to compensate for the difference between the
microphone’s free field response at ‘zero degrees’ or ‘head-on’ incidence and the
pressure level generated by the calibrator.
The correction is typically -0.3dB for ½ inch microphones (making the effective
calibration level 93.7dB).
Calibration corrections are listed below for the Cirrus Research plc ½” Capsules and
three microphone capsules commonly used in Calibration Laboratories:
Microphone Correction Values
Microphone Type Calibration Correction Effective Calibration Level
MK:202 -0.3dB 93.7 dB
MK:215 -0.3dB 93.7 dB
MK:226 -0.3dB 93.7 dB
MK:224 -0.3dB 93.7 dB
B&K 4134 0dB 94.0 dB
B&K 4180 0dB 94.0 dB
B&K 4192 0dB 94.0 dB
Example
An example of the procedure used to calculate the value for an MK:224 microphone is
shown below :
Level = 94.0dB + Microphone Correction
Level = 94.0dB + ( -0.3dB)
Level = 93.7dB