Using standardized sound measurement instruments also requires standardized calibration.
It is important to choose a calibration laboratory that is certified to ISO/IEC17025 standards. But this is not all to look out for, the laboratory should also be accredited for the required methods and standards for the calibration of instruments.
ISO/IEC17025 has a wide range and it’s easy to get the licence but not so easy to get accredited in the correct methods / standards !
The main standard to use for calibration of sound measuring instruments Thailand is IEC61672-1. The calibration shall be performed according to IEC61672-3 method.
Some laboratories only use the simple (shortcut) calibration of sound level meters with a sound calibrator with 94dB / 114dB.
In the IEC61672-1 and IEC61672-3 methods (real calibration) there is a lot more testing needs to be included such as the acoustic signal test of frequency weighting and the electrical part of the instrument.
Important topics for calibration of sound measuring instruments that must be tested in the electrical sector according to IEC61672-3 standards are as follows.
– Self-generated noise
– Electrical signal test of frequency weightings
– Frequency and time weighting at 1 kHz
– Long-term stability
– Level linearity on the reference level range
– Level linearity including the level range control
– Tone burst response
– Peak C sound level
– Overload indication
– High-level stability
Calibration in ALT laboratory is carried out in accordance with IEC61672-3 standards, which includes calibration in both acoustics and electrical part.
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