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Calibration of measurement systems.
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Regulations current to Apr 12, 2013
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 All Regulations
Part 325
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Subpart C - Instrumentation
Code of Federal Regulationsยง 325.25Calibration of measurement systems. (a)(1) The sound level measurement system must be calibrated and appropriately adjusted at one or more frequencies in the range from 250 to 1,000 Hz at the beginning of each series of measurements and at intervals of 5-15 minutes thereafter, until it has been determined that the sound level measurement system has not significantly drifted from its calibrated level. Once this fact has been established, calibrations may be made at intervals once every hour. A significant drift shall be considered to have occurred if a 0.3 dB or more excursion is noted from the system's predetermined reference calibration level. In the case of systems using displays with whole decibel increments, the operator may visually judge when the 0.3 dB drift has been met or exceeded. Code of Federal Regulations11
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