Be it for ISO like compliance, or just to make sure, instrumentation needs to be recalibrated frequently.

In our lab, we use reference sensors that are recalibrated annually at an accredited lab.

Left high frequency calibration and right low frequency calibration

Acoustic particle velocity sensors can be calibrated 20Hz - 20kHz
Sound pressure levels can be calibrated 20Hz - 20kHz

Normally, using express services, turnaround time of recalibration services is one week. 

For more info, contact: test@microflown.com