61 Calibrate
Calibration screen
Models SE and DL
3M recommends calibrating your Verifier before you r un a STI-PA
measurement and after to ensure highly accurate m easurement results.
The microphone should be calibrated before use for a number of reasons.
First, the microphone is sensitive to humidity and pres sure changes.
Calibrating before taking measurements assures t hat your level
measurements are accurate for the current environm ent. Performing a
calibration verification (post-cal) allows you to verif y that conditions have not
significantly affected your readings.
Calibrating also serves the dual purpose of check ing the microphone for
significant damage, such as a torn or contaminate d diaphragm.
You can calibrate the instrument in the field with ref erence to the output of a
calibrated sound source. 3M offers a line of acoustic c alibrators that are
available (such as the QC10/20).
Calibration screen
The Calibration screen contains a calibration optio n, called Calibrate, and a
Calibration History. The history shows Pre-Calibrati on (Pre-Cal) and Post-
Calibration (Post-Cal) results for previous calibrat ions, as applicable. For
each calibration type, the resulting SPL level is sho wn along with the time
and the date of the calibration.
Pre-Calibration
The main reason to calibrate is to adjust t he current microphone reading to
match a reference input, usually provided by a calibr ator.
A Pre-Calibration is conducted when the session is stopped. When you
calibrate during a stopped session, the new calibrat ion results replace the
previous Pre-Calibration results and the Post-Calibrati on results are
removed. You will always see the last Pre- Calibrat io n res ults .
Post-Calibration
A post-cal is really a calibration verification; that is, it does not change the
instrument’s calibration. It compares the microphone's current level with the
value read from the last calibration (assuming that the same source is used).
A Post-Calibration is a calibration done during a session pause. When you