B&K 2250 Light, User Manual, Page: 55 / 208

CHAPTER 5
Calibration
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• Send your instrument for Accredited/Traceable Calibration and update the Last
Calibration date
• Check the ‘ Do not ask/remind again ’ checkbox in the reminder pop-up (see example in
Fig.5.7)
• Disable the automatic calibration reminder
Fig.5.7
Reminder pop-up
You can set the Calibration Interval parameter to either 12 months or 24 months depending on
your local requirements.
You can disable the facility by selecting the Automatic Calibration Reminder parameter to Off .
5.6 Charge Injection Calibration
5.6.1 Theory of CIC
If an external sound source is not available, for example during short or long term monitoring,
you can check the calibration of the analyzer using the Charge Injection Calibration (CIC)
facility. This is done automatically during a logging measurement (see section 11.2). Unlike an
internal calibration, the Brüel & Kjær patented CIC technique enables a complete
measurement chain to be verified, including the microphone, the preamplifier, the cabling and
the analyzer. Each verification measurement is compared to an initial reference measurement.
As the name implies, the method uses injection of charge into the microphone and preamplifier
input circuit, and the ratio between the measured signal and the injected signal is measured
(CIC Ratio), see Fig.5.8.
The method is based on detection of changes in impedance at the input terminal. It was
developed for monitoring of microphone channels and requires a preamplifier with a small,
extremely stable, built-in capacitor which makes it possible to apply an electrical signal to the
preamplifier (and microphone) input terminal.