B&K 2250 Light Manual do Utilizador descarregar pdf (Página 70)

Hand-held Analyzer Types 2250 and 2270 – User Manual

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.

5.10 Charge Injection Calibration

5.10.1 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 and section

12.2). Unlike an internal calibration, the Brüel & Kjær patented CIC technique enables a

complete measurement chain to be verified, including the microphone, preamplifier, cabling

and analyzer. Each verification measurement is compared to an initial reference measurement.

As the name implies, the CIC method injects an internally generated charge into the

microphone and preamplifier input circuit, and the ratio between the measured signal and the

injected signal is measured (CIC Ratio; Fig.5.8).

This method is based on the 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 enables the application of an electrical signal to a

preamplifier (and microphone) input terminal.

A stable CIC Ratio means a ‘healthy’ system and assures stable operation of the microphone,

cable, preamplifier and remaining measurement system.

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B&K 2250 Light Manual do Utilizador Página 70