B&K 2250 Light Manual do Utilizador descarregar pdf (Página 71)

CHAPTER 5

Calibration

Fig.5.8 Charge Injection Calibration. Low-leakage resistance capacitor C

is set in parallel with the

microphone and fed with voltage e

. The ratio e

is constant when g, C

, C

and C

are

constant. Changes to preamplifier gain (g), cable parameters, microphone capacitance

), etc., will change e

and, hence, indicate probable changes in calibration

5.10.2 Performing a Manual CIC with your Type 2250/2270

CIC is only available for microphones connected to the Top Socket of the Analyzer and with

Logging Software BZ-7224 and Enhanced Logging Software BZ-7225.

Tap the Main Menu icon and select Calibration from the list. Click the CIC tab to view

the various CIC parameters that are available. The available parameters will include the results

of the latest manual CIC, together with the reference (Fig.5.9).

The Status Field at the top of the screen informs you how to perform the CIC.

Press the Start CIC button to start the CIC. After approximately 10 sec you will see the result.

Normally, the CIC Reference Ratio is set the very first time a CIC is performed, however, you

should update the CIC Reference Ratio if you change the microphone preamplifier. You do this

by checking the Use as new Reference checkbox.

The CIC Reference Ratio and CIC Ref. Date parameters display the results of the very first

manual CIC, and this will be used as the ‘reference’ for all subsequent CIC Ratio

measurements.

Note: Each microphone in the transducer database has a CIC Reference Ratio.

If the CIC Ratio parameter deviates by more than 0.5 dB from the CIC Reference Ratio, there

may be a problem, and it should be investigated, see page 60.

Preamplifier

Microphone

Cable Generator

= g

+ C

( )

970294/1

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B&K 2250 Light Manual do Utilizador Página 71