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 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), 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.
A stable CIC Ratio means a ‘healthy’ system and assures stable operation of microphone, cable, preamplifier and the remaining measurement system.
Fig.5.8 Charge Injection Calibration. Low-leakage resistance capacitor Cc is set in parallel with the microphone and fed with voltage ei. The ratio eo/ ei is constant when g, Cc, Cm and Ci are constant. Changes to preamplifier gain (g), cable parameters, microphone capacitance (Cm), etc., will change eo/ ei, and hence indicate probable changes in calibration
Cm Cc
Ci R1
Preamplifier
Microphone Cable Generator
g
ei eo
eo ei
Cc
= g
( )
Cm + Ci + Cc970294/1
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Calibration 49
5.7.2 Performing a Manual Charge Injection Calibration with the Analyzer
Charge Injection Calibration is only available with Logging Software BZ-7133.
Tap > 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 s 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.
✐
Please 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.
Fig.5.9 CIC tab
The result of the Charge Injection Calibration consists of four parameters:
• CIC Ratio
• CIC Ratio Date
• Deviation from Reference
• CIC Result
The CIC Result can be Passed’, Background noise too high or CIC Ratio deviates from Ref.
51
Chapter 6
Data Management
This chapter describes data management, including:
• Job and project organization
• Setting the default job folder
• Recalling measurements
• Uploading to Measurement Partner Cloud (MP Cloud)
6.1 Organizing Measurements 6.1.1 Description of Jobs and Projects
When saving a set of measurement results, they are organized together with setup information, calibration information, annotations and signal recordings in a project.
A project contains the following:
• Measurement results:
– Broadband values (for example, LAeq, LAFmax, LAFmin)
– Frequency spectra (if 1/1-octave or 1/3-octave Frequency Analysis Software for 2250 Light, BZ-7131/32 are enabled on your analyzer and you have selected a Frequency Analyzer template)
• Weather and GPS data
• Measurement Setup
• Display Setup (parameters you have selected)
• Information on the microphone
• Calibration
• Signal Recordings (attached to measurements as required)
The project name is automatically created by combining the Project Name Prefix with a number (starting from 001), that is, Project 001 for the first project, Project 002 for the next, etc.
To rename the Project Name Prefix:
1) Navigate to the project (tap > Explorer).
2) Tap the name of the project (tapping the icon opens the project immediately) 3) Tap Rename and enter the new project name.
Projects are saved in folders, which are called ‘jobs’ on your analyzer. These are similar to folders in the Microsoft® Windows® filing system.
Jobs can be created:
• In the internal memory
• On a Secure Digital (SD) card
• On a USB memory stick (G4 analyzers only)
• On a Compact Flash (CF) card (G1 – 3 analyzers only)
6.1.2 Navigating in Jobs
A results browser called Explorer is used to navigate through the jobs and projects.
To view all jobs and projects, tap > Explorer or tap the project name on the Measurement screen. A screen similar to Fig.6.1 will appear.
Fig.6.1
The Explorer screen
The example in Fig.6.1 displays a list of jobs and then some projects, which have not been stored under a job name.
The topmost line in the status area (Internal Disk\ in Fig.6.1) shows the location in the memory.
The next line in the status area contains 4 icons for navigation.
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Data Management 53
Tap to go up one level in the job levels. The top level is the Memory level, where physical memory devices can be selected. You can select:
• With G1 – 3 analyzers:
– Internal Disk
– SD-Card (if a card is inserted in the SD slot) – CF-Card (if a card is inserted in the CF slot)
• With G4 analyzers:
– Internal Disk
– SD-Card B (if a card is inserted in the bottom SD slot) – SD-Card T (if a card is inserted in the top SD slot)
– USB-Mem (if a memory stick is inserted in the USB Standard A socket)
To go down one level (that is, exit the Memory level), tap on the job name (Internal Disk in this case) and select Open from the drop-down list or tap Memory , next to Internal Disk.
Tap to create a new job folder. The first job folder name will be Job 01, subsequent job folders will be labelled Job 02, Job 03, etc. You can rename the job folder name by tapping on the name and selecting Rename from the drop-down list. Use the keyboard to key in a new name – accept by tapping Enter .
To go down one level (open a job), you tap the job name in the list and select Open from the drop-down list or tap the job icon to the left of the job name.
You can move a job/project (and its content) to another job by tapping the job name/project name and selecting Cut from the drop-down list. Then navigate to the job you want as the new holder of the moved job/project and tap on Paste , or navigate to the level above and tap on the job name and select Paste from the drop-down list.
In order to copy a job/project do as described above, but use Copy instead of Cut from the drop-down list.
Select Delete from the drop-down list in order to delete the job/project and all of its contents.
You can select more than one job/project for copy, cut or delete by tapping and holding the stylus on a job/project name and then dragging the stylus up or down to select other jobs/projects.