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GRAS 90CA Instruction Manual

Microphone calibration system
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Instruction Manual
90CA Microphone Calibration System

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  • Page 1 Instruction Manual 90CA Microphone Calibration System...
  • Page 2 Revision History Any feedback or questions about this document are welcome at gras@gras.dk. Revision Date Description 15 October 2009 First publication of this document 01 March 2012 Redesign of the manual. Added information about calibration in general, calibration of microphone sets, and preamplifiers.

  • Page 3: Table Of Contents

    How often should I calibrate? ..............8 The Concept of the 90CA Microphone Calibration System ..... 9 Applications .................... 10 The Basic Principles of 90CA: Microphone Calibration in Four Easy Steps ..11 Functional Block Diagram ................. 12 Hardware and Software for Level Calibration ..........13 Hardware and Software for Frequency Calibration ........
  • Page 4 Calibrating Microphones and Microphone Sets ........39 Starting the System ................. 39 Step 1: Registering the Microphone ............41 Step 2: Performing a Level Calibration............42 Step 3: Performing a Frequency Response Calibration ........45 Step 4: Storing Calibration Results ............46 Calibrating a Preamplifier .............

  • Page 5: Introduction

    Using This Manual Inside this manual, you will find A description of the principles of the 90CA calibration system, with an overview of the hardware and software for the different types of calibration in “” on page 8. Diagrams and instructions for assembling and connecting the hardware for both the PXI and the PCI version of 90CA “Assembling and Connecting the Hardware”...

  • Page 6: Introduction To Calibration

    Introduction to Calibration For making documented, traceable, and approved measurements, your measurement equipment must be calibrated. Basically, calibration is a method that establishes the relationship between a measuring device and its measurement units. This is done by comparing a device or the output of an instrument to a standard with known characteristics.

  • Page 7: Which Type Of Calibration Do I Need

    Traceable Calibration An instrument has a traceable calibration if the measurement instrument used for performing the calibration is traceable to national or international institutes / standards through an unbroken chain of comparisons all having stated uncertainties. Accredited Calibration An instrument has an accredited calibration if the calibration is performed by an approved accredited calibration laboratory.

  • Page 8: How Often Should I Calibrate

    How often should I calibrate? How often you should calibrate your equipment depends on the type of measurements as well as on your quality assurance system. Use the following guidelines to determine when calibration is needed: • When you receive a new instrument •...

  • Page 9: The Concept Of The 90Ca Microphone Calibration System

    • IEC 61094-6 An optional module for calibration of preamplifiers is available. The 90CA is delivered with ready-to-use software and hardware, as well as preinstalled test parameters for G.R.A.S. microphones and preamplifiers. The 90CA is available in two versions: a PXI-based version with boards for mounting in a NI PXI Express chassis and a PCI-based version with boards for use in a PC.

  • Page 10: Applications

    Applications You can use the 90CA Microphone Calibration System for all types of IEC-standardized ⁄ “, ¼” , ½”, and 1” measurement microphones to perform. • Level calibration of microphones using a pistonphone and the insert voltage technique • Frequency calibration of microphones using an electrostatic actuator Note: For microphones with a non-removable protection grid, frequency calibra- tion is not feasible.

  • Page 11: The Basic Principles Of 90Ca: Microphone Calibration In Four Easy Steps

    The Basic Principles of 90CA: Microphone Calibration in Four Easy Steps The 90CA Microphone Calibration System was designed to eliminate the risk of operator errors during calibration. The workflow is simple and straight-forward with its four steps as shown in the following figure.

  • Page 12: Functional Block Diagram

    Calibration Certificate Fig. 6. The complete microphone calibration system represented by functional blocks A overall functional block diagram of the 90CA has four areas as explained here. The Level Calibration Equipment block covers the components needed to determine the microphone’s open-circuit sensitivity [mV/Pa].

  • Page 13: Hardware And Software For Level Calibration

    AL0017 Signal Conditioning, Power, and Switching Fig. 7. Functional block diagram of the 90CA hardware and software for level calibration The hardware and software for level calibrations are introduced here. Level Calibration Equipment • Pistonphone 42AP: A well-defined sound level reference (sound source); it is automatically switched on/off via a COM port, and it automatically reads the static air pressure.

  • Page 14: Hardware And Software For Frequency Calibration

    Signal Conditioning System Controller Fig. 8. Functional block diagram of the 90CA hardware and software for frequency calibration The block diagram for frequency calibration is similar to the diagram for level calibration. The details are the same for the system controller and the power, signal conditioning,...
  • Page 15 Frequency Calibration Equipment • ¼” Preamplifier 26AB (¼” -to-½” adapter AF0008 supplied) OR (not shown) ½” Preamplifier 26AK; both amplifiers with integrated 7-pin LEMO connector. • ½” Electrostatic Actuator RA0014: for testing the frequency response of stan- dard ½” and ¼” microphones; an adapter is included for testing ¼” microphones; can be connected directly to the Actuator Supply 14AA.

  • Page 16: Delivered Components

    Delivered Components The 90CA Microphone Calibration System includes all accessories for calibrating micro- phones from G.R.A.S. Packing List for the 90CA Please note that the included hardware from Natinal Instruments may be newer and improved versions with different product designations than those listed here.

  • Page 17: Assembling And Connecting The Hardware

    Box, and the 12AQ Power Module can be placed as far away from the other equipment as the available cable lengths allow. The following pages show how the components of the 90CA are connected for calibra- tion of microphones—both externally polarized and prepolarized (CCP), externally polarized microphone sets, and prepolarized microphone sets.
  • Page 18 G.R.A.S. Type xxxx...

  • Page 19: Pxi: Connections For Test Of Microphones (Ext. Pol. And Prepol.)

    PXI: Connections for Test of Microphones (Ext. Pol. and Prepol.) Important: All electrical devices must be switched off while you are setting up the 90CA. Use the gray 50-position ribbon cable to connect the 6509 Digital I/O card to the “Control Signal”...

  • Page 21: Pxi: Connections For Test Of Externally Polarized Microphone Sets

    PXI: Connections for Test of Externally Polarized Microphone Sets Important: All electrical devices must be switched off while you are setting up the 90CA. Use the gray 50-position ribbon cable to connect the 6509 Digital I/O card to the “Control Signal” socket on Switch Box RA0192 (socket on the rear).

  • Page 23: Pxi: Connections For Test Of Prepolarized Microphone Sets

    PXI: Connections for Test of Prepolarized Microphone Sets Important: All electrical devices must be switched off while you are setting up the 90CA. Use the gray 50-position ribbon cable to connect the 6509 Digital I/O card to the “Control Signal” socket on Switch Box RA0192 (on the rear).
  • Page 24 G.R.A.S. Type xxxx...

  • Page 25: Pci: Connections For Test Of Microphones (Ext. Pol. And Prepol.)

    PCI: Connections for Test of Microphones (Ext. Pol. and Prepol.) Important: All electrical devices must be switched off while you are setting up the 90CA. Use the gray 50-position ribbon cable to connect the 6503 Digital I/O card to the “Control Signal”...

  • Page 27: Pci: Connections For Test Of Externally Polarized Microphone Sets

    PCI: Connections for Test of Externally Polarized Microphone Sets Important: All electrical devices must be switched off while you are setting up the 90CA. Use the gray 50-position ribbon cable to connect the 6503 Digital I/O card to the “Control Signal” socket on Switch Box RA0192 (socket on the rear).

  • Page 29: Pci: Connections For Test Of Prepolarized Microphone Sets

    PCI: Connections for Test of Prepolarized Microphone Sets Important: All electrical devices must be switched off while you are setting up the 90CA. Use the gray 50-position ribbon cable to connect the 6503 Digital I/O card to the “Control Signal” socket on Switch Box RA0192 (on the rear).

  • Page 30: Assembling The 90Ca

    Assembling the 90CA This section describes the assembly of the stands for the 90CA, as well as the mounting of the microphones, preamplifiers, and accessories. Assembling the Calibration Stand Mount the preamplifier onto the pistonphone calibration stand: Using the cable labeled 12 or 12A in the electrical connections diagrams on the previous pages, connect the preamplifier to the input of the RA0192 Switchbox.
  • Page 31 Actuator Stand Assembly Insert the preamplifier into the actuator calibration stand AL0010 Secure the preamplifier with the grub screw/finger screw (shown in the following figure) Preamplifier Grub screw/finger screw Socket for plug on electro-static actuator To Actuator Supply 14AA LEMO plug of preamplifier to Switch Box Connect the actuator to the “+800 V DC”...

  • Page 32: Settings For The Instruments Included In The System

    Microphones with non-removable protection grid Frequency calibration is not feasible for microphones with non-removable protection grids. Powering on the 90CA Connect the power cable and power supply for each device. Turn on the power for each device.

  • Page 33: Mounting The Microphones

    Mounting the Microphones ⅛" Externally Polarized and Prepolarized G.R.A.S. Microphones All the items you need for level and frequency calibration of an ⅛” G.R.A.S. microphone are shown on this page. Level Calibration 26AN Preamplifier, insert voltage RA0063 ⅛” to ¼” Adapter ⅛”...
  • Page 34 ¼” Externally Polarized and Prepolarized G.R.A.S. Microphones All the items you need for level and frequency calibration of an ¼ ” G.R.A.S. microphone are shown on this page. Level Calibration 26AN Preamplifier, insert voltage ¼” microphone (DUT) RA0049 ¼” to ½” (Pistonphone) Adapter G.R.A.S.
  • Page 35 ½” Externally Polarized and Prepolarized G.R.A.S. Microphones All the items you need for level and frequency calibration of an ½ ” G.R.A.S. microphone are shown on this page. Level Calibration 26AG ½” Preamplifier, insert volt- age (26AN ¼” Preamplifier, insert voltage can be used with G.R.A.S.
  • Page 36 1” Externally Polarized G.R.A.S. Microphones All the items you need for level and frequency calibration of an ⁄ ” G.R.A.S. microphone are shown on this page. Only the Device Under Test is not included. Level Calibration 26AG ½” Preamplifier, insert voltage 1”...

  • Page 37: System Verification

    The 90CA calibration system has been tested by G.R.A.S. Sound & Vibration and is delivered with a test certificate for the complete system, specific instruments, and their serial numbers listed. The 90CA is a very stable system that will calibrate to very tight tolerances.

  • Page 38: Introducing The Calibration Software Sw0002

    Introducing the Calibration Software SW0002 The 90CA is delivered with the software preinstalled. It can be launched from the desktop as with any Windows application. IMPORTANT. If you decide to install a new version of LabView, DO NOT uninstall the version that comes with the system, because if you do, the calibration software will not work properly, or at all.

  • Page 39: Calibrating Microphones And Microphone Sets

    Measured data for the level calibration is displayed here. Measured data for the frequency calibration is displayed here. In general, the indicators are green when the measurement is within the preset limits and red when the the measurement is outside the limits. Calibrating Microphones and Microphone Sets This section describes how to do a calibration of a microphone or microphone set.
  • Page 40 Enter Test Conditions: Enter your name or other identification here. The 42AP pistonphone supplies this information automatically. If the 42AP is not connected to the COM port, enter the barometric pressure [hPa] manually, e.g. “1005”. Type in the temperature [°C], e.g. “22 “. Type in the relative humidity [%], e.g.

  • Page 41: Step 1: Registering The Microphone

    Step 1: Registering the Microphone Click New Calibration and the Test Details dialog box opens. Select a microphone type from the list, enter serial number, Calibration ID, and Customer ID (if needed). The Microphone Manufacturer name is defined in the Microphone Definition File. The Additional Remarks are for any special remarks, such as front cavity height and diameter of a 40AU LS2aP microphone.

  • Page 42: Step 2: Performing A Level Calibration

    Step 2: Performing a Level Calibration Mount the microphone onto the preamplifier: • 26AG for ½” microphones • 26AN for ¼” microphones Place the microphone into the pistonphone 42AP . Note: Make sure the microphone is inserted all the way into the coupler. In the main menu, click Level calibration.
  • Page 43 The software measures the difference between open-circuit and closed-circuit sensitiv- ity. The test has two different steps which appear automatically; first, a closed-circuit sensitivity measurement, and then an insert-voltage measurement to measure the open-circuit sensitivity. In the first step, the closed circuit sensitivity measurement – two curves, gradually converging –...
  • Page 44 The amplitude scale (C) is initially set to 10 dB. As the curves approach each other, it is recommended to downscale first to 1 dB, and finally to 0.1 dB: When the signals have stabilized (A), click STOP (B). Then, a new window opens and the software switches off the pistonphone (pistonphone LED red) and starts measuring the open-circuit sensitivity by the insert voltage method.

  • Page 45: Step 3: Performing A Frequency Response Calibration

    Step 3: Performing a Frequency Response Calibration Mount the microphone onto the preamplifier in the AL0010 Frequency Calibration Stand Carefully unscrew the microphone protection grid. Place the electrostatic actuator onto the microphone diaphragm In the software main menu, click FreqCalibration and a new window opens. This window has a menu bar with the following features: Measurement, Test limits, Setup, and Debug.

  • Page 46: Step 4: Storing Calibration Results

    To store the data measured, click Save Data. The data will be stored at a path defined in the Microphone Definition File. To generate a calibration certificate, click Print. Note: The 90CA does not include a printer. You must install a printer to print certificates. Fig. 12. Typical G.R.A.S Calibration Chart...

  • Page 47: Calibrating A Preamplifier

    This section describes how you set up the system for calibration of the preamplifiers and walks you through a typical calibration workflow. Note: Calibrating preamplifiers is an option package for the 90CA. (Option OP0020). All preamplifiers except insert-voltage preamplifiers and preamplifiers with SysCheck can be calibrated with the 90CA.

  • Page 48: Step 1: Registering Test Conditions

    Step 1: Registering Test Conditions In preparation for your calibration, Disconnect all cables on the front panel of the RA0192 switchbox. Connect the 42AP pistonphone to the power module and turn on the pistonphone. On your PC desktop, start the preamplifier calibration by double-clicking the PreAmp calibration icon to open the software control panel.
  • Page 49 Fig. 13. The 90CA main window for preamplifier calibration This main window is where you can • Start a new calibration • Measure the noise floor (linear and A-weighted) • Edit the customer ID • Measure the frequency response • Edit the test conditions •...
  • Page 50 Enter the serial number for the preamplifier. The remaining fields are optional and can be used to suit your classification system. Additional information can be valuable when you have a large amount of calibration data in your archives. Click OK; this window closes and you return to the main screen. Measure the DC Voltage (Skip this step for preamplifiers with integrated cables.) Connect a cable to the RA0192 system switchbox connector called “Preamp.

  • Page 51: Step 2: Frequency Response

    Verify the Self Noise of the Preamplifier With the same hardware setup as for the DC voltage measurement, you can measure the self noise of the preamplifier. On the main window (the software panel), press Noise. A new window opens and the noise measurement starts automatically.

  • Page 52: Step 3: Lemo Reference Level Test

    Step 3: LEMO Reference Level and Sensitivity Test Measuring the LEMO reference level is a necessary step before measuring the sensitivity. Remove the RA0062 from the preamplifier (and GR0010, if used). Remove the preamplifier and its cable from the switchbox. Connect the reference preamplifier (26AG), the reference microphone (40AG), and the cable (AA0008) to the “Preamp.

  • Page 53: Step 4: Storing Calibration Results

    Step 4: Storing Calibration Results You must save and store the results before you can print a calibration sheet. On the main window, click Save Data. This stores the data from all the tests in a text file (.txt) on the hard drive. The filename is generated from the preamplifier type and the serial number of the preamplifier.

  • Page 54: High Frequency Calibration

    High Frequency Calibration For high frequency calibration of microphones, microphone sets, or preamplifiers, you must use a signal generator and a digital multimeter capable of dealing with high frequencies, for example these models provided by Keysight, or instruments with similar specifications: •...
  • Page 55 Calibrate the device as usual; the system automatically switches between using the data acquisition card in the computer and the external signal generator and the multimeter. The “Cut-off Frequency” entered in the setup file must be included in the frequency list in the definition file.

  • Page 56: Working With The System Files And Documentation

    Working with the System Files and Documentation There are several files used by the 90CA that you can edit. This section describes the location of those files and how you can edit and store them. Viewing and Editing the Microphone and Preamplifier Definition Files All the microphone and preamplifier definitions used by the 90CA are stored in the “Microphone Definition file”...
  • Page 57 Fig. 14. The microphone definition file This screenshot shows a section of a microphone definition file. The following two lists explain the details of the files for microphones and for preamplifiers. Data in the Microphone Definition List Identify the microphone with The microphone’s type number, such as 40AB, in Mic Name of the microphone Type, as in free field (F), pressure (P), random incidence (R), or other (O)
  • Page 58 14. DIAdem report file – Location and file name of the DIAdem report template (.tdr) 15. PDF storage path – Where the 90CA stores the calibration files (as PDFs) 16. DIAdem script file – Location and file name of the DIAdem system file used for printing out the calibration sheet 17.

  • Page 59: Setup.txt: The Microphone Calibration System Setup File

    28. Lower Mag – Lower limit for frequency response in dB Setup.txt: The Microphone Calibration System Setup File When you start up the SW0002 Calibration Software for the 90CA, the software reads the text file called setup.txt. Therefore, the location and contents of this file are critical.
  • Page 60 Start the Microphone Calibration System Software, Navigate to the “Setup” Tab The path is listed in the “Default Directory” field. Fig. 15. The edit Setup window If the file is deleted or moved from the default directory, the system will prompt for the necessary information and create a new Setup.txt file.
  • Page 61 • DAQmx Device Name 6503 (6509 for PXI-based system) – The name of the NI 6503 board (PXI: 6509) as defined in the National Instruments Measurement and Automation Explorer • Method to obtain the Barometric pressure There are four different settings to choose between: “Type in Manually” where you enter the barometric pressure manually, “42AP Pistonphone Barometer”...

  • Page 62: Editing The Calibration Charts In Diadem

    Click Print in the 90CA software program and the calibration data is transferred to the DIAdem Data Portal. (The 90CA provides only the data listed in the Data Portal.) The data from the Data Portal is inserted into the Calibration Certificate with DIAdem expressions.
  • Page 63 The calibration certificate is two pages. The first page displays the frequency response, the second page contains all the data. Fig. 17. Calibration certificate, page 2 For more information about the functions of DIAdem and the syntax of the DIAdem expressions, see the Quick Tour in DIAdem Help.

  • Page 64: The File Structure On The System Controller

    Note: Do not edit or modify the file in any way or the system will report an error. If the file is modified or deleted, or you receive any errors, contact support at gras@gras.dk...
  • Page 65 Uncertainty Calculations The Uncertainty Calculation spreadsheet lists the calculated system uncertainty for each type of microphone and for the individual parameters such as • Volume correction • Sensitivity • Pressure • Noise • Humidity • Polarization voltage • Temperature • Capacity This information can also be compared to the National Physical Laboratory uncertainty.

  • Page 66: Warranty And Maintenance

    Warranty and Maintenance The 90CA is assembled and tested by G.R.A.S. before leaving the factory. An individual test certificate is included with each 90CA. Warranty All G.R.A.S. products are made of high-quality materials that will ensure life-long stabil- ity and robustness. The 90CA is delivered with a 2-year warranty.

  • Page 67: Service And Repairs

    The diaphragm is a 2-micron thick metal foil, so any fluid that doesn’t damage stainless steel can be used. Be very careful during cleaning because the diaphragm is extra fragile in that situation. Sometimes you cannot see that the diaphragm is dirty. It is only when connected to the electrostatic actuator that you can measure that something is disturbing the vibration.

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