Manual Analysis Software AFD 1201

Transcription

1 AFD AcoustiTube Manual Analysis Software AFD 1201 Measurement of Transmission loss acc. to Song and Bolton 1

2 Table of Contents Introduction - Analysis Software AFD AFD AcoustiTube - Measuring Set-up... 5 Setup - Setting of Property Values... 7 Microphone - Calibration of Microphones Signal to Noise Ratio - Adjustment of Amplifier Channel Correction - Correction of Measuring Signals with respect to Channel Noise Measurement - Determination of material parameters Postprocessing - Averaging of Multiple Measuring Results Database - Reliable data management

3 Introduction - Analysis Software AFD 1201 The "AFD AcoustiTube " together with the analysis software "AFD 1201" is a very efficient tool for determining the transmission loss, the sound transmission coefficient, the progagation loss, the complex impedance and the complex wave number of specimens in the laboratory. Its working principle is based on the transfer-matrix method of Song and Bolton. Before an overall measurement can be carried out a couple of different adjustments are to be made, that are described on the following pages. Warnings: Do not use the AFD AcoustiTube with any other than the specified amplifier! Do not use any other than the specified type of microphone! Do not remove any parts of the AFD AcoustiTube! Do not disconnect any internal wires or electrical components! Be sure to connect the red wire between speaker and amplifier to the red terminal (+) of the amplifier, and the black wire to the black terminal (-) of the amplifier! Reduce the output level of the amplifier if the overload warning message is displayed on screen or the overload LED of the amplifier illuminates! Please pay attention to sharp-edged parts of AFD AcoustiTube and the sharpened hollow punches! The Gesellschaft für Akustikforschung Dresden mbh is not responsible for damages resulting from incorrect handling or any modifications done to the AFD AcoustiTube! The Gesellschaft für Akustikforschung Dresden mbh is not responsible for any indirect loss or damage resulting from any data loss or failure of the software. It is recommended to backup your database content periodically. See docs/8.3/static/backup.html 3

4 For any further information please contact us: Gesellschaft für Akustikforschung Dresden mbh Blumenstraße Dresden Phone: +49 (0)351 / Fax: +49 (0)351 / info@akustikforschung.de Internet: 4

5 AFD AcoustiTube - Measuring Set-up Before the transmission loss and other parameters of a material can be measured, the AFD 1200 AcoustiTube needs to be set up as shown in the following figures. It is recommended to place the AFD AcoustiTube straight on a plane surface to guarantee accurate connection between the tube sections and precise measurement results. 5

6 The picture below shows in detail how to put the specimen into AFD AcoustiTube. 6

7 Setup - Setting of Property Values The first step in using the analysis software AFD 1201 is the setup of various property values. This includes the definition of: the environmental temperature in C, the atmospheric pressure in kpa, the relative atmospheric humidity in %, the lower frequency limit of the evaluated frequency range in Hz, the upper frequency limit of the evaluated frequency range in Hz, the Riemann frequency in Hz, which is necessary for the precise computation of the complex wave number and the sound velocity the number of averages carried out during the measurement, determining the precision of the measuring result, the distance z1 between the front of the material sample under test and the microphone one in mm, the distance z2 between the front of the material sample under test and the microphone two in mm, the distance z3 between the front of the material sample under test and the microphone three in mm, the distance z4 between the front of the material sample under test and the microphone four in mm, the diameter of the specific AFD AcoustiTube in mm as well as the length of the material sample under test in mm. On the right of the screen you can chose if a cutoff Algorithm will be applied or not. Most samples can be measured without using a cutoff. But sometimes, e.g. if you carry out a measurement without a sample, it might be necessary to suppress errors that are caused by noise and are propagated during the calculation. In this case check use Cutoff and chose a proper Cutoff value. 7

8 Selecting the button Extended Settings allows the definition of the sensitivity of the microphones used. Depending on the data acquisition used, either IEPE condition or 200 volt usage can be chosen. The calibration frequency and the sound pressure level used for the calibration can be set as well. Furthermore the sampling rate and the sample length can be defined. For example: a greater sample length causes higher frequency resolution. Please note when changing the sampling rate: The upper frequency is limited according to the AcoustiTube used. This frequency must not be higher than half of the sampling rate. After pressing the Ok button, the hardware will be rebooted. The default property values shown in the picture above are stored in a configuration file that is loaded at the start of the software. You can apply or create an own configuration file by using the File menu at the top of the screen. 8

9 Depending on the user's choice a typical file dialog opens that requires the name of an *.xml-file to be loaded or to be saved. 9

10 Microphone - Calibration of Microphones The next step deals with the calibration of the microphones used. The calibration can be started by pressing the Run button after placing the microphone in the working calibrator. The sound pressure level is measured and averaged over a certain time interval. The Stop button allows cancelling the calibration. The measuring result is shown right next to the calibrated microphone. The spectrum of the measured calibration signal is visualized in the diagram below. If the sound pressure level differs more than a defined value (in general 2 db) from the calibration sound pressure level (in general 94,0 db) a pop-up window appears, telling the user to repeat the calibration. 10

11 Otherwise the calibration is defined as "successful", the sound pressure level difference (Gain) shown on the right is further used to correct the measured microphone signal. It is possible to save the calibration as part of the configuration by following the steps explained in Setup. 11

12 Signal to Noise Ratio - Adjustment of Amplifier The third folder contains the adjustment of the amplifier by verifying a high signal to noise ratio. The signal to noise ratio is defined as the difference between the sound pressure level occurring at the microphones under test conditions and the background noise level. After putting a typical material sample in the specimen holder, the measurement of the background noise can be started by pressing the left Run button. The measuring result is shown in the diagram below. The progress of the measurement is depicted by the measurement bar. With the help of the Stop button the measurement can be finished before the number of averages is reached. A test measurement can be started by pressing the right Run button. The result is added to the diagram below, visualizing the sound pressure level difference of both measurements over the whole frequency 12

13 range. The legend right next to the diagram informs about the colors belonging to the different curves. By pressing the Stop button this measurement can also be finished before the number of averages is reached. The sound pressure levels of the Background Noise and the Signal at 1000 Hz are shown on the right of the Stop button respectively. As a result of both measurements, the calculated signal to noise ratio for the 1/3-octave band of 1000 Hz is shown above the diagram's legend. Attention: For a precise measurement the signal to noise ratio should be at least 40 db over the whole frequency range. This constraint can be achieved by adjusting the amplifier. If the sound pressure level at the microphones gets to high, an Overload warning appears in red letters. By clicking on Coherence right next to SNR another diagram is shown. 13

14 The coherence reveals the dependency of two signals. If there is a linear dependency, the coherence turns to 1. The diagram visualizes the coherence between two microphone signals respectively. Attention: For a precise measurement the coherence between the signals should be very close to 1 over the whole frequency range. 14

15 Channel Correction - Correction of Measuring Signals with respect to Channel Noise The fourth section is a control panel for correcting the measuring signal with respect to channel noise caused by the microphones and the connected transfer paths. The idea of correcting this noise is to carry out four different measurements under the same measuring conditions except for the positions of the microphones - that means one measurement with original microphone positions and three further measurements with the same conditions but interchanged microphones. Attention: It is recommended to carry out the channel correction after having put an absorber sample (maybe a specific calibration sample) into the specimen holder. With respect to not forgetting to change back the microphones after the correction, the software was designed to start with the measurements using interchanged microphones. After having put the specific calibration sample into the specimen holder, the first measurement can be started by pressing the left Run button. 15

16 Before the measurement is carried out a pop-up window opens to point out the interchanged microphones. The progress of the measurement is depicted by the measurement bar, the measured transfer function H12'' is shown in the diagram below. It is necessary, that the measurement will be finished without pressing the cancel button to get to the next step. Now the second measurement can be started by pressing again the Run button. Another pop-up window opens to point out to change microphone 1 and microphone 3. Attention: It is necessary to put microphone 2 to its original position before further interchanges. Again, the measured transfer function H13'' is shown in the diagram below. Also here, it is necessary, that the measurement will be finished without pressing the cancel button to finish the measurement. The progress of the overall measurement of the transfer functions is depicted by the measurement bar on the right. 16

17 The measurement of the transfer function H14'' can be carried out in the same manner. H14'' is then shown in the diagram. Now the fourth measurement can be started by pressing the Run button. A pop-up window opens to point out to put the microphones back to the original positions. 17

18 After successful measurements, channel correction matrices Hc are computed and can be stored. A pop-up window appears to decide wether to Discard, Save, Save + Use and Use the computed correction matrices. It is possible to load already existing correction matrices by using the File menu. The correction matrices used (together with the defined distances z) are shown in the status line and is applied automatically to all further measurements to correct the microphone signals with respect to channel noise. In case of changing any distances z in Setup, the corresponding value in the status line turns red to indicate that a new channel correction is necessary. It is recommended to carry out the channel correction once a day before a measuring campaign. Attention: In case of changing the microphone distances or using AcoustiTube of other diameters, the channel correction has to be carried out again. 18

19 Measurement - Determination of material parameters The fifth tab represents the main program - the measurement of Transmission loss, Sound Transmission Coefficient, Propagation loss, Complex Impedance, Complex Wave Number and Sound Speed and it gives a graphical representation of the results. At first a measurement object needs to be created. This can be done by typing a measurement name in the bottom right input field, followed by pressing the Add button. In case you do not type in a measurement name at all, the default name Sample is used. As a result, a pop-up window appears, that contains a list of property values referring to the investigated sample, the environment, the applied impedance tube, auxiliary and geometry: 19

20 Sample: the name of the sample, the description of the sample, the manufacturer and the customer, the diameter and thickness of the sample in mm, the density of the sample in g/cm³, the gross density of the sample in g/cm³, the preparation/sealing and the surface/structure of the sample Environment: the environmental temperature in C, the atmospheric pressure in kpa, the relative atmospheric humidity in % Impedance tube: the diameter of the specific AFD AcoustiTube in mm, the length of the specific AFD AcoustiTube in mm, the shape and type of the specific AFD AcoustiTube Auxiliary: the operator and date of the measurement, possible notes Geometry: the distance z1 between the front of the material sample under test and the microphone one in mm, the distance z2 between the front of the material sample under test and the microphone two in mm, the distance z3 between the front of the material sample under test and the microphone three in mm, the distance z4 between the front of the material sample under test and the microphone four in mm The parameters referring to the environment show the values, that have already been defined in Setup. If the database option is activated, the sample parameters are to be chosen by selecting a certain sample out of the database using the "..." button (see Database). 20

21 By pressing the Ok button, the entries are confirmed and the measurement object appears in the measurement box above possessing the sample name typed in before. The measurement object possesses five child objects: Wave number, Sound velocity, Impedance, Propagation loss, Transmission and Transmission loss, representing the future result vectors of the measured complex wave number, sound velocity, complex impedance, propagation loss, sound transmission coefficient and transmission loss. The first measurement should be carried out with no material sample (air) to adjust the environmental temperature. The measurement can be started by selecting the measurement name with the left mouse button followed by pressing the Run button on the top left of the screen. If there is more than one existing measurement object and no measurement name is selected when pressing the Run button, a warning pop-up window appears. The progress of the measurement is depicted by the measurement bar. If the sound pressure level at the microphones gets to high, an Overload warning appears in red letters. By pressing the Stop button, the measurement can be finished before the number of averages is reached. To get precise measuring results, it is recommended not to do so. 21

22 The measuring results are shown below. Thereby, the absolute value of the complex wave number spectrum is chosen as default as shown in the legend right next to the diagram. The average measuring results of sound velocity and complex impedance should correspond to the common values for air 343 m/s and 408 Ns/m3 (valid at 20 C). If there are any differences in the measurement values, it is possible to adjust the environmental temperature by clicking with the right mouse button on the measurement name and modifying the specific entry in the Properties window). To check the adjustment, the formula sound velocity = 20,05 x temperature½ can be used. Please note to calculate with temperature values in [K]. 22

23 It is recomended to carry out the measurement without using the cutoff Algorithm at first (when use Cutoff under Setup is not checked). If there are switches in the measuring results (e. g. real part of complex wave number) like shown in the diagramm (see above), check the use Cutoff check box and enter a proper Cutoff. A good starting value may be 4. Furthermore, the Riemann frequency should be defined correctly. For measurements in the lower / upper frequency range of the transmission tube a value of approx. 300 Hz / 1000 Hz is appropriate. After the adjustment of the environmental temperature, an arbitrary material sample can investigated. It has to be taken care for placing the specimen in the specimen holder in an acoustically dense way. The following five figures contain typical measuring results of the several material parameters. 23

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26 After carrying out the measurement, there are various possibilities: By clicking on the plus symbols in front the measurement's child objects various sub-objects appear which represent different types of plots of the certain child type that can be shown. For example, it is possible to plot the 1/3-octave spectrum plot and the continuous spectrum plot (Cont.) of the transmission loss. Because the spectra of the wave number and the sound impedance are complex-valued, it can be chosen between the plots of the absolute value (Abs), the argument (Arg), the real part (Re) and the imaginary part (Im). Whether a certain plot is shown or not, is determined by the graph symbol in front of the specific plot type. By clicking on the graph symbol, the status of the plot type can be changed from "graph is not plotted" (empty graph symbol) to "graph is plotted" (graph symbol with plotted function) or vice versa. So, an arbitrary number of different plots can be shown at the same time. Also a combination of showing 1/3-octave spectra and continuous spectra is possible. With respect to a clear arrangement, the plot color can be adjusted by clicking with the right mouse button on the specific graph. The style of the frequency-axis can be changed from logarithmic scale to linear one by clicking the check box named by Linear Scale. Furthermore, it is possible to zoom into or out of the function by selecting a certain plot aera with a rectangular box. This can be done by clicking with the left mouse button into the diagram, holding the mouse button while moving the mouse and releasing the mouse button. By appointing the upper left corner of the rectangular before the lower right corner, the zoom-in function is carried out. By doing it vice versa or by double-clicking into the diagram, the zoom-out function is called. By clicking with the right mouse button into the diagram and holding it, the plot can also be shifted in an towards direction until the mouse button is released. By marking an arbitrary measurement object, the diagram properties are set to default again. 26

27 It is also possible to export the measuring result in ASCII-format. By clicking on the disc symbol in front of a chosen measurement's child object, a file dialog opens that requires the input of a file name. As default, a file name is taken consisting of the measurement object's name in combination with the child object's name plus an extension defining the file type. Thereby, it can be mostly chosen between exporting either continuous spectra (*.ct.txt) or 1/3-octave spectra (*.tf.txt). By using the Chart menu at the top of the screen, the depicted graphs can be exported in PNG-format. Existing measurement objects can be deleted by selecting the specific measurement object and pressing the Delete button. For safety reasons, a pop-up window opens, asking for the confirmation before this step is carried out. 27

28 By selecting a specific measurement object and pressing the Run button again, a measurement object can also be overwritten. Also here, a pop-up window opens for safety reasons, asking for the confirmation before this step is carried out. Using the Measurement menu, a measurement can be saved as *.xml-file. The same effect can be achieved by clicking on the disc symbol in front of the measurement name. If the database option is activated, the measurement is saved in the database instead. After that, the color of the disc symbol turns grey, indicating that the last changes of the measurement were saved. By using the Measurement menu, a measurement can also be loaded from *.xml-file or database again. By clicking with the right mouse button on the name of the measurement in the legend, the measurement properties can be altered. Changing the property values referring to the geometry or the environment and clicking Ok, a new calculation is carried out, which can be saved to a new result in the database. By changing the remaining properties and saving the measurement, the active result in the database is overwritten. 28

29 Postprocessing - Averaging of Multiple Measuring Results The next interface enables the averaging of multiple measuring results. This can be useful for determining a mean value representing the properties of a certain material. Depending on the measurements having been carried out so far, a list of measurement names with check boxes in front appear in the upper left interface box. Additionally, an Average object is created automatically, possessing the five child objects: Wave number, Sound velocity, Impedance, Propagation loss, Transmission and Transmission loss (compare to Measurement). Depending on the choice of measurements by activating the respective check boxes, the results are included to the averaging computation. 29

30 Referring to Measurement all described actions like showing multiple plots at the same time, zoom-in and zoom-out and so on can be carried out. Especially the possibility of exporting computation results in ASCII-format shall be pointed out. If the database option is activated the average result can be saved in the database by clicking on the disc symbol in front of the Average object. This requires, that all measurements included in the averaging computation have been saved. Choosing "Show Averages" in the Measurement menu, a list of the saved averaging data together with the respective measurements can be shown. 30

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32 Database - Reliable data management With the database option a list of materials and samples to be measured as well as lists of contacts of manufacturers and customers can be created. Measurement results are correspondingly saved and can be loaded again for quality control, comparison and statistical evaluation. The following depiction shows the structure of the database. A measurement object can be created by pressing the Add button on the right bottom of the screen as described in Measurement. 32

33 Apart from defining the tube geometry and the environmental conditions, property values of the sample can be defined or edited by clicking on the "..." button right next to the Name field. Another pop-up window appears showing a list of defined material samples. New entries can be added to the List of Samples, existing entries can be filtered, altered or deleted. The filtering allows to quickly find a requested sample. After selecting special critera from the list right next to the word "Filter" on the top left of the screen, an operator (=, <, >, like or ilike (ilike means, that the requested criterion can be entered without case sensitivity)) has to be chosen and the requested criterion has to be entered subsequently. The list entries are filtered by pressing the button Reload. By pressing the Add button, various property values can be defined: the material, the name of the sample, possible notes, the customer, the thickness and the diameter of the sample in mm. 33

34 By clicking on the "..." button right next to Customer, a List of Contacts is opened. 34

35 The existing entries can be also be filtered as described above to quickly find a requested one. The Add button allows the entry of new contacts. By pressing the "..." button on the right of property value Material, entries of the "List of Materials" can be added, edited or deleted. 35

36 It is possible to define the following property values: the name of the material, the density, the gross density of the material in g/cm³, the surface,density the manufacturer, a description of the material, the porosity of the material in %. Concerning the manufacturer, there is an extra button that opens a separate list that permits new entries and alterations as described above in the case of the customer. After confirmation of the entries or alterations by pressing Ok and the choice of a sample from the list, the measurement can be started by selecting a measurement object followed by pressing the Run button on the top left of the screen. By clicking on the disc symbol in front of the measurement name, the measurement is saved in the database. After that, the color of the disc symbol turns grey, indicating that the last changes of the measurement were saved (compare to Measurement). Using again the Measurement menu, already saved measurement data can be loaded, e.g. for comparison and postprocessing, by choosing "Load from Database". 36

37 The appearing list contains the available measurements with the following information: the Material, the Manufacturer, the Sample, the Customer, the Measurement Date, the Measurement Operator and the Measurement ID, the Result Date, the Result Operator and the Result ID. 37

38 Again, filtering of the available measurements is possible to quickly find the requested measurement. By choosing the special criteria and one of the operators followed by entering the requested criterion and pressing the button Reload on top right, the list entries are filtered. Please note: the Measurement date or the Result date need to be entered: Year-Month-Day, e.g the operators like and ilike do not work with date specifications Then the respective measurement can be selected. After having pressed Ok, the recorded data are shown in the measurement box of the fifth tab. For the various possibilities after having carried out a measurement please see Measurement and Postprocessing. By clicking with the right mouse button on the name of the measurement in the legend, the measurement properties can be altered. Changing the property values referring to the tube distances or the environment and clicking Ok, a new calculation is carried out, which can be saved to a new result in the database. By changing the remaining properties and saving the measurement, the active result in the database is overwritten. Average results from Postprocessing can be saved in the database by clicking on the disc symbol in front of the Average object. This requires, that all measurements included in the averaging computation have been saved. Choosing "Show Averages" in the Measurement menu, a list of the saved averaging data together with the respective measurements can be shown. 38

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