Visual Analyser HELPBy Alfredo Accattatis

Main window

Brief list of the functions implemented in Visual Analyser (VA)

VA is a real time program which simulates a set of electronic instruments, such as:

Oscilloscope (dual channel, xy, time division, trigger); Spectrum Analyzer with amplitude and phase display

(linear, log, lines, bar, octaves band analysis 1/3, 1/6, 1/9, 1/12, 1/24, CUSTOM spectrum);

Wave-form generator with "custom functions", triangular, square, sinusoidal (all with NO ALIASING and smooth transition), white(gauss, uniform)/pink noise, pulse generation, DC generation;

Frequency meter (in time and frequency domain) and counter; in time domain by means of a real time zero crossing algorithm;

Volt meter with DC, true RMS, peak to peak and mean display plus resolution calculus;

Filtering (low pass, hi pass, band pass, band reject, notch, "diode", DC removal);

Memo windows (data log) for analysis and storage of time series, spectrum and phase with "triggering" events; THD and Impedance data logging with spline interpolation; possibility to save the graphics in various format (.tee, .txt, .wmf) )and display them with an internal viewer;

Screenshot of Spectrum and Scope window; A TRUE software digital analogue conversion (for

complete signal reconstruction using Nyquist theorem) ; Frequency compensation: possibility to create/edit a

custom frequency response and add it to the spectrum analyzer computed spectrum; added standard weighting curves A,B,C in parallel with custom frequency response;

Support for 8/16/24 bit soundcard by means of API calls; Internal 80 bit IEEE floating point variables for minimum

rounding error; Unlimited frequency sampling (depend from the

capabilities of your soundcard/acquisition device); Cepstrum analysis; Cross Correlation; Extended THD measurements, with automatic sweep,

compensation, data log; ZRLC-meter with Vector Scope, sweep in time and

frequency for automatic measurement; original algorithm to reduce systematic errors,

Calibration mechanism (you can calibrate the VA scales directly in VOLT or dB or PERCENT FULL SCALE);

Set of values computed in real time (peak to peak, peak, crest factor, form factor, true rms, mean, frequency with zero-crossing algorithm);

..and more

About Visual Analyser (VA) and its author

(skip this section if you are interested only in the description of the main window and related functions)

I love electronics, and I have been working for years in commercial companies as software/firmware engineer and software designer. I've been writing programs for embedded systems (with DSP and MICROCONTROLLERS), for PC, for avionic computers and even for mainframes, using C, C++, Pascal, Ada and assembly. I write VA during my free time just for fun. The program is completely FREE.

Many people do not have the money to buy an expensive Oscilloscope or a Spectrum Analyser. Or simply they do not want to invest money for something they will use rarely. Nevertheless they love to build and test audio amplifiers or other kinds of simple circuits, and are only interested in the range of audio frequencies. So, a good soundcard could be all the hardware they need. A newer soundcard with a sampling frequency of 96 or even 192 kHz will allows to manage frequencies up to almost 100 kHz ( well beyond the audio frequencies) transforming VA in a powerful set of instruments for general electronics.

Latest versions of VA are able to manage also the 24 bit soundcard capabilities; if you are using a 16 bit soundcard, you'll be able the same to select the 24 bit modalities; in that case the resolution will be 16 bit shifted to the left of 8 bits (i.e. is the same to multiply the sample value for 256).

The idea of using the soundcard of a PC is not a new one (there are many of programs like VA) but I tried to write a program made for the analysis of audio circuits for the electronics hobbyist. I think VA is probably less "extravagant" than other (i.e. less windows and frills) but full of substance and even a lot of original idea.

General introduction

There are two ways of using VA. The "Standard" and "Floating" mode. The first time you run VA, after installation, it will run in "standard" mode. The VA.INI file does not exist yet (see warning at the end of this file), and so VA runs with default settings (i.e. in standard mode). If VA.INI is not present in the execution directory it will be automatically created.

Standard modeStandard mode means that VA is full-contained in a big main window of fixed minimum dimension of 790x637 pixel and freely sizeable over this minimum dimension. The main window contain the scope & spectrum windows plus a subset of the commands you can find

in settings window. Other commands and options are contained only in settings window, because less frequently used, although very powerful (example: the calibration function). The other windows (i.e. the frequency meter or the volt meter) are separate from the main window and in some case freely resizable. This separate windows will be visible only if the appropriate checkbox has been checked or the correspondent button (just under the caption of VA) pressed.

Floating modeFloating mode means that the main windows is reduced to a sort of command bar with a series of button, a "led" and a combobox for the selection of the input source (enabled only if the checkbox "apply calibration" in Setting/Calibrate has not been checked). In floating mode you can freely select the windows of your interest, in this way you can personalize VA according your needs. In floating mode all the windows are all freely sizeable (except the wave generator window and the setting window itself) and completely separate from the main window/command bar. In other words, if you, for example, need only a scope, simply press the button "scope", then resize the windows (full screen if you want...) and VA will be only a scope. Due to the automatic configuration saving, each time you run VA you'll find exactly the last configuration (see warning below). The scope and spectrum windows are provided of a "command bar" which contains some "shortcut" to

the commands most frequently used (auto-scale, average, logx/y etc.).

WARNING:The configuration of VA is automatically saved in a files named VA.INI, saved in the execution directory of VA (normally c:\programs\VA); this means that when you start VA, you'll find exactly the same configuration you left the last time at the end of the program. "Configuration" means the position and dimension of all the windows (except for settings window) and all the choice you made (ex. square wave in wave generator, A + B channels in spectrum/scope , trigger ON for left channel etc.). If you need to return at the default configuration you have two choice: (1) delete VA.INI (2) press the "default" button in Settings windows. If you need to save a particular configuration (to use at a later time for a particular purpose: for example determining the frequency response of your Hi-Fi amplifier), you can save the configuration in a different INI file pressing the button "save as" in Settings window and then defining a new name for the current INI file. To open this configuration file at a later time you should press the "Open config" button in Settings window and then select the desired INI file. Be careful that at the end of the program the new configuration will be saved in the current INI file, that is, the INI file indicated in the caption of VA or in the "info" windows.

The main window

The main window (standard mode) contains at a glance:

Oscilloscope; Separate main option for left and right channels; Spectrum Analyzer; Main commands, divided in sub folder (Main,

More, Cepst., THD, IMD); Pop-up menu for quick operation; Selection of input source; Slider for Input and Output level; Buttons for quick recall of main instruments; Input and Output gain button: to invoke quickly the

Windows mixer utility, both in case of Windows XP (and lower) and Vista/Seven

In more details the upper border of the main window contains the buttons (both in standard and floating mode) called COMMAND BAR:

On/off Setting Phase Scope Spectrum Wave Freq. meter Filters Floating Windows mode

Help

and the listbox for the selection of the input source, plus two slider for manage the input and output level. This listbox is directly related to the selected soundboard; when you select an input is exactly the same of selecting the input source by means of the Windows Volume control. You can invoke the original windows volume control opening the "Setting" window (click Settings button) and selecting the "calibrate" option. Then you need to press the "Windows volume" button. Warning: for some PC configuration with old or not properly installed mixer utility the input listbox may appear disabled. Use original windows volume control or install the updated driver for your soundcard. Some soundcard do not provide at all the internal input and/or output mixer and related software driver.

In the next section a detailed explanation of the button’s functions.

The COMMAND BAR

The ON buttons allows to start VA. VA is a real time program, it reads the samples directly form the selected soundboard by means of API calls. There are mainly three task. One read the samples from a buffer of selected dimension (a power of two, typical 4096 points) and store it in an internal dynamic buffer. After a read it will be suspended waiting for a new buffer.

You can select the dimension of the buffer selecting it in the "settings" window (see next sections). The more points you select the more resolution you get but conversely VA need more time to compute the Spectrum.

The second task get the dynamic buffer and compute the Spectrum by means of the well-known algorithm FFT (Fast Fourier Transform), and then plot it on the screen in the spectrum window together with the scope window.

The third task is completely dedicated to the user interface (buttons, listbox, etc.)

The OFF button is the opposite of the On button. In the latest version of VA it is the same ON button, that simply change its function, as standard for many Windows programs. Normally you can even change the settings of VA while it is running. The settings you can't modify during run will be disabled or may cause a temporary stop of VA (automatically).

The Settings button allows to invoke the settings window. This window allows to issue all the commands to VA plus the settings for the Soundcard and colors. You can use it for example when you're using VA in "floating mode"; in fact, the most common commands are directly available in the floating windows itself, but not all. So, if you need you can invoke the settings window, and put it in a preferred position on the screen

using it as a command-center. See help on setting window for further details (open the settings window and click the help button in the page you want help about).

The Scope button allows to invoke the floating scope window, allowing you to use the scope function. You can freely resize it up to the maximum screen resolution, using VA as it were only a scope. Or you can use it together with other windows (for example the frequency meter window or the spectrum window). A useful sub menu will appear in the scope window by clicking the right mouse button. The Scope button will appear disabled if the Standard mode is selected. See scope window help for further details about the scope window (open scope window, right mouse click and select the help item).

The Spectrum button allows to invoke the floating spectrum windows; this button will be disabled (it do not appear at all) when the standard mode is selected. The spectrum window, as the scope window, allows you to freely resize the dimension up to the maximum screen resolution; also for this window a quick menu will be available by clicking the right mouse button; in that menu you can select the help button for further details about the floating spectrum window. See also the help related to the Setting/Spectrum window.

The Phase button, allows to invoke the phase window. This is a window not normally displayed during the

standard mode use of VA, i.e. not directly visible in the main window of VA. This window allows to visualize the phase of the signal(s) currently displayed in the spectrum and scope window. The phase will be normally visualized in degree, and you may want visualize it together with the spectrum window. The X scale is the same of the X scale for spectrum window, allowing you to tile the two windows for visualizing a complete "bode diagram". Also this window is freely resizeable, allowing you to resize up to the maximum screen resolution. A quick menu is available by right clicking the mouse, with an help item to get further details about the phase window itself. NOTE: this window is intended to be still a beta version. No valid feedback for now...

The Wave button allows to invoke the wave generator window; this is one of the most powerful function of VA. It cannot be freely resized, and can be closed while running without affecting the selected function ; the "on" button can be invoked directly from the main window, for simplicity of use. That is, you can invoke the wave window, select the function of interest, then close the wave window and subsequently start/stop the wave generation from the main window (by clicking the on button between the "capture scope" button and the "wave gen" checkbox). This will not be possible if you are in floating windows mode, altought you can still close the window without stopping the function generation (if on selected). See the help included in the window itself for further details.

The Freq. Meter button allows to invoke the frequency meter window. This is a window not normally displayed during the standard mode use of VA, i.e. not directly visible in the main window of VA. This window allows to detect the frequency of the harmonic with the maximun amplitude in the whole spectrum of the input signal, as a true frequency meter. This window starts a new dedicated thread; the red flashing indicator in the upper left corner of the window indicate the moment in which frequency meter is reading data from the spectrum; the frequency will be computed between two red flashing. Click the help button in frequency meter window for further details about the frequency meter.

The Filter button allows to invoke the settings window, opening directly the subsection "filters". See help on settings window for further details.

The Floating windows mode / Standard mode button allows to switch between the two modalities "floating" and "standard". Normally, the default mode for VA is "standard mode", that is, the button will indicate "Floating windows mode"; conversely, after the switch in floating windows mode the button will indicate "Standard mode".

The Help button will invoke this text.

The listbox “Input selection” allows to select the input

source. The behaviour of this control is different according to the operating system. In fact, using XP the meaning is “selecting the input of the selected input board”. This latter can be selected in the Setting window, in the Device TAB. On the contrary, Windows Vista/Seven does not allow to select a device and of that device a particular input; Instead, Seven allow to select only an Input, independently from the actual device who is “hosting” the input. So, when VA run under an operating system from Vista on, the meaning of the input listbox is the same all over the program (hence, also in the setting window): input source.

The trackbar “Input level” allows to modify the input sensivity of the selected input source; for maximum generality, the scale is calibrated from 0 to 100.

The trackbar “Output level” allows to modify the Output level of the selected output source; for maximum generality, the scale is calibrated from 0 to 100.

Due to the large number of instruments implemented in VA, in many section and window of VA there are slider (trackbar) similar (identical) to the “Input Level” and “Output level” main slider, present in main window. This is for practical reasons; and fully synchronised each other. For example, one can find the same trackbar of the Input Level (present in main window) in the Settings/Calibrate window, simplifying the calibration procedure itself (if one need to change the

input sensivity, it is not necessary to switch between two windows); in addition, in calibrate window the Input Level trackbar has been duplicate, allowing to manage separately the two channels (left and right) allowing, as further option, a complete indipendent calibration for the two channels.

The remaining options can be divided into two main groups: the “spectrum options”, to the right of the spectrum window, and the “oscilloscope options”, to the right of the oscilloscope window. The spectrum options contains also some setting of the oscilloscope.

Spectrum options

that options are subdivided into four main groups:

1)Main2)More3)Cepstrum4)THD5)Uncert

(1) - Main tab

This important group of options comprises the main setting for the spectrum analyzer. They are reported also in the setting window, and here repeated for commodity when necessary; see Setting/Spectrum help for further information.

Y-axis group: in this group it is possible to set the most important feature of the Y axis of the Spectrum Analyzer instrument. In particular the trackbar allows to set the “zoom” scale factor; the button “auto” allows to set automatically the zoom scale factor, finding the maximum and minimum value of the spectrum amplitude and adjusting the zoom trying to fit the spectrum entirely in the window. The “Log” checkbox allow to switch from the linear representation to the logarithmic representation. This latter is obtained plotting the ordinate in dB relative. The value considered as zero dB can be adjusted manually by

clicking on the scale with the right mouse button and selecting “Zero Adjust” option from the popup menu (Zero Adjust, Reset zero, Auto : see below); then, the zero value can be modified by dragging with the mouse cursor holding down the left mouse button. In this case the color of the scale will flash between a blue color and the standard color selected for the channel. After finishing with the operation, it is necessary to recall another time the pop-up menu and de-select the “Zero Adjust” option.The popup menu contains three options, quickly explained below.Zero Adjust: enable/disable the Zero adjusting by mouseReset Zero: set the zero at the default value (=maximum allowed from the resolution)Auto: set automatically the zero level as the harmonic of maximum amplitudeThe same option are available in the Setting/Spectrum tab of the setting window.

The “Hold” checkbox activate a function that allows to maintain only the maximum value reached by the spectrum (peak hold) for each point of the graphic; that is, for each frequency is plotted the higher amplitude continously from the moment of the activation on. After a long time interval the graphic will be most probabily a static curve unless new peak is detected.

The “Lines” option allow to switch (when expected) between the “bar” representation and “line”

representation. This latter kind of plot is obtained simply joining the points with a segment (no interpolation).

The “Info” option activate a further set of information immediately below the frequency indicator in spectrum analyzer window, at the upper left corner. The “frequency indicator” show the frequency of the harmonic selected by mouse when left mouse button is hold down and the mouse moved on the spectrum: with this latter function it is possible to display in a special window, locked near the mouse cursor the list of all the harmonic represented in that particular pixel with amplitude, frequency and units. Moreover, in the upper left corner is displayed the frequency of the first harmonic of the list, and if the info option checked also the amplitude in dB relative.

The “average” listbox allows to select among a series of possible average factors, from 1 to 200 (and shortly will be added the “infinite” option). The operating principle is simple and powerful; the average is computed on the last “n” buffer, with n varying, as said, from 1 to 200. The average operate in a modalities “first-in, last-out”, meaning that the average is computed on the latest “n” buffer, that is, for instance, if n = 10 this mean that after the available buffer are > 10 each new buffer is added at the tail of the queue and the buffer at the head of the queue discarded. In this way are maintained only the latest 10 buffers, and the average is computed exclusively on them.

The “Step” option allows simply to define the “step” of the vertical division in dB or Volt when allowed.

X-axis group: in this group it is possible to set the most important feature of the X axis of the Spectrum Analyzer instrument. The “log” checkbox allows to change the representation from linear to logarithmic of the X axis; the “3D” option allows to activate a special modality (waterfall) enabled on almost all the standard representation of the spectrum. It is still beta and under construction (2011 version).The “true X” checkbox allows to switch between two different modalities to round the written numbers; when selected, means that the values plotted on the scale are exactly the values that the pixel represent; otherwise it is a rounded value.The combobox below the “true X” option allows to select among the following option:

Fitscreen x1 x2 x4 x8 x16 Octaves CUSTOM

The “Fitscreen” option allows to plot the spectrum with

ALL the information available, adapting the plot to the visible screen. This according to the following rules.VA compute the harmonics according to the number of points of the input buffer actually available (i.e. the half of the dimension of the input buffer); and taking into account that, as stated before, the number of pixel of the X-axis is general different from the points to be plotted. For example, having a window with 512 pixel:

1 pixel = 1 harmonic if the number of harmonics is 512 (buffer of 1024 points), the spectrum can be plotted simply linking two consecutive points with a line;

1 pixel = two harmonics if the number of harmonics is 1024 (buffer of 1024x2 = 2048 points); this means that in some way VA must use only one pixel for two points;

1 pixel = representative of three harmonics if the number of harmonics is 2048 (buffer of 2048x2 = 4096 points)

...and so on..

if the number is less than 512: 2 pixel = 1 harmonic if the number of harmonics is

256 (buffer of 256x2 =512 points) 4 pixel = 1 harmonic if the number of harmonics is

128 (buffer of 128x2 =256 points) ...and so on..

The general rule of VA is: DO NOT LOST or CONFUSE harmonics. Apparently it is not possible to

display more harmonics than the number of pixel actually available; nevertheless VA is able to do this without lost a single bit of information. Having “n” pixel with “m” harmonic (m greater than “n”) the trick is to display precisely more than one harmonic with a single pixel. NOT by summing the harmonics or (even worse) calculate the average value or simply by displaying only the harmonic with the higher level (this latter possibility is indeed allowed only if desired, by selecting an appropriate option in the “more” TAB of the main option described far below).

The trick is to plot all the harmonics and hence obtaining a vertical line giving the idea that the pixel is representative of more than one harmonic; moreover, you can distinguish exactly amplitude and frequency of each harmonic by means of the mouse and a special window: simply by clicking with the left button over the desired harmonic (holding the button pressed). A special window appear “locked” near the mouse cursor, displaying the list of ALL the harmonics “contained” (frequency and amplitude) in that point.

The “x1..x16” options are exactly the opposite of the fitscreen. In fact, simply means that the harmonic are plotted each “n” pixel, where n vary from 1 to 16. For example, if we select n = 4 (x4) this means that the harmonics will be plotted each for pixel; if we select x1 we obtain 1pixel=1harmonic and so on. In this way probably the complete spectrum does not fit the available window (as number of pixel) and a trackbar

will appear at the bottom of the spectrum window allowing to “navigate” horizontally in the spectrum amplitude.

The “Octaves” option allows to plot the spectrum in Octaves, enabling the combobox the allows to select among 1, 1/3, 1/6, 1/9, 1/12 and 1/24 of octave.

The “CUSTOM” spectrum should be not confused with Octaves representation, although similar at first look. It allow in fact to define a spectrum arbitrarily, with the value of the computed harmonic NOT obliged by the frequency sampling and buffer length pair. In fact normally, the computed harmonics are at a predefined frequency distance, determined by the step computed as :

Step = (frequency sampling) / (buffer dimension)

For instance, for a frequency sampling of 40960 Hz and a buffer dimension of 4096 points we get: Step = 40960/4096 = 10 Hz. That is the first computed harmonic is 10 Hz, the second 20Hz, the third 30Hz and so on up to 40960/2 = 20480 Hz. Using the CUSTOM option it is possible to define up to 1000 harmonic at ARBITRARY frequency. To define (and save) the list of desired frequency, you should open the definition window in Setting window and Spectrum tab (Setting/Spectrum) by means of the button “Custom”. See help in the window itself for the explanation of the definition process.

Channel(s):

Channel(s) combobox allows the selection of the channel to be plotted on almost all the windows of VA. The indicated colors are referred to the default; “A” channel is to be intended the left channel and “B” as the right channel if a soundcard is used.

Ch A: (green color) select the left channel of the acquisition device. The oscilloscope will display only the left channel, the same for the spectrum, for the volt-meter and the frequency-meter. The window of "Capture spectrum" and "Capture scope" functions will be filled only with left channel samples.

Ch B: (red color) The same of Ch A but changing left with right.

Ch A and B: (green and red color) By selecting this option you will be able to view both the left and right channel on the scope window and the spectrum window. The frequency meter will show the left channel frequency while the voltmeter both.

Ch A/B (B/A): This is a special modality that allows to display the transfer function of a device if properly connected. Normally used to compute the frequency response of an audio device. In

particular the A(B) input channel should be connected to the input of the device under test (DUT) and the B(A) channel should be connected to the output of the DUT. The program will compute the transfer function of the device by calculating the difference in dB of the two channel (A-B or B-A, that using dB units is equivalent to compute the ratio A/B or B/A) or directly the ratio if linear scale used. The voltmeter will display both the channel and the frequency meter only the left channel.

Ch A - B: The displayed spectrum is the spectrum of the difference of the channel. DO NOT CONFUSE with the transfer function option; in fact in this case the two channel are subtracted before the FFT, in the time domain. In this way, the signal is a single one and treated as a standard channel.

Ch B - A: The same of the previous point with the channel swapped

X Y: This is an x-y visualization as a true oscilloscope. The X-axis is the LEFT channel, the Y-axis is the RIGHT channel. The spectrum analyser windows will show both the channels, as the volt-meter. The frequency meter will show the left channel.

Ch A + B: Selecting the Ch A + B item the scope windows will show the sum of the two channel (yellow color), as the spectrum window, the volt meter windows and the frequency meter window.

Ch A cross B: The signal displayed by the

spectrum analyzer window is the spectrum of the cross-correlation between the A and B channel (left and right); the signal displayed by the scope window is the correlation signal.

Ch B cross A: The same of the previous point with the channel swapped.

Wait, Req., Used indication. The “numbers” plotted in this little windows, are the core of the acquisition process of VA and very important indicator of the correct running of the data acquisition thread. “Req.” stand for “Requested” and is the time requested to get two consecutive buffers of data. If we select a buffer dimension of 4096 point, at the frequency sampling of 40960 Hz, the time to get two consecutive buffers is 4096/40960 = 0.1 seconds, that is 100mS. Naturally during this time VA has a buffer available and, waiting for the next, can in the meantime implement all the necessary computation to implement all the activated instruments (for example compute the FFT and manage the user interface). The “Used” indication is in fact the time actually used by VA to do the jobs, while the “Wait” is the difference between the actually used time and the “Req” time, that is the time NOT USED from VA. When the time not used from VA is higher than zero, and this means that VA is running on a PC with a sufficient number of resource to execute the job, the “wait” written remains gray, otherwise it became RED. In this latter case means that VA is overloading the processor.

Capture Scope: this button allows to activate one of the most important function of VA; the so called time domain capture function. It allows to “capture” in a separate window all the acquired from the time the button was pressed (and compute spectrum, save on file, explore, convert from digital to analogue, etc). See the help in Capture scope itself for further details, and the Setting/capture window help for the capture main option.

Capture Spectrum: this button allows, as the previous described function, to capture directly the computed spectrum of the spectrum analyzer in a separate window. See the help in Capture scope itself for further details, and the Setting/capture window help for the capture main option.

“WaveOn” : this is a shortcut to the On/Off button of the waveform generator; it allows also to distinguish if the function generator is running in “loop” modality or not. In fact, when in loop modality, after activating the generator the caption of the button will switch from “WaveOn” to “WaveOff”. If not in loop mode, it again will switch but the caption will flash according to each buffer passed to the acquisition/generator board. In other words, if the real time mechanism of waveform generation has been used, the caption will flash each time a new buffer is passed to the hardware.

The “Info” button allows to open a simple window with

the main parameters listed in a table.

A group of checkbox, listed below, allows to invoke all the instruments implemented in VA; except the first, conceived to switch on/off the “stay on top” attribute of the VA window, according to user needs. The complete list of the checkbox:

1. Stay on Top2. VoltMeter3. Freq. Meter4. Wave Gen.5. Phase6. THD view7. THD+noise view8. ZRLC meter

(1) Has been already described;(2) The frequency meter window appear;(3) The Waveform generator window appear;(4) The Phase window appear;(5) Allows to enable the automatic THD (Total

Harmonic Distortion) calculus using the harmonic with maximum amplitude taken as start point. The results are displayed on the Spectrum Analyzer window, with the same color of the activated channel (displayed at the upper left border);

(6) The same of (5) but for THD plus noise calculus;

(7) The ZRLC window appear; this function require a simple hardware to be connected to the dual channel

acquisition board or soundcard; an example is reported in VA, see Setting/ZRLC window, checkbox “Sch”, or see www.sillanumsoft.org <http://www.sillanumsoft.org> ZRLC section.

(1) - More tab

More stands in this case for “more option” and historically born when VA needed to manage more options than the standard options present in “main tab”. They are related to Spectrum Analyzer and Oscilloscope function, plus a viewer for the data saved in standard Capture functions and ZRLC capture. It includes a lot of new powerful options as the “frequency compensation”, the definition of the X axis extent, the screenshot and uncertainty. Moreover there is the possibility to change the “philosophy” of plotting modality for spectrum and scope (point/pix options).

Log viewers: the capture function, both in time domain and in frequency domain, offer the possibility to save the acquired data in many way (i.e. as text, in clipboard and in .tee format). Saving the graph in .tee format is the preferred method, allowing to save all the information of the graphics (including color, number of graphics, titles etc). To plot real time all over the program have been used proprietary routines, except in the capture window, where has been used the

TeeChart standard (see www.steema.com <http://www.steema.com>) shipped with the compiler used to develop VA. This graphic Class allows to save the graphics in a standard format with .tee extension. VA used to add some extra data to distinguish between the type of data saved (Spectrum, Time series, THD etc all in common .tee format but related ad different kind of data) and allowing to optimize the process of backup and off-line analysis. In other words, you can save the data and re-open it at any time using the “Open Graph” button, without care if data has been saved from ZRLC/THD or Capture Scope or Capture Spectrum or whatever. In case the data were saved with an older version of VA, it is possible to select the “Manual” option allowing to select manually the type of graphic to be loaded (buttons “Scope”, “Spectrum”, “Thd/ZRLC”).

Points/pix: this first group of option, located approximately to the left below the Log Viewer group, is related to the Spectrum Analyzer. It allows to select one of the following three options:

Full Single MinMax

“Full” means that the graphics, when (and only) the option “Fitscreen” selected, is plotted as described for the fitscreen option (described in detail elsewhere in this help). As reminder, the fitscreen modality implies

thet in some cases more than one harmonic is plotted for each pixel of the screen. If instead the “Single” option is selected, only one harmonic of the group of the harmonic represented by the pixel is actually plotted: in particular ONLY the one with the higher amplitude. In this way the Spectrum will be plotted in the fastest way. In fact, sometime, due to the large number of harmonics to be plotted with a limited number of pixel, in a single pixel the graphic routine must iterate a lot of times to plot all the associated harmonics. Getting nothing more than a vertical segment. By selecting the “single” option will be plotted only a single pixel (related to the maximum amplitude harmonic) and only one time.

In other words, the key difference between Full and Single is that with the Full method the graphic will be composed (also) of a lot of vertical line (similar to bars) in correspondence of multiple harmonics per pixel; in “single” the graphic will be composed ONLY of a set of consecutives line linking single pixels.

The third option (MinMax) allows to plot a graphics identical to “Full” but plotting exclusively the harmonic of the multiple group having the minimum and maximum amplitude. Obtaining in such way (a) resource saving (b) same information and appearence of “Full”. It should be the preferred method for Spectrum graphic with a lot of harmonics and a logarithmic scale selected for X-axis.

Points/pix: the second similar group, located at the lower right corner of the “more” option tab, has the same meaning of that of the Spectrum, but related to the Oscilloscope instrument. In this case the “single” option is NOT present as nonsense for an oscilloscope (time domain and with sign).

X Freq Range group: exploiting this option it is possible to define arbitrarily the range of the X axis; the automatic modality allows to select the automatically the maximum range allowed from the choosen sampling frequency. Two preset button are present as further facility.

Screenshot: the screenshot group contains a button to capture an hardcopy (bitmap) of the Spectrum window and of the Scope window. The third button allows to invoke a simple bitmap viewer; in the open file window a preview of the selected file is available.

(3) - Cepstrum

TBD

(4) - THD

TBD

(5) - Uncert

“Statistical (A) uncertainty SPECTRUM” Group: allows to choose the value of an harmonic and to select if compute the uncertainty of A-type (statistical) for Spectrum Analyzer. The selection of the checkbox “Spectrum” will invoke the uncertainty window estimator, described in detail in local help. Note that the A-uncertainty estimator work in a separate thread and in real time. At the moment of writing this help, the uncertainty estimator windows works only for left (A) channel, or right channel (B). When both channel are selected, only the left channel uncertainty will be computed. The “enable” checkbox allows to invoke the uncertainty window. Note that the list of available harmonic will be updated if “custom spectrum” or “standard spectrum” selected. The uncertainty may be computed on the amplitude or phase spectrum.

“Statistical (A) uncertainty SCOPE” Group: The selection of the checkbox “Scope” will invoke the uncertainty window estimator, described in detail in the proper local help. Note that the A-uncertainty estimator work in a separate thread and in real time. At the moment of writing this help, the uncertainty estimator windows works only for left (A) channel, or right channel (B). When both channel are selected, only the left channel uncertainty will be computed. The uncertainty may be computed on true RMS value, MEAN value (both computed only on one input buffer) or directly on the input sample (ALL points option). In this latter case the number of samples will be very

high, and then the uncertainty estimator window maximum number of samples reached quickly. In fact, if true rms or mean value is selected, for each input buffer a single measurement is performed, and then a single sample sent to the uncertainty window. If “all points” option selected, all the points in the input buffer are sent as separate measurements. For example, for a 4096 buffer points, choosing a “true rms” uncertainty calculation, a single value is sent to the uncertainty windows each 4096 samples. Choosing “all points”, 4096 different values are sent to the uncertainty windows. The safety limit of internal points memorization of the uncertainty window is one million points. After this value the histogram will not be updated anymore while the uncertainty calculus, mean and standard deviation will continue indefinitely to be updated.

Scope options

The option of the oscilloscope instrument are located to the right of the scope window itself; they are replicated in the setting window. The setting window contains further options. Each channel has its own separate options, although exactly the same. Indeed the right channel group has one more option (“trig left” checkbox) allowing to trigger the left channel by means of the right channel parameters (see next sections for further details). The following controls description must

be intended for both channels except when explicitly declared.

The scope window has two vertical scale that, as explained elsewhere in this text and in other help files, can be calibrated in percent full scale (%FS) and/or Volt. As for the spectrum analyzer window, the vertical scale could be enabled or disabled, accordingly with the channel selection. The background color of the scale is the same color chosen for the channel (that is, the same of the graphic color).

Vpos vertical trackbar. Vpos stands for “Vertical position” and allows to vary the vertical position of the graphic track (of the related channel), varying correspondently the associated vertical scale.

Trig vertical trackbar. Allows to vary the trigger level, when (and only) the “Trig” checkbox is enabled. It allows to display graphically the desired trigger level by means of a dotted line of the same color associated to the channel (i.e. if the channel color track is red, the color of the dotted line will be red). The trigger level has actually two meanings; the first is the standard one, that is “the level of trigger used by the internal algorithms to trigger the waveform displayed from the oscilloscope instrument”; the second is related to the “Capture” in the domain time (i.e. the Capture scope function, see elsewhere in this text and the local help of setting/Capture window). In this case, the trigger represents (also) the threshold of the capture scope

function, when the proper option has been enabled in the setting/capture window (“after crossing trigger threshold” or “only samples > trigger threshold” option selected). Also if used for this second purpose, the trigger functionality will not be disabled (that is, the trigger will acts anyway).

ms/d stands for “millisecond/division” and is the equivalent of time base of a standard oscilloscope.

The oscilloscope time division is computed keeping in mind the base concept already used for Spectrum Analyzer instrument (and for the whole set of instruments implemented by VA) : do not loss or mess a single bit of acquired data.

Due to the VA philosophy the time division value depends also from the dimensions of the oscilloscope screen dimension, and so it will vary if the window of VA resize. In other words, if you set a value of, say, 2 mS, and the window is resized, the time division could be automatically modified (it become lower if the window horizontal dimension decreases, and vice versa). The time division displayed by the control is the time between two adjacent vertical line, and it depends from the number of pixel between the two vertical line. Varying the dimension of the window, as the number of horizontal division will remain the same, the distance between two adjacent line will vary correspondently. In fact, as for each pixel is associated a “quantum of time”, the time division will vary necessarily.

The idea behind the time division mechanism is as follows.

The default time division setting (that you can set quickly by clicking on the “zero button”, the small button at the upper left corner of the ms/d edit box) mean that for each pixel a single sample is plotted. The internal value of time division variable is in this case equal to 1 (one). By clicking the “up” button of the “updown control” (at the right of the ms/d edit box) it will be incremented by one; on the contrary decremented by the same quantity. For positive values the meaning is “the number of samples plotted for pixel”. So, as we know the distance in pixel from two adjacent vertical bars (“dist” variable), and the frequency sampling (“freq_sampling” variable), it is easy to compute the value of time division, by means of the following formula:

Displayed time division in mS = ( 1 / freq_sampling ) * dist * 1000 * num

Where the “num” variable is a positive number

When the “num” variable is negative, the meaning is “number of samples plotted each “num” pixel. For instance, if num==-5 means that two adjacent samples will be plotted each five pixel (and connected by a line segment). The displayed time division will be computed in this case by means of the formula:

Displayed time division in mS = ( 1 / freq_sampling ) * dist * 1000 / abs(num)

To modify the number of both horizontal and vertical division of the Oscilloscope window, one should use the options located in the setting/scope window; in particular see the “Scope grid” groupbox, and give a look to the local help.Zoom control allows to zoom the Y axis of the oscilloscope instrument; it simply multiply the samples for a zoom factor (the integer number defined in the zoom edit box). The zoom factor can be varied from 1 to 256, and the corresponding Y-scale modified accordingly.

Trig checkbox allow to enable/disable the trigger function; it enables/disables the corresponding trackbar controls.

Inv checkbox simply invert the sign of the corresponding channel when checked.

Trigger groupbox. Allows to define the main parameters of the trigger function; in particular, the slope of the wave form which the trigger should occur ( positive, negative ) and the threshold factor, expressed in a scale from 1 to 1000 (i.e. expressed in a “per Thousand” scale) . So, the trigger level threshold will be considered reached by the input signal if the value of the current sample is within a range computed

as follow:

Trigger interval = [ TrigLev, TrigLev + MaxAmplitude * ThFact ]

Where TrigLev is defined by means of the Trigger trackbar and graphically displayed on the oscilloscope screen; MaxAmplitude is the Maximum amplitude of the input signals (in internal units, i.e. if the resolution is 16 bit the maximum amplitude is 216 varying from -32768 to 32767) and ThFact is the Threshold in per Thousand of the MaxAmplitude. Also TrigLev has to be considered as having the same unit of MaxAmplitude.

The threshold parameter is useful because of the different nature of the input waveform and related edge. In general with a very steep edge will be recommended a higher value of Threshold, conversely with a smooth waveform edge will be recommended a lower one. In any case it should be determined experimentally from case to case. Leave to the default value for most practical cases.

D/A checkbox. D/A stands for “Digital to Analogue conversion option”. It is one of the most important option of VA; in fact, there are a couple of threads dedicated to that function.In standard use, without the D/A option checked, the samples are plotted on the screen simply linking them with a line; that is, no interpolation routines are used. This is a common way to display data in program

similar to VA. For most practical case it is the fastest and practical way to implement a digital oscilloscope; but, as we will see in the next lines, it is not practically useable under certain condition. Let’s do a little preamble.

The acquired samples must be acquired under the Nyquist theorem conditions. That is, the frequency sampling must be at least double the maximum harmonic component of the input signal. To avoid problems, normally before the A/D conversion a filter called anti-aliasing filter is used to limit the band of the input signal according the frequency sampling. In that way we are sure that the acquired samples are meaningful and aliasing do not occur. In other words, using the sampling process under the Nyquist theorem condition, we are assured to get a digital sequence that represent completely the original signal without any loss.

However, this signal, stored in RAM and used by all the instruments implemented from VA it is NOT the original analogue signal, although mathematically equivalent; it is composed only of a discrete sequence of samples (that is, a sequence of values of the signal captured at predefined time instant). Problems could arise trying to plot the signal on the oscilloscope screen, as VA try to plot an analogue signal by means of a numeric one. As already said previously, the signal is plotted on the screen simply linking two consecutives digital samples by means of a line. When the sampling frequency is

considerably higher than the frequency of the input signal, the result on screen is almost indistinguishable from the analogue signal; on the contrary, when the frequency sampling is comparable to the signal frequency, the result is (apparently) a signal completely different from the original. For example, if we try to plot a sinusoidal signal at 1000 Hz sampled ad 2000 Hz, we would get only two samples for a single sinusoidal cycle; although sufficient to rebuild mathematically the original analogue signal, the plotted signal obtained with the simple “line linking” technique will be similar to a triangular-trapezoidal wave form instead of a sinusoid.

So it is necessary to rebuild the original signal applying another time (and in reverse manner) the sampling theorem (Nyquist). Or, in other words, implementing via software a complete Digital to Analogue converter.

For this purpose, VA implement a signal reconstruction applying the Nyquist theorem; enabled only when “D/A” checkbox is checked. A new thread is instantiated to compute the original analogue signal in real time. Naturally, approximations has been made due to the limited number of samples available during the real time computation.

The D/A thread is resource consuming, and then to avoid useless waste of resources, an automatic routine determines, by checking the frequency sampling, buffer dimension and requested time division, if the D/A

routine have to be actually enabled. In other words, also if D/A has been checked the D/A thread will not be actually executed if the standard displayed signal (with raw line-link) is undistinguishable from the reconstructed one.

DCremoval checkbox allows to insert along the flow of the input signal a digital filter to eliminate the DC component. It is a simple IIR high pass filter with the cut off frequency set to 0.01 Hz.

Trig Left is an often misunderstood option that allows to trigger the left (A) channel by means of the parameters of the right (B) channel and its input signal. In other words, the trigger mechanism of the right channel acts on the waveform actually read from the right input, and in contemporary the same computed trigger point is applied to the left channel.

In general when the desired trigger level (and with the desired trigger threshold) is reached the right channel is triggered simply starting to plot the right channel from the point which fall in the trigger interval (this is a general mechanism, true for both channels). The difference, using “Trig Left” option is that the same trigger point is applied also to the left channel, independently from the waveform actually measured. Allowing a functionality similar to the “external trigger” of a standard oscilloscope.