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university:tools:m1k:alice:oscilloscope-x-y-user-guide [25 Jun 2021 19:52] – [The Top Menu Section] Doug Mercer | university:tools:m1k:alice:oscilloscope-x-y-user-guide [17 Jan 2023 20:03] (current) – add cautionary note Doug Mercer | ||
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Press the <alt> and < | Press the <alt> and < | ||
- | It is possible to save the graphics display area to an encapsulated postscript file (.eps). This is used to save a graphics file to be included in another program like a word processor to write a Lab report. It is also possible to save the captured channel A and B voltage and current signal data to a coma separated values file (.csv). For most Time/Div settings the number of sample points is 2 screen widths with a minimum of 2,000 samples and a maximum of 90,000. This saved table of raw sample values can then be loaded into other programs for analysis such as a spreadsheet program or numerical processing program like MATLAB, | + | It is possible to save the graphics display area to an encapsulated postscript file (.eps). This is used to save a graphics file to be included in another program like a word processor to write a Lab report. |
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+ | It is also possible to save (with Save To CSV button) | ||
The Options drop down menu, figure 2, lists a command for enabling smoothing where spline curves are used to connect the input sample points rather than the default straight lines. A second option for connecting the sample points is to use a zero order hold function where a horizontal line and a vertical line are used. This looks like a stair step waveform much like the output of the Digital-to-Analog converters used to generate the AWG output signals actually produce. | The Options drop down menu, figure 2, lists a command for enabling smoothing where spline curves are used to connect the input sample points rather than the default straight lines. A second option for connecting the sample points is to use a zero order hold function where a horizontal line and a vertical line are used. This looks like a stair step waveform much like the output of the Digital-to-Analog converters used to generate the AWG output signals actually produce. | ||
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<WRAP centeralign> | <WRAP centeralign> | ||
- | The Trace Avg button turns on trace averaging. The number of sweeps to average can be set with the Num Avg button. The width of the traces in pixels can be set with the Trace Width button. | + | The Trace Avg button turns on trace averaging. The number of sweeps to average can be set from the Change Settings controls |
The currently displayed traces will be saved via the Snap-Shot option as reference traces. They can be added to the graphics plot area by selecting the desired trace from the Curves drop down menu for time plots. They will be drawn in a darker color corresponding to the matching live waveform trace. | The currently displayed traces will be saved via the Snap-Shot option as reference traces. They can be added to the graphics plot area by selecting the desired trace from the Curves drop down menu for time plots. They will be drawn in a darker color corresponding to the matching live waveform trace. | ||
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To keep production costs of the board low, certain trade offs were made. One was to forego programmable input gain ranges that use resistor dividers and perhaps adjustable frequency compensation capacitors. This limited the usable input voltage range to 0 to +5V. | To keep production costs of the board low, certain trade offs were made. One was to forego programmable input gain ranges that use resistor dividers and perhaps adjustable frequency compensation capacitors. This limited the usable input voltage range to 0 to +5V. | ||
- | At the bottom of this section, just above the ADI logo, are entry windows which allow input gain and offset adjustments or corrections for any external resistor divider attenuator networks that might be added to the channel A and B inputs ( possibly used when in the high impedance or Split I/O modes ). Save and Load Adj buttons can be found under the File drop down menu. | + | At the bottom of this section, just above the ADI logo, are entry windows which allow input gain and offset adjustments or corrections for any external resistor divider attenuator networks that might be added to the channel A and B inputs ( possibly used when in the high impedance or Split I/O modes ). Save and Load Adj buttons can be found under the File drop down menu. |
- | The input capacitance, | + | ===Input Divider Calculator=== |
- | A capacitor would generally be needed across the input resistor R< | + | To make calculating an input resistor divider' |
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+ | {{ : | ||
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+ | <WRAP centeralign> | ||
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+ | Values for resistor R1 and resistor R2 are entered as well as any offset voltage that is applied to the bottom of the divider. The Exact values, as measured with a bench DMM, can be entered for R1 and R2 to calculate more accurate gain and offset results. The Rint internal 1 MegΩ resistance of the channels is taken into account in the calculation as this will have a significant effect for higher values of R1 and R2. Click the Calculate button to calculate the values. The Channel A or B entries can then be set to the calculated values using the Set CH A and Set CH B buttons respectively. These values can then of course be tweaked as needed for even better accuracy. | ||
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+ | === Software Frequency Compensation=== | ||
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+ | The input capacitance, | ||
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+ | < | ||
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+ | To give you a rough idea let's use 400 pF for C< | ||
{{ : | {{ : | ||
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The software frequency compensation for each channel consists of a cascade of two adjustable | The software frequency compensation for each channel consists of a cascade of two adjustable | ||
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+ | <note tip> | ||
+ | **Exponential compensation**\\ | ||
+ | An Exponential compensation technique adds one or more exponentially decaying terms to a step in the signal. With 2 available stages, ALICE can correct for multiple spurious inductances and capacitances in the input divider circuit. Exponential compensation works best for overshoots and undershoots smaller than about 10% of the step height. In this case, a sum of exponential terms is an accurate generic model for such defects. | ||
+ | </ | ||
In figure In2 we show the new controls for the input compensation. To turn on and off the compensation for Channels A and B check boxes are added under the Curves drop down menu. Turning on compensation applies to both the Scope and Spectrum tools (time and frequency measurements). The filter time constant and gain settings can be set using new entry slots in the Settings Controls screen. The DC gain and offset adjust controls are unchanged. | In figure In2 we show the new controls for the input compensation. To turn on and off the compensation for Channels A and B check boxes are added under the Curves drop down menu. Turning on compensation applies to both the Scope and Spectrum tools (time and frequency measurements). The filter time constant and gain settings can be set using new entry slots in the Settings Controls screen. The DC gain and offset adjust controls are unchanged. | ||
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As we can see for this example the DC gain setting is slightly more than 2 which is to be expected based on the internal 1 MΩ resistor and external 1 MΩ R< | As we can see for this example the DC gain setting is slightly more than 2 which is to be expected based on the internal 1 MΩ resistor and external 1 MΩ R< | ||
- | The input gain factor of 2 (2.17 to be exact) increases the allowable measurement range from 0 to +5 V to about 0 to +10 V. Enough to work with circuits powered from a 9 V battery. If you have a 9 V battery try measuring it by connecting the - battery terminal to GND and the + battery terminal to the end of the 1 Meg resistor. You should read about +9 V for the DC average. | + | The input gain factor of 2 (2.17 to be exact) increases the allowable measurement range from 0 to +5 V to about 0 to +10 V. Enough to work with circuits powered from a 9 V battery. If you have a 9 V battery try measuring it by connecting the - battery terminal to GND and the + battery terminal to the end of the 1 Meg resistor. You should read about +9 V for the DC average. |
===Adjusting the compensation filter=== | ===Adjusting the compensation filter=== | ||
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=====Applying Digital Filtering: | =====Applying Digital Filtering: | ||
- | With this interface, ALICE Desktop can apply digital filtering to the captured Channel A and B voltage waveform data before being displayed in the Time and/or Frequency domains. ALICE uses the numpy convolve function to perform the filtering function. It is possible to have the program generate a simple Box Car (moving average) filter by setting the length and then clicking on the Box Car check box. | + | With this interface, ALICE Desktop can apply digital filtering to the captured Channel A and B voltage waveform data before being displayed in the Time and/or Frequency domains. Digital filtering can also be applied to the contents of the generated AWG waveform buffers as well. ALICE uses the numpy convolve function to perform the filtering function. It is possible to have the program generate a simple Box Car (moving average) filter by setting the length and then clicking on the Box Car check box. |
The supplied list of coefficients is convolved with the captured data buffer. The list of filer coefficients for either Channel A or B is first loaded from a single column .csv file by using the “Load CH A Filter Coef” and “Load CH B Filter Coef” buttons. The length ( number of coefficients ) and file name will then be displayed. The digital filter(s) will be applied to the voltage waveform data buffers if the “Filter CH A” and/or “Filter CH B” checkboxes are checked. | The supplied list of coefficients is convolved with the captured data buffer. The list of filer coefficients for either Channel A or B is first loaded from a single column .csv file by using the “Load CH A Filter Coef” and “Load CH B Filter Coef” buttons. The length ( number of coefficients ) and file name will then be displayed. The digital filter(s) will be applied to the voltage waveform data buffers if the “Filter CH A” and/or “Filter CH B” checkboxes are checked. | ||
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Alternatively, | Alternatively, | ||
- | The DFiltACoef and DFiltBCoef array variable are used to store the filter coefficients. The Filter formula coefficient scaling feature can be used to scale a set of filter values read from a file. First read in the values from the file and then simply pass the array through the formula function by entering DFiltACoef or DFiltBCoef for the formula. | + | The DFiltACoef and DFiltBCoef |
There are many filter design tools that can be found by searching the web. Here is one that works well but we are not necessarily endorsing it over any others that might be out there: | There are many filter design tools that can be found by searching the web. Here is one that works well but we are not necessarily endorsing it over any others that might be out there: | ||
- | http:// | + | [[http:// |
The array of coefficients ( filter taps ) that it generates as part of the C source code can be copy and pasted into a .csv file for use in ALICE. | The array of coefficients ( filter taps ) that it generates as part of the C source code can be copy and pasted into a .csv file for use in ALICE. |