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Laboratory Start-Up Procedure
Turn-on the Computer
Start the PC by turning on the power. When the startup display appears enter the username and password: Username: students, Password: power.
Turn-on the Lab-Volt Digital Acquisition Module (DAC)
The DAC is installed on the Lab-Volt test bench as shown in Fig. 1. It is powered by a 24 Vac supply that is part of the main power supply. The DAC is connected to the 24 Vac power supply
Figure 1. Lab-Volt DAC and Power Supply. DAC Module
Main Power Supply
24 Vac Power Cable Power-on LED
24 Vac Power Supply and Switch
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by a cable. When the 24 Vac supply is switched-on (red lever toggle switch), the DAC will turn on and the green LED will be lit. It is important that the green LED on the DAC remain lit at all times. If the power cable is disconnected, the acquisition software may stop recording test-data or turn off completely.
Activate Data Acquisition Software on the PC
In order to start the Lab-Volt data acquisition software (LVDAC-EMS) click on the icon on the desktop or use the sequence:
Start, Programs, Lab-Volt and LVDAC-EMS
After the program starts, the Module Selector panel will appear as shown in Fig. 2. The software is configured for 60 Hz and the DAC is in the connected mode. Do not check the box marked stand-alone mode. Click the box titled OK to continue.
Do Not check this box.
The DAC must be in Connected Mode.
Choose 60 Hz reference frequency
3 LVDAC-EMS Start Screen
When the DAC screen appears make sure the caption Connected-Mode appears in the lower right-hand side as shown in Fig. 3. Set the ranges if the voltage isolators (E1 etc.) and the current isolators (I1 etc.) by right-clicking on the far-right column in the section titled Range. Change the voltage isolators from Auto to High (800 V max). Change the current isolators from
the High range to the Low range (4 A max).
Change Voltage Ranges from Auto to High
Change Current Ranges from High to Low
The DAC must always be in Connected Mode Metering Icon
4 Start the Metering Function on the DAC
Click the Metering icon in the upper left-hand corner of the DAC display. The set of meters will appear on the screen. Since the test circuit is not yet turned-on, leave PC in this mode and continue to the next step – turning on the oscilloscope.
Turn-on the Oscilloscope
To power-on the LeCroy oscilloscope, press the start button at the lower left-hand corner of the
front panel as shown in Fig. 4.. Wait until the display prompts for username and password. Enter the Username: students and Password: power. Wait for the initial display as shown in Fig. 5 below.
Since the digital storage oscilloscope (DSO) is not yet connected to an active circuit, the trace may not represent any useful information. The vertical scale of the traces for channel 1 and channel 2 are adjusted in the subsequent steps. Note that at the bottom left-hand corner of Fig. 5
Figure 4. The LeCroy Oscilloscope Start Button
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there are two descriptor labels, one for each channel (C1, C2). Each label shows the vertical scale of that channel and the offset from the main horizontal axis (x-axis). In the upper right corner of each label there is an indicator of the type of coupling used by that channel. The labels in Fig.5 show DC1M which means that the channel is dc coupled with a 1 MΩ impedance. This is the preferred mode of coupling for this laboratory.
Adjusting the Vertical Scale of C1, Channel 1
Place the mouse cursor on the panel C1 in the lower left-hand corner of Fig. 5. Click to open the panel shown in Fig. 6. This panel is used to set the format of the oscilloscope display for C1, channel 1. Channel 1 has been set to correspond with the waveform that represents the phase voltage of a power circuit. Using this panel the adjustments are made for the vertical scale, offset, coupling, probe attenuation and labeling of the trace C1.
The scale of the y-axis is determined by first examining the ratio of the voltage-current isolator. In this case the Lab-Volt isolator yields 10 Vdc for a maximum input of 300 Vrms. The output
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of the isolator can be given by V1 where 𝑉1 = 208300 ∙ 10. Since the range of the measured voltage
is 0 - 208 Vrms, the isolator will output V1 = 6.9 Vrms . If the positive y-axis has 4 divisions
then at 2.0 V/div. (8.0 Vdc) the 6.9 V requirement can be accommodated. Thus the volts/div parameter is set for 2.0 V by using the arrows or by highlighting the numerical field or by entering the value using the keyboard. The Offset parameter is set to 0.00 volts so that
measurements are made with respect to zero on the vertical axis (y-axis, ordinate). The center of a sinusoidal waveform will be aligned with the major horizontal axis (x axis, abscissa) on the screen.
Adjusting the Trace Thickness
The quality of the trace, the thickness, can be adjusted by making three adjustments. 1) In the control panel of each channel, C1 and C2 there are controls to regulate a Noise Filter and the Bandwidth. Also, in the Timebase control panel, the maximum number of points can be varied. Click on a channel button, C1 or C2. In the lower right-hand corner of the panel that appears, there is a tab labeled Noise Filter (ERes). Click on the tab and in the drop-down menu choose the block +2.5 bits.
In the same channel control-panel there is a block labeled Bandwidth (upper center). Click on this button and in the drop-down menu choose the entry for 20 MHz.
In the Timebase control panel click on the tab labeled Max Sample Points. In the drop-down menu set the maximum number of points with either 500 kS or 10 kS for a very fine line..
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The coupling-mode is adjusted by activating the panel labeled Coupling. This should be set to DC and 1 MΩ input impedance (400 V max.). It is very important that this mode is used for all measurements in order to protect the oscilloscope from damage. The 50 Ω input impedance
C1, Channel 1, Phase Voltage
C1, Click here to open the panel.
Use Label to attach information to trace. Offset, Zero Offset
Vertical Scale, 2.0 Volts/div. Coupling is DC at 1 M Ohm
Probe Attenuation (multiplier) Label: Phase Voltage
Label: Phase Current
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can only tolerate 5 V rms maximum! The DC mode is used so that the screen will show both the AC and DC components in a signal. The probe attenuation is set to ÷1 or a unity
multiplication factor. use the 1.0 A rms range. The calculation of the scaling factor for the current should yield a setting of 1 V/div.
DC Coupling versus AC Coupling
Fig. 7 shows the difference between the DC coupling mode and the AC mode of the DSO. In Fig. 7(a) the output voltage of a rectifier is composed of a 253 V dc component combined with an ac ripple of 49 Vac peak-to-peak. The combination of the dc and ac components yields a
250 Vdc Offset
(a)
(b)
All values to be multiplied by 30
All values to be multiplied by 30
DC Coupling: DC + AC components
280 V
0 V
0 V
AC Coupling: AC component only
Figure 7. (a) DC coupling: dc voltage with ac ripple. (b) AC coupling.shows only ac waveform and hides dc component.
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waveform with a peak voltage of 302 Vpk and an RMS value of 280 Vrms. If the oscilloscope was
working in the ac coupling mode as shown in Fig. 7(b), the user could make the mistake of thinking that the only voltage present was 9 Vrms (49 Vp-p). This situation could be hazardous if
the source of this waveform were connected to a load that could not withstand a 300 V peak voltage or a dc voltage of 280 Vdc.
Adjusting the X-axis or Timebase
The scale of the x-axis can be adjusted by clicking on the Timebase panel shown in Fig. 8. The sampling mode should be set to RealTime. The Timebase Mode must be adjusted accommodate a 60 Hz signal. Since t = 1/f, each cycle will take 16.66 ms. There are two convenient time base
Timebase, y-axis control
Real-time mode 5 ms/div or 50 ms total time for x-axis Label: Phase Current Label: Phase Voltage
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values: 2 ms/div which shows a 20 ms time-span and yields 1 complete cycle and 5 ms/div which spans 50 ms and 3 complete cycles. Set the time base to 5 ms/div since 3 cycles will be required to compute some measurement functions.
In the Timebase control panel click on the tab labeled Max Sample Points. In the drop-down menu set the maximum number of points with either 500 kS or 10 kS for a very fine line.
Setting the Trigger Function
Trigger is set to the positive-going edge of trace C1. Phase Voltage is used as reference at t = 0 s with increasing positive value
Time t, sec Trigger at t = 0 s
Trigger source is C1, the phase voltage.
DC coupling shows DC and AC components of waveform.
t = 16.66 ms
Edge Trigger
Label: Phase Voltage Label: Phase Current
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The trigger control section is opened by clicking on the small trigger panel in the lower right hand corner of the screen as shown in Fig.9. For the experimental situations in the
undergraduate power lab the circuit analysis is referenced to the phase voltage and phase current at the load. The first variable of interest is the phase voltage. The trigger will be set so that the display of the oscilloscope will start at the instant that the phase voltage crosses the origin (t = 0.0 s, v = 0.0 V) in a positive direction. This point is at the center of the screen shown in Fig. 9. In order to capture this moment the trigger is set to the Edge-Trigger mode. The source of the trigger signal is set to channel 1, C1. The experiments in the undergraduate lab will use channel 1 of the oscilloscope, C1, to display the phase voltage. The capture of the reference signal is synchronized with the rising edge of the reference signal as it crosses the x-axis in a positive direction. Finally, The scope is set in the DC coupling mode. . If the source signal is very noisy, the HFREG mode of Fig. 9 may have to be used along with the Pre-Processing,
Averaging, and Sweep command of Fig. 6. The number of sweeps is raised until a cleaner signal is created. 4 or 5 sweeps may be required.
Measure Command Label: Phase Current Label: Phase Voltage
12 Waveform Measurements on the Oscilloscope
Start assigning the measurement functions by clicking on the Measurement command in the upper toolbar shown in Fig. 10. Then start the measurement set-up by clicking the panel shown in Fig. 11. The principal measurements are: the rms values of the waveforms and the phase angle between two waveforms (a phase voltage and a phase current).
Start Measure Function Label: Phase Current
Label: Phase Voltage
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The measurement selection display appears next as shown in Fig. 12. Each parameter to be displayed on the screen must be chosen by activating a channel and the measurement function that corresponds to that channel. By clicking on each panel associated with the block P1 a separate menu will appear and the selection can be made from the function choices. In this case, block P1, the channel is C1, channel 1. Clicking on the panel that indicates the word none will open the menu shown in Fig. 13.
Activate the rms measurement command by scrolling and clicking the panel marked RMS. As soon as the choice is made, the panel will close. The rms value of channel 2 is made by choosing the RMS function as before. The assignment of channel 2 is done by clicking the block currently connected to channel 1, C1, – a default condition – and changing the value to C2. The phase angle between the two waveforms is found by starting the Phase measurement command. In this case the channel assignments, C1 and C2 are done automatically since there are only 2 channels available on this oscilloscope. Also, 3 cycles (50 ms) must be displayed on the screen for the phase to begin operation. The final screen presentation will appear as shown in Fig. 14.
Click for RMS measurement assigned to P1 (C1) and P2 (C2)
Click for Phase measurement assigned to P3 (C1 and C2) Figure 12. The Measurement Selection Panel.
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Saving and Printing Test Results from the Oscilloscope
There are three ways to make a copy the screen of the LeCroy DSO for use in a lab report or other document:
Select Measure Function Select Channel(s)
Figure 13 RMS voltage and phase-angle measurement assignments.
Load Phase Angle
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1. Use the Print Screen command from the keyboard. This will place the image on the clipboard of the DSO. The oscilloscope screen can then be minimized and the Paint software opened from the accessories pull-down menu in Windows.
2. Print the screen directly to the printer.
3. Save the DSO display directly to a file on the host PC (not the oscilloscope).
Do not attempt to save any data to a memory device connected directly to the Lecroy oscilloscope. A USB memory stick will not function if connected to the oscilloscope and your data may be lost.
To use options 2 or 3, click on the File tab in the upper toolbar. Open the Print Setup tab from the pull-down menu as shown in Fig. 15. Use the Print Setup command to initiate the data save sequence. The Print command will transfer the data to a location or device pre-determined by the Print Setup options.
Choose Print Setup to print or save.
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Transfer the screen image and data from the oscilloscope to the PC or storage media (USB memory stick) using the functions shown in Fig. 16. The Print Setup has eight functions that configure the output:
1. The File option transfers the chosen screen area to a file on the host PC. 2. The printer option prints the chosen screen area to a printer.
3. The print color is black and white for best definition. 4. A format can be chosen for the output file.
5. A name must be given to the outputfile.
6. The default target PC (the host PC on the test bench) is identified. 7. The area of the DSO screen is determined.
8. Start the printer or a file transfer operation. File Option
Printer Option
Print in Black-White Target PC and Directory File Name
File Format Screen Area to Copy
Start Printer or File Transfer
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To begin, decide how the information on the DSO is to be transferred – to the printer or to a file. Activate the File icon to transfer the data from the LeCroy scope to the host PC on the test bench. Activate the Printer icon to print the results directly.
Set the Color option to black and white if desired. Use the File Format panel to select the type of data file –Bitmap (.bmp), JPEG (.jpg), Tagged Image File Format (.tif), Adobe Photoshop (.psd), or Portable Network Graphics (.png). Enter the name of the saved file in the File Name block. The Directory block shows the destination PC and directory. Do not change the
information in this field. Use the Hardcopy option to delimit the area of the screen to be saved. Grid Area Only is the minimum area available. Activate the printer icon in the lower left-hand-corner to start printing or transferring data
When the oscilloscope screen is copied to a file and printed, the image of the display is transferred to the host computer. The file will appear on the Windows desktop display in the directory My Documents. Figure 17 shows that the file transferred in Fig. 16,
Oscilloscope files in Directory: My Documents
Files that have been transferred in Bitmap format.
Figure 17. Files transferred from oscilloscope to directory My Documents on desktop of host PC.
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ManLabProc13a.bmp, is now displayed on the host PC, in this case, Conductance. The data file can now be saved to an external memory device such as a USB memory stick.
Printing or Saving Files from the LeCroy Oscilloscope to the PC
Printing
On the oscilloscope click on the File tab in the menu on the left-hand-side of the display.
To print a screen image choose Print Setup on the oscilloscope. Make the following settings on the oscilloscope display.
Choose Printer Colors: Black&White
Select Printer: \\localpcname\HP Laserjet 1200 Series PCL5
The local printer could be \\redistortion\HP Laserjet 1200 Series PCL5 Hardcopy Area: Grid Area Only
Click on the printer icon in lower right-side corner to start printing.
Saving to a File on the Local PC
On the oscilloscope click on the File tab in the menu on the left-hand-side of the display.
To print a screen image choose Print Setup on the oscilloscope. Make the following settings on the oscilloscope display.
Choose the File tab
File Format: Windows Bitmap 8bit (.bmp) Colors: Black&White
Filename. Type in: yourfilename.bmp Directory: \\localpcname\Student_Docs
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Click on the printer icon in lower right-side corner to start transferring your file to the local PC. The file will appear under
Computer →Libraries →Documents and yourfilename.bmp or Desktop →Students Folder →My Documents and yourfilename.bmp
20 Connecting a Circuit with the Lab-Volt Equipment
A basic circuit diagram consisting of a source, a load and voltage and current measurement devices is shown in Fig. 18. The labels and circuit element identifiers in this diagram correspond to the markings on the panels of the Lab-Volt equipment. Note that there are three types of measurement devices indicated by the component blocks:
1. Physical analog and digital meters are represented by circles and the letters V, A, or DMM.
2. Transducers sense a voltage or current and send an isolated signal to the oscilloscope. 3. Transducers sense a voltage or current and send an isolated signal to the host PC. The first type of meter consists of analog ac or dc voltmeters and ammeters. The digital multimeter (DMM) is included in this group. The isolators designed to be used with the oscilloscope are labeled with a lowercase letter and possibly a numeral placed inside a box. Examples are i for a current isolator and e to indicate a voltage isolator.
The third type of transducer is located on the Lab-Volt digital acquisition and control module, LVDAC, that is shown in Fig. 1. This unit isolates signals from the active circuit and transfers them to the Lab-Volt software on the host PC. These circuit elements are represented as squares with capitalized labels that are identical to the markings on the DAC. The letter-number
combination E1, for example, represents a voltage sensor.
Observe the standard polarity scheme when connecting the Lab-Volt meters and isolators. The high or positive side of a meter is the red terminal (connection jack) or a jack with a value – 250 V, 0.5 A - associated with it. The low side of a meter or isolator is identified by the black
connector or a ± label. Thus a current enters an ammeter at the terminal colored red or marked with a value (such as 0.5 A) and leaves at the terminal colored black or marked with the character ±.
When wiring a circuit, connect the current path first and then add the voltage measurement devices in parallel to a common set of high and low terminals. The current path should follow a continuous series of connections from the source through the ammeters to the load. There should not be any branches or splitting of the circuit. Do not jump or share terminals or connections at
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the meters or isolators. For example, the low-side connection of an ammeter or current isolator DMM
A
3 Phase VariacV
0- 208V 0- 208V 250Vac 4 5 6 I2 To DAQ To DAQ E2 I1 T o DAQ To DAQ E1 + + + + i e To Osc. To Osc. DMMA
3 Phase VariacV
0- 208V 0- 208V 250Vac 4 5 6 I2 To DAQ To DAQ E2 I1 To DAQ To DAQ E1 + + + + i e To Osc. To Osc. Current Path Current Path Current Path (a) (b) DMMA
3 Phase VariacV
0- 208V 0- 208V 250Vac 4 5 6 I2 To DAQ To DAQ E2 I1 T o DAQ To DAQ E1 + + + + i e To Osc. To Osc. (c)Figure 18. The basic circuit diagram: (a) the schematic, (b) the current paths, (c) current and voltage meter connections.
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should not be shared with the high side of a voltmeter. The terminals of the voltmeter should be connected directly to the corresponding terminals of the device or source that is being measured. This strategy will use more wires but it will result in fewer errors and the circuit will be easier to troubleshoot.
Using the Lab-Volt Metering Function
Before starting the Lab-Volt metering, open the Windows Excel spreadsheet software. The data collected in the Lab-Volt data table will be transferred to Excel for calculation and plotting. The Lab-Volt start screen was opened at the start of this exercise. Click on the Metering icon at the top of the display. The meters will appear as shown in Fig. 19. Note the default settings of the
Metering Icon opens the metering display Start the data table
Continuous Refresh button
Meter, M1, is voltmeter E1 on the DAC
E1 is measuring Volts E1 is measuring ac rms values
Ammeters set to low range Voltmeters set to high range
The software and PC are always in Connected Mode
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meters. Meter M1, is set to correspond to the DAC connections for E1. This meter is set to record ac, rms voltages. To start the meters click on one of the refresh buttons. The continuous refresh button will update the values of the meters every second. Note that the voltmeters have been set to the high range (800 V) and the ammeters set to the low range (4 A).
Using the Lab-Volt Data Table The Data Table and the set-up menu (Record Settings) are shown in Fig. 20. Open the data table with the icon in the toolbar at the top of the window. Activate the columns (A, B, C etc.) by checking the appropriate meters in the Record Setting window.
x
x x
Click on the Record Settings icon to open the setup window Click on the Data Table with Pencil icon to record measurements
Click on M1-E1 assign column A to meter M1
Click on M13 to assign column C to measure power for E1-I1
Click on M7-I1 to assign column B to meter M7 Plot command for data table
START the data table with this icon
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Measurements can be recorded by clicking the icon that features a pencil. This action will transfer the values shown in the metering panel to the Data Table. Note that the metering panel also has a button that allows the data to be transferred without maximizing the Data Table. Figure 21 shows an example of the Data Table with meters assigned to the columns. One set of data has been recorded. Note that after the data is recorded, the rows in the data table can be highlighted and copied (to the clipboard). Once copied, the information can be pasted in to an EXCEL spreadsheet.
Transferring Data to Excel
Figure 22 shows a row of data that has been pasted into the Excel spreadsheet. The first row has been left blank so that the column headings can be copied from the Data Table. The data should
Click here to Record Data from Metering Plot Data function
Recorded value of meter M3 which is assigned to voltage isolator E3
(Vac,rms)
Column D assigned to meter M7
Figure 21. The Data Table with columns assigned to meters. A set of measurements is recorded in the first row.
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be transferred from the Data Table regularly and the Excel sheet should be saved so that no information is lost if the Lab-Volt metering or the DAC are interrupted. Safeguard the experimental data by updating and saving the spreadsheet regularly. The Excel platform can be used to perform calculations related to the experimental results. Also, the Excel software can be used to plot the experimental performance curves.
Plotting Data with Excel
Experimental data that has been copied from the Lab-Volt data table can be plotted after it has been transferred to the Excel spreadsheet. Figure 23 shows a data set on an Excel spread sheet. In order to plot a single set of data – an x-axis and a single y axis – two columns, A and B, have been highlighted (step 1). The first values contained in column, A, will become the x-axis and column B will be the y-axis. Next, the Insert tab is clicked on the upper toolbar (step 2). The Scatter plot with a smooth curve is chosen (steps 3 and 4). The result is shown in Fig. 24. Note
Data copied and pasted from Lab-Volt Display
Column Headings must be typed in same order as Lab-Volt table E1, Vac I1, Aac
Notes typed in Excel sheet
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that the plot does not have a label for the data, the axes, or the plot itself. The next step is to identify the curve and the source of the data from the spreadsheet.
The labels can be added to the plot or edited by using the Chart Tools function. First click on the plot area to activate the chart panel (step 1). Then choose the Layout tab in the upper toolbar (step 2). By activating the icons named Axis Titles and Chart Title, the axes can be labeled (step 3). The new title for the x-axis is shown in step 4. To change the text of the Series Title the following sequence is followed: click the series title text. A box containing the text will appear. Right click on the box. Choose Select Data from the menu that appears. Next a panel titled Select Data Source will appear. In the Select Data Panel highlight the text: Series 1. Now choose the edit tab. Change the series name and click OK to close the window. This procedure, changing the text of the Series Title (step 5), is shown in Figs. 27 and 28.
1. Highlight 2 columns. Column A is the x-axis.
2. Click on INSERT 3. Click on Scatter Plot.
4. Choose smooth curve.
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Creating plots that use 2 axes is sometimes necessary to compare curves or make calculations directly from the plot. The procedure is shown in Figs. 25 and 26. Three columns of data are highlighted in the Excel sheet. The Insert and Scatter Plot functions are used as shown
previously. As shown in Fig. 25, one curve (column B, Iph) is unreadable because the scale of the y-axis, taken from column C, is too large. To correct this situation, a second y-axis must be added.
To create a second axis first click on the curve that requires the new axis (step 3). Right click on this curve and a menu appears. Choose Format Data Series from this menu. A Format Data Series panel will appear (step 6). Choose the button: Secondary Axis to create the new y-axis.
1. Click on the plot figure.
2. Choose Layout on Toolbar.
3. Choose Axis Titles.
4. New axis title .
5. Series title .
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The result is shown in Fig. 26. The values of the new secondary axis appear on the right side of
the plot. Note that the phase-current trace, Iph, is marked by a series of linked symbols. Figure 26 shows the plot with a second y-axis added on the right side of the figure.
Using the Lab-Volt Phasor Analyzer
The Lab-Volt software includes several useful utilities that correspond to standard methods of representing and analyzing electrical power circuits. The phasor analyzer display is shown in Fig. 27. The utility is activated by clicking on the icon located on the upper toolbar. After the screen appears the circuit parameters are chosen from the menu on the right. In this case the angle between a phase voltage, E1, and a phase current, I1, is shown. Note that the phase
1. Three columns to be plotted. Highlight the columns. Use INSERT and SCATTER to plot. 2. Columns B, C are on same y-axis. Column B,
Data Series 1, can’t be seen.
3. Click on curve B, Data Series 1. 4. Format Selection, Series 1, appears.
5. Format Data Series command.
6. Data Series 1 is initially assigned to Primary Axis.
Click on Secondary Axis to
create new axis.
* Column A is the x axis.
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voltage E1 is chosen as the reference phasor. The load angle is shown at the bottom of the display. The angle is associated with the current and appears under the column labeled Phase.
Using the Lab-Volt Harmonic Analyzer
The Harmonic analyzer display is shown in Fig. 28. The utility is activated by clicking on the icon located on the upper toolbar. After the screen appears the circuit parameters are chosen from the menu on the right. In this case the frequency of the fundamental is chosen from the default system value of 60 HZ. The parameter to be analyzed is the phase current and the harmonic components are given as amperes. The components could also be evaluated as
percent’s of the fundamental. The number of harmonics to be evaluated is 10 with the possibility of measuring a total of 40 components.
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Fig. 28. The Harmonic Analyzer. 1 Fig. 27. The Phasor Analyzer.
31 Using the Lab-Volt Oscilloscope
The Lab-Volt software includes an oscilloscope that is activated by an icon in the upper toolbar. This utility functions in the same manner as an actual instrument.
