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UT ASE 369K - LAB 3- Virtual Instruments- Behavior of Second-Order Systems

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1LAB #3: Virtual Instruments; Behavior of Second-Order SystemsEquipment: Dell Optiplex Gs+ Pentium computerNational Instruments BNC-2140 signal connector box, PCI-4451 dynamic signal acquisition board, and VirtualBench virtual instrument libraryMultimeter (FLUKE 8050A)Function Generator (Tektronix CFG250)RLC CircuitOscilloscope (Tektronix 2211) (Optional)Objectives:In this experiment, you will study the behavior of a second-order system represented by anRLC circuit. You will use a personal computer as an oscilloscope to acquire data. Fromthis experiment, you should achieve a grasp of the concepts of natural frequency, damping,and frequency response.A secondary purpose of this experiment is to introduce you to virtual instruments. Youshould already be familiar with the basic operating principles of an oscilloscope and a PC.The virtual oscilloscope has some features that are not normally found on traditionaloscilloscopes; these are described below.1 VIRTUAL OSCILLOSCOPEThe virtual oscilloscope (VI) used in this experiment is designed to emulate the functions ofan actual four-channel oscilloscope and allow the user to exploit the versatility of a personalcomputer in manipulating acquired data. Essentially, a virtual instrument is software thatenables a personal computer to act as a piece of hardware; in this case, it acts as anoscilloscope. The virtual oscilloscope was created by National Instruments as part of aVirtual Instrument Library called VirtualBench. Signals are brought into the computerthrough a National Instruments PCI-4451 dynamic signal acquisition and generation board.This board converts analog signals into digital signals, which can be manipulated by thecomputer.1.1 OperationsFirst, turn on the computer, if it is not already on, and log onto the system as a Guest.This is done by pushing the power button on the front of the machine and the power buttonon the monitor and following instructions. Double click on the Scope icon on the desktop.The “front panel” of the scope will be shown on the screen. This panel simulates the frontpanel of a traditional oscilloscope and contains a display area plus a variety of knobs andbuttons. These are controls that can be manipulated with the mouse. There are also pull-down menus, where some of the settings are located, as well as file management controlsand online help. To understand the operation of the VirtualBench Oscilloscope, let usbegin with a discussion of the items on the front panel.1.1.1 The display on the front panel looks very similar the display on a traditionaltwo-channel oscilloscope, except that it also displays vertical divisions, the verticalposition, and the timebase in the upper left hand corner of the display. Also, if any2measurements are requested, they are displayed below the trace(s) at the bottom of thedisplay. Up to eight measurements can be displayed simultaneously.1.1.2 Below the display are four “push” buttons and a slider bar, which is hiddenif one of the buttons is depressed. If the Run button is depressed, the scope will acquiredata continuously until the button is pressed again. If you press the Single button, thescope will acquire one frame of data and display it on the screen. If the Autosetup buttonis depressed, the software will determine the “best” setup for you. It is preferable if thisfeature is not used, and you determine the best setup yourself. The Mode button has twosettings, Y-T and X-Y. If the Y-T mode is selected, the display will have voltage on the Y-axis, and time on the X-axis. If X-Y is selected, the X-axis will show the voltage of CH1and the Y-axis will show the voltage of CH2. The slider bar, which is marked X<>,adjusts the point where triggering will occur. Normally, the slider bar, which moves thetrace horizontally, is left in the left-most position.1.1.3 To the right of the display are several areas that contain buttons and knobs.The Channels section contains buttons for switching on and off the different traces. Forexample, if the button for Ch 1 is green in the center, the trace for the signal should be seenon the display. If the button is not green in the center, the trace will not be be shown on thedisplay. Each trace can be displayed in a different color. To the right of the Channelssection are two knobs and a channel-selector switch. The switch is used to select an activechannel that you want to adjust using the two knobs. The first knob is for adjusting thescale of the trace by changing the volts/division of the display for that trace. This setting isdisplayed at the top-left corner of the display area. The second knob is for adjusting thevertical position of the trace on the display. Note that a colored triangle at the right edge ofthe graph area indicates the vertical position of the zero-voltage level for each active trace.The Timebase knob adjusts the (horizontal) time scale of the display by changing thenumber of seconds per division. This setting is listed just above the graph area. TheMeasure indicator box is used to determine which channel’s data is to be used incomputing the requested measurements to be listed at the bottom of the display. Some ofthe selected measurements are not displayed if the cursors are active. The Cursors sectionis used to provide cursors on the display for making measurements. If the cursors buttonis not depressed, the cursors will not be seen on the display. When the cursors are active,two cursors will be attached to the selected trace, and the coordinates, as well as thespacing between them will be displayed with the measurements at the bottom of thedisplay. Large adjustments to the cursor location can be made by simply using the mouseto move the line attached to the cursor. The four cursor arrow buttons can be used formaking fine adjustments. The bottom selector in the Cursors section allows the user to setthe location of the trigger cursor. The mouse may also be used to move the trigger cursor.The last section on the front panel is the Trigger controls section. Depending on whichtrigger mode is selected, other boxes will appear in the trigger control section. You shouldonly need to use the NORMAL mode, or no trigger at all (NONE). For all types of triggermodes, except NONE, the slope box will be available, and the trigger crosshair cursor willbe available for setting the trigger level and trigger delay. For the NORMAL mode you willalso need to select the trigger


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