Electrical Engineering Laboratory Equipment Instructional Videos

Transcription

1 Summary In this project, instructional videos demonstrating the use of common laboratory equipment were created. The videos include the safe and proper use of DC power supplies, function generators, and oscilloscopes. These videos will help to maintain continuity of instruction for local and collaborative engineering students throughout the state. Completed Work Five instructional videos were created and posted on YouTube. These videos cover the use of a DC power supply, breadboard, function generator, and oscilloscope, including how to properly connect circuits to the equipment and how to interact with the equipment using a computer, when possible. All videos have are captioned (transcripts are attached). Actual recording using the laboratory equipment was completed prior to the June 16 tornado; however, because of the lack of access to the facilities, considerable post recording adjustments had to be made, both in the original plan and the technology used for the video production. This required some extra training and instruction from Tyler Tollefson from Media Technology Services on the use of video editing software, increasing the time involved in producing the videos. Videos designated as time- permitting in the proposal were not completed at this time. Knowledge and skills gained in the creation of these videos will facilitate the creation of future videos covering other instructional videos covering both laboratory equipment (when facilities are available) and course material. Sharing the Results Videos are available on YouTube and are available to instructors on the local campus, as well as instructors at the thirteen collaborative engineering program sites. DC Power Supply Function Generator Oscilloscope Overview Oscilloscope Measurement Oscilloscope Wintek32 Interface Information on the availability of these videos will be disseminated through the Collaborative Engineering Laboratory Managers, in addition to being posted on the Electrical Engineering Department website. 1 of 15

2 DC Power Supply Transcript While there is a large variety of electrical test equipment, some of which are far more interesting, we generally begin with the DC power supply. I can think of two very good reasons for this: 1) DC voltages are simple. 2) Without DC the more interesting circuits tend not to do anything. DC, or direct current, simply refers to electrical phenomena that are constant in time. The term DC is used interchangeably to refer to voltage (the pushing power for electricity) or current (the flow of electrical charge). Because of this, you may hear people use the seemingly redundant term DC current, but this is necessary to differentiate it from DC voltage. As I was saying, DC refers to electrical phenomena that are constant in time. Another way of stating this would be to say that DC phenomena have a fixed polarity. Polarity is the difference between the positive and negative terminals of a battery, comes from the fact that there are both positive and negative charges, and means that direction is important with electricity (any of us that have made a mistake with positive and negative in an electric circuit know this all too well). We use DC to provide power to circuits. Things like phones, music players, automotive systems, and low- voltage lighting systems use DC power. The most familiar DC power source may be the battery, though an argument can be made for the wall chargers we use for all our portable devices. DC is necessary for many circuits to operate. In the laboratory we want to have a safe, reliable source of DC power that we can configure to supply a variety of voltage and current levels. An example of such a source is the Agilent E3630A triple output voltage supply. If we look at the front of the supply we can see that there are five terminal outputs. (Hold it! you just said it was a triple output supply, not a quintuple output supply). Voltage is a difference in electrical potential between two electrical points (called nodes). For a three voltage outputs, each of the voltages must be relative to some common point they share, hence the fourth terminal called common. The fifth terminal is connected to earth ground. We use earth ground as an absolute reference for voltages on earth. The fifth terminal is not directly connected to the other four terminals, and for most circuits used in introductory classes, can be ignored. Let s briefly go over the rest of the front display. Here we have the power supply s display. This will display the electric potential in volts and the current in amps of whichever channel is selected by the meter buttons. The meter buttons do not affect the output of the supply; they only change what is displayed on the indicator. Other important indicators we have on the front panel are the overload indicators. If any of these are lit up it generally means that we have a short circuit between power and ground. If any of these are lit up we should turn off the power supply immediately so that we do not damage our circuit. 2 of 15

3 The plus six volt knob controls the potential between the six volt output and the common terminal. The plus or minus 20 volt knob controls the voltage difference between the common and the 20 volt outputs. The tracking ratio knob determines if the negative 20 volt output has the same absolute value as the positive 20 volt output. When it is set to fixed, both of the 20 volt outputs will have the same absolute magnitude, but one will be positive and one will be negative. The last thing I will point out on the front panel is the power button. This turns the power supply on and off. Now that we have a general orientation to the DC Power supply s front panel, let s take a look at it in operation. Here we are set up so that we can see the output of each of the voltage terminals relative to the common displayed on digital multimeters. I ve used banana plug connectors to connect the power supply to each of the multimeters. Notice that all of the common terminals are connected together. The left hand meter will display the output of the six volt terminal. The center meter will display the output of the positive 20 volt terminal. And the right- hand meter will display the output of the negative 20 volt output. I ll start by turning the voltage knobs fully counterclockwise. Then I will turn the power supply on. The display of the power supply and the displays of the multimeters show zero volts right now because nothing is on. If I press the button for the 6 volt meter and turn the voltage knob on the 6 volt supply we see that the voltage is displayed on both the power supply s display and on the multimeter s display. Sometimes there is a slight difference between these two measurements. That is why it is important to use only one device to measure all of the voltages during a project. In most cases where we are dealing with DC voltages, that will be a single digital multimeter. This will increase the consistency of our data. While this does not increase the accuracy of our results, it does increase the precision, or repeatability, of our measurements. If I then turn the plus or minus twenty volt knob clockwise, we see that the multimeters connected to those outputs now register an increase in voltage and those voltages have the same magnitude with one positive and one negative. Note that the display on the power supply did not change because I did not move the 6V knob. The display and the meter buttons have no effect on the actual output of the power supply. They are just there so that we have a quick way to see the approximate output voltage of the selected channel. If I select the different meter outputs, the values on the digital multimeters do not change. Let s see what the tracking ratio knob does. Watch the multimeter on the right. As I turn the knob counter- clockwise the output of the minus 20 volt output decreases while the output of the plus twenty volt output remains the same. This gives us some extra flexibility in the output voltages that we can obtain. An exercise I have often given to help students understand the dc power supply is to set up the power supply so that several voltages can be obtained at the same time without making further adjustments. If you understand voltage and how the power supply works it should 3 of 15

4 be fairly easy for you to set up the power supply so you can measure positive 4 volts, positive 16 volts, negative 10 volts, and negative 14 volts without adjusting the power supply. If you think you understand how this might work, and you are near a power supply, I encourage you to pause the video and give it a try before continuing. Now I will demonstrate. Since 4 volts is the smallest potential and is less that 6V, I will use the 6V output to obtain it. And I m going to call that close enough. To get positive 16 volts I will need to use the positive 20 volt output. The negative 10 volts can be obtained by adjusting the tracking ratio so that the negative 20 volt output gives us that one. Now we need a little creativity. We ve used up all of the power supply s outputs, and I still asked you to get a negative 14 volts. Remember that an electric potential is just a difference between two points. All we need in order to measure negative 14 volts is to find two points that are 14 volts apart and then choose the correct polarity. The negative 14 volts is between the minus 20 volt output and the plus 6 volt output. Since we are here we might as well take a quick look at how to connect the power supply to what we build our circuits on for temporary laboratory projects the breadboard. A brief overview of breadboards Breadboards look like an array of holes. Behind each of these holes is a metal clip. When a wire or component lead is inserted into the breadboard, the clip firmly contacts the lead and an electrical connection is made. There are two types of arrangements of clips within the board. The center of the breadboard (or section of breadboard if we have a larger breadboard) is used to build our circuits. In the center of the breadboard there are groups of holes labeled with numbers and letters for reference. The clips behind those holes are arranged to that holes A- E in each of the numbered rows are connected, as are holes F- I. When we are building a circuit we use each of these groups of five as a node. The outside of each section of breadboard has long clips. We generally use these to distribute power to our circuit. Very often power and ground will be used at several points in a circuit, so it is neater and more convenient to have power and ground available in a larger area. All the points adjacent to each of the solid lines are connected. If there is a break in the line that means the clip is not continuous for the whole length of the board. Whether the clips are continuous or not varies from breadboard to breadboard, so be sure to pay attention to the lines. To bring power from the power supply to the breadboard, a banana plug connector is used to connect the power supply to the binding post of the breadboard. The binding post of the breadboard can unscrew, revealing the post has a hole in it. If we insert a jumper wire into that hole and then tighten the binding post, we can insert the other end of the jumper wire into the power strip on the breadboard. This will make whatever we connect to the binding post available along the entire length of the solid line. If we want to bring power into a particular point in the circuit area of the breadboard, all we have to do is use a jumper wire 4 of 15

5 from the power strip to any node we want. Once we have connected the banana connector to the power supply, everything connected to the red wires is connected to the power supply. This concludes the introduction to the DC power supply. Hopefully that will give you a head start when you get into the laboratory. Oh yeah go out and make it a great one! Function Generator Transcript Today we're going to look at the Agilent 33210A function generator. The purpose of a function generator is to create different shaped time varying signals. Let's begin by looking at the front panel of the function generator. The primary purpose of the function generator is to generate a variety of electrical signals. There are six different types of waves that this function generator can supply. In addition, each of these waves can be configured in a variety of ways. When it comes to generating the waves I'll focus on the first three types we can produce: the sine wave, the square wave and the ramp wave. The characteristics of the waveform are shown on the display above the buttons. I prefer to use the numeric display for adjusting the parameters, but if you prefer a pictorial representation, the graph button can be used to toggle between the graphical and numeric display. For a sine wave the primary attributes that we can adjust are the frequency, which can be selected by pushing the button below the frequency on the display; the amplitude can be adjusted by pushing the button below that display, and, if we desire, we can add a DC offset which can be adjusted by pushing the button below that display. The DC offset will simply shift the sine wave up or down on the vertical axis. The values for each of these parameters can be adjusted in a couple of ways. One is to use the numeric keypad. From here we can directly enter the value that we want. We can also just the values using the knob. The knob will adjust whichever character is highlighted on the display. The buttons below the knob allow us to adjust which character is highlighted so that we can choose which value we are modifying. These buttons allow for advanced more advanced waveforms such as a modulated waveform, a frequency sweep, or a burst of a single waveform. The trigger button allows for manual triggering of the sweeper burst functions. We will not deal with those in depth in this video. The store/recall buttons in the utility buttons have to do with the setup of the function generator and are not required for basic operation. The help button is pretty self- explanatory. There are two BNC outputs on the function generator one is labeled sync and one is labeled output. The sync outputs a square wave at the same frequency of whatever waveform is chosen. This allows us to synchronize another instrument with the function generator. The output is where the actual waveform is present. Note that in between these two outputs 5 of 15

6 there's a label that says 50 Ohms. This is the equivalent resistance of the output. That can be important if we want to figure out what the actual output is going to be for varying loads. Finally we have the power button which turns the device on and off. For purposes of this demonstration I ve connected the output of the function generator to channel one of the oscilloscope and the sync output of the function generator to channel two of the oscilloscope. This will allow us to have a picture of the waveforms as I make changes to the function generator. If you want to understand the operation of the oscilloscope, there are other videos covering its operation. When we initially power the function generator on it initially is set to output a sine wave of a frequency of 1 khz and an amplitude of 100 millivolts peak- to- peak with a zero volt DC offset. To get the wave to actually display on the oscilloscope I simply push the output button on the function generator. To see the difference in displays on the function generator we can switch from the numerical to the graphical display by pressing the graph button, at which point we see there is a 1 khz, 100 millivolt peak- to- peak signal being generated. You may notice that the wave form shown on the oscilloscope has twice the amplitude of the waveform on the function generator. That is because of the 50 ohm equivalent resistance of the output of the function generator. To understand this you may need to watch the video on equivalent circuits. I ll go back to the numeric display so we can see some of the things that can be adjusted. We ll stay on the sine wave for now. If I use the knob, it adjusts the frequency at the digit that is highlighted. If I increase the frequency the waves happened more quickly and as I decrease the frequency the waves spread out. I can adjust how quickly I change the frequency with the adjustment knob by changing which digit is highlighted. I can use the arrow buttons below the knob to select the digit I want to adjust and now I m adjusting, instead of by steps of 100 Hz, by steps of kilohertz and we see the waves change much more quickly. I can also enter in a frequency directly on the keypad. For example, I could and enter 100 and then press the kilohertz button. I ll have to adjust the oscilloscope so we can see the waves. We see on the oscilloscope that we have a 100 khz sine wave. If I want to increase the amplitude of the output I press the button below amplitude. Now I can enter in a value of, for example, one volt peak- to- peak. Then after adjusting channel one of the oscilloscope, we see the waveform looks the same but, if we look carefully, the numbers on the oscilloscope show that the amplitude of the output has increased. Other options I had for the amplitude were to enter in millivolts peak- to- peak millivolts RMS or volts RMS. Just for fun I m going to enter in one volt RMS and we ll see that this actually produces a sine wave with a much higher amplitude the we might have thought it would have. That is because, for a sine wave, the RMS value is the peak voltage divided by the square root of two. So when I enter 1 volt rms on the function generator, I get a peak voltage of about 1.4 volts, which is 2.8 volts peak- to- peak. But because the output resistance of the function 6 of 15

7 generator is low, and there is no load resistor, the oscilloscope is displaying a peak- to- peak voltage of just over 5.6 volts. To see the effect of the offset voltage I ll adjust the offset to - 1 volt and we can see that the sine wave remains the same but it is shifted down. You may have noticed that the sync, or synchronization wave, has stayed basically the same regardless of the changes I am making, with the exception of the frequency. That is because the purpose of the sync wave is to provide a frequency reference for other devices, so only the frequency changes affect the output of the sync wave. Now let s change the output of the function generator to square wave. Since we have a square wave at the output, I m going to turn the display of the synchronization wave down so we can clearly differentiate between the output of the function generator and the synchronization wave. With the square wave we have the same options for adjusting the frequency and the amplitude that we had with the sine wave, and we can also adjust the DC offset up or down if we desire. An additional adjustment we have something called a duty cycle. A square wave has two levels, a high voltage level and a low voltage level. The duty cycle of the square waves is the percentage of time that the wave is at the high voltage. So if I were to enter and a duty cycle of 20% that means the wave would be at the high voltage 20% of the time and at its low value 80% of the time. We see that adjustment on the oscilloscope. I can adjust the duty cycle between 20% and 80%. A reason we might want to adjust the duty cycle of the square wave would be to adjust the effective output power of the waveform for applications such as pulse width modulation. Let s move on to the ramp wave. Here we see an output voltage that increases linearly up to a point and then starts over. Many of the same adjustments are here. We can adjust the frequency of the wave, the amplitude of the wave, or the DC offset of the wave. Another option we have is the symmetry of the wave. On this function generator 100% symmetry is a ramp wave. As I turned the symmetry down to 50% we get a triangle wave. And if I turn the symmetry down to 0% we get a backward ramp wave. To return to original the ramp wave I can simply enter in 100 and hit the button below percent of the display. That covers the basic functionality of the function generator. To review the basic outputs we have a sine wave where we can adjust the frequency, the amplitude, or the DC offset. We can do the same of the square waves with the addition of having the adjustable duty cycle. For the ramp wave we have the added capability of adjusting the symmetry to obtain a triangle wave. Hopefully that s enough to get you started with using the function generator. To reiterate, the purpose of a function generator is to create different waveforms so that we can see how our circuits respond to them. 7 of 15

8 That s all for today, go out and make it a great one! 8 of 15

9 Oscilloscope Overview Transcript In this video I am going to demonstrate how to use a Tektronix TDS 210 two channel digital real time oscilloscope. The purpose of an oscilloscope is to give as a visual representation of electronic signals that exist within our circuits. This will help us in understanding how electrical signals behave and often allows us to diagnose problems within a circuit If you watched the video on the function generator you saw that the oscilloscope displays the output waveforms from the function generator. During that video, I did make some changes to the oscilloscope while making that video so that we could see the waves more clearly. So now I will go over how to make those changes as we go on the oscilloscope. To begin let s go over the front panel display of the oscilloscope. The most prominent feature of the front panel of the oscilloscope is the screen on which the waveforms are displayed. The vertical axis displays how the waveform changes in amplitude or voltage. The horizontal axis displays how the waveform changes in time. Looking closely at the screen we see it is divided up into a grid. Each of the subdivisions of the grid is called a division. What each of those divisions represents is shown on the bottom of the screen. We see that for channel one each division here represents 100 millivolts and for channel two each division represents one volt. So, for channel one from the top of the wave to the bottom of the wave is about two divisions. Since it is 100 millivolts per division that means this wave is 200 millivolts peak- to- peak. For channel two in each division represents one volt. From the top of the wave to the bottom of the wave there are about 3.4 divisions at one volt per division. This gives us a value of three point four volts peak- to- peak for the waveform. The horizontal axis is also divided by the subdivisions. In this case, the divisions for each of the channels remain the same and is 500 microseconds per division. If we look at the square waves, and we looked at the starting voltage of two successive waves, there are two divisions at 500 microseconds per division which results in a time of 1 millisecond. If we remember that the relationship between period and frequency is an inverse relationship, we notice this corresponds to a frequency of 1 khz which is one divided by 1 ms. Knowing the relationship between the period of the wave and its frequency is very important for being able to display waves of different frequencies on the oscilloscope as we will see later. Channel one is controlled by these three controls. Channel two is controlled by these controls. We can adjust the position of the wave on the screen which refers to the point indicated by the numbers one and two on the left- hand side of the screen. For each of these waves this is the point that is considered as zero volts. The volts represented by each division is controlled by these two knobs. The left- hand of knob controls channel one and the right- hand knob controls channel two. 9 of 15

10 The volts per division can be set independently for each channel. The third set of controls adjusts the horizontal axis or the time axis. We can adjust the time equals zero point and our the seconds per division to look at different frequency signals. The right- hand set of controls refers to the trigger. Since we are looking at time varying signals, we need to tell the oscilloscope at what voltage level it needs to start looking for a signal. If we do not set a trigger level, the waveforms will roll across the screen and we will not be able to see a stable waveform. The trigger level or the voltage level at which it starts to look for waveform is indicated on the right- hand side of the screen. On the far right of the screen we see there is a menu of options. The button just to the right of each of these is the input for that option. So, this button corresponds to this menu item, this button corresponds to this one, and so forth. Up at the top we have a group of buttons called menu buttons. These correspond to some functionality of the oscilloscope that I will show you later. Other buttons on the front panel include the hardcopy button. By default this button will send an image of whatever is displayed on the screen via RS 232 protocol. In our laboratory, this output is connected to the computer on the lab bench and there s a program on the computer called Wintek32 which will receive the image and allow you to save the image to the computer. The run/stop button controls whether the oscilloscope is actively grabbing signals or if it is just holding onto the signal that it had when the button was pressed. If the run/stop button is pressed so that the oscilloscope is in the stop mode the oscilloscope will display whatever was on the screen when the button was pressed. The last button on the front panel that I will talk about is the autoset button. This button is only necessary when we have no idea what to expect. Since we understand the relationship between period and frequency, and we have at least a basic idea of what our circuit is doing we should always know what settings to manually put onto the oscilloscopes that we should never use this bottom. This button is not for electrical engineering students. Lastly, the power button for the oscilloscope it on the top left hand side of the scope. Alright, a couple of things have occurred since I started making this video. First and most significantly, a tornado hit the campus, including the building in which I work. It wasn't destroyed, but because of the damage, it will be at least a couple months before I can get back into the building. This means I have to make some adjustments to my filming and editting techniques. Second, I realized that the original video was too long as I planned it, even after editting out significant portions, so I am instead breaking the videos into three parts. The first is this one which is an overview of the oscilloscope. The second will go over making measurements. The third will go over transferring the data to the computer. That's all for today, go out and make it a great one! 10 of 15

11 Oscilloscope Demonstration Transcript Since I'm out filming on location, I might as well share some places with you. This is one of the views I frequently get while out running. That is Blue Mound out there in the background. If you happen to see this view, you are close enough to my home to stop by and say hi. Turning to the task at hand, this video is going to go through demonstrations of how to perform some basic measurements using the oscilloscope. To demonstrate the functionality of the oscilloscope I am going to connect the oscilloscope to the function generator through a resistive- capacitive circuit. This will allow us to see most of the functionality we need to understand for the oscilloscope. To do this I am going to use BNC to micro clip connectors. These connectors have one end which is a BNC connector and another and which are microclips, hence the name. This allows us to connect into circuits wherever we want. When connecting BNC to microclip connectors, it is very important that all of the black leads from the microclips are connected to the same node on the circuit. That is because the black microclips are connected to earth ground. Since earth ground is our absolute reference for electrical signals, wherever I connect one of the black probes that point will be grounded or at zero volts, regardless of whatever waveform should be present. I m using a one kiloohm resistor and a one nanofarad capacitor in series for this demonstration. I ll first connect the output of the function generator across the series combination. This will serve as an input for the circuit. I ll then connect channel one of the oscilloscope to the same points. This will give us a picture of our input on the oscilloscope. Finally, I ll connect channel two of the oscilloscope across the capacitor so that we can observe the changes the circuit makes to our signal. I ll begin by adjusting the function generator to output a 10 khz one volt peak- to- peak signal. This produces a display on the oscilloscope which basically tells us nothing. From all we know about the signal, however we can adjust the oscilloscope so that we can see the waveforms. A 10 khz sine wave has a period of 100 microseconds. So, for us to see waveforms on the oscilloscope, we will have to adjust the seconds per division so that the full screen displays slightly more than 100 microseconds for us to see at least one full waveform. We can also adjust the volts per division to allow the display to show a one volt peak- to- peak signal, which if you watched the function generator video you know will actually show up on the oscilloscope as a two volt peak to peak signal and that has to do with the output resistance of the function generator. So now the display of the oscilloscope is set up so that the voltage display on both channels one and two is set to 500 millivolts per division and the time is set to 25 microseconds per division and we can see at least two full cycles of our wave forms. I can adjust where these waveforms are relative to each other using the position knobs for channels one and two. 11 of 15

12 If I press the channel one menu button we see the menu on the right- hand side of the screen changes. The top menu item is called coupling. The options for coupling are: DC, AC, and ground. Most often, when we are looking at circuits built on a breadboard, we want this to be set to DC. AC coupling filters out any DC component there may be with the signal and ground obviously makes that input zero. Below the coupling, there s something labeled BW limit. BW stands for bandwidth. This buttons has two options of a on or off. If the band with limiting is on, high frequency signals are filtered out. The volts per division menu item allows us to either make fine adjustments to the volts per division for the channel. Most of the time, we will not touch this. The probe of menu item allows us to adjust for different types of probes that we can use with an oscilloscope. With BNC to micro clip connectors, the 1X option is correct. There are more advanced probes that we can use with an oscilloscope that will require the 10X, 100X or 1000X settings. The last button is the invert button which will allow us to invert the waveform if we desire. The channel two button brings up the same exact options for channel two. In between the channel one and channel two buttons there is a math button. The math button will allow us to do some mathematical operations on our signals. For example, we could subtract or add the waveforms from channel one and two together. One of the reasons we may want to do this is, since the ground probes are absolute ground, if we want to know the voltage difference between two points in our circuit that are not connected to ground, subtracting the signals may be our only option. Another math option we have is the FFT or fast Fourier transform. The fast Fourier transform of the signal allows us to see what frequency components are present in the waveform. In this case, since we re looking at a sine wave output from a function generator, we see one peak on the left- hand side of the display and a bunch in noise to the right of it. This is because the waveform is almost a pure sine wave. Now I will press the measure button. The measure button changes the right- hand of the display to show a variety of measurements that the oscilloscope can perform. The top menu button allows us to select source or type. Source allows us to select which channel the measurement is taken from and if source is selected and I press any of the buttons next to the menu items, we see the channel changes from 1 to 2. If I press the top button so that type is selected, then we can change through the different types of measurements the oscilloscope can perform. I will cycle through these measurements for channel one. The oscilloscope can display the peak to peak value of the waveform, the rms value of the waveform, the rise time, the fall time, the positive width which is the width that the signal is high, the negative width which is the width that the signal is low, to no measurement, to the frequency, the period, the mean value, or back to the peak to peak value of the waveform. For any of the measure functions to work at least one entire waveform must be on the screen and of the entire waveform must be shown on the screen. If I adjust the volts per division so that the top of the waveform is off the top of the screen, a question mark appears on the peak- to- peak voltage. 12 of 15

13 This means the oscilloscope does not know what the peak to peak value is. Likewise if a full waveform is not displayed on the screen, the frequency measurements will come up as uncertain. The button below the measure button is the cursor button. The cursor button allows us to manually make measurements we want to make. There are two types of cursors that we can use, voltage cursors, and time cursors. When time cursors are selected, we see two vertical lines are present on the screen of the oscilloscope. The position of those time cursors is controlled by the position knobs on the vertical display so I can move the cursors anywhere I want on the horizontal axis. I can, for example, position the cursors on two subsequent peaks of a single waveform and in the delta section of the display, the difference between those two time cursors are shown along with the frequency that corresponds to that period. If I adjust the input frequency to 100 khz another purpose of the time cursors can be demonstrated. That would be to determine the phase shift between two waveforms. This is why I chose a resistive capacitive circuit for demonstration purposes. When the sine wave is input to resistive capacitive circuit, the waveform across the capacitor is shifted in time relative to the input. I can use of the cursor function to measure how big of a time shift has occurred. If I position the two waves to have the same zero crossing, I can put one of the cursors on the input wave and the other cursor at the zero crossing of the output wave and we see the shift in time of nearly one microsecond in this case is displayed. From this information, if I wanted to, I could then calculate something called the phase shift between these two waveforms. That may or may not have meaning to you right now but as you go through your introductory circuits courses it will have meaning to you. I could also switch the cursors to voltage cursors. This might allow me to see how much of a voltage change there is between two waveforms in very precise terms. One advantage that cursor measurements have over using the oscilloscope is that the cursor functions do not need to have a full waveform displayed on the screen. So if I wanted to zoom in on the waves to see a very precise measurement using the cursor functions, I can do that. Let s go over the basics of the trigger menu. On the right hand side of the oscilloscope there is a section regarding the trigger. The top knob refers to trigger level. As I turn the knob, there is an arrow that goes up and down on the right- hand side of the screen and that tells the oscilloscope at what voltage level to grab the waveform. If I adjust the trigger level above the actual waveform the oscilloscope cannot grab onto the wave and the display becomes unstable. To grab one of the waves again I simply need to adjust the trigger level into the middle of the wave. The trigger menu button brings up several options for the trigger. I will not go through them all but let s take a look at the coupling. Sometimes when we are trying to look at a signal there will be a lot of noise present and it will be difficult to obtain a stable waveform. By adjusting the coupling on the trigger very often this can be corrected. The options we have for coupling are DC coupling, noise reject 13 of 15

14 (this will provide a general filter for noise in a signal), high frequency reject will get rid of the high frequency components of the wave, low frequency reject will get rid of low frequency noise such as the 60 Hz signal that we often pick off from the electricity in the room, AC coupling will block out any DC portions of the signal, and then we are back to DC coupling. If were having trouble triggering a signal very often just cycling through these options will correct our problem. If we are using a function generator to generate our signal and we are having a lot of trouble getting our signals trigger, we can use the sync output of the function generator with the external trigger option on the oscilloscope. For that I will use a BNC cable to connect the sync to the external trigger. To use the external trigger, I go to the button next to trigger source on the oscilloscope screen and select the external. This allows the oscilloscope to trigger off of the very stable square wave the sync of the function generator outputs and renders any distortion of the output of the function generator irrelevant. Now you should be able to, at least, muddle through a few measurements using the oscilloscope. Like anything, it will take some time and practice to feel comfortable and proficient in the use of the scope. You may already be able to imagine that once you do, it will be a great asset to your laboratory analysis toolbox. That s all for today, go out and make it a great one! Oscilloscope Wintek32 Interface Transcript By now you should know the basic operation of an oscilloscope, how to connect your circuit to the oscilloscope, and how to perform various measurements using the oscilloscope. Sometimes, however, that is not enough and you need to document your results. This is especially true in school where the untrusting professors often ask you to show your actual measurements as part of a laboratory project report. For some reason, My circuit worked, take my word for it just isn t good enough for them. Later, if you are working as an engineer, you may not need this level of documentation all the time only because if you fudge your data it will be very obvious during testing and verification. If you get caught massaging your data, by the way, you will not be an engineer for long, nor should you be. If this seems strange to you, take a read through the NSPE Code of Ethics for Engineers. Don t forget to look up the hard words (vocabulary is not a traditional strongpoint of engineers). Back to today s topic, getting data from the oscilloscope to your computer. 14 of 15

15 Now let s go over how to download an image from the oscilloscope to the computer. To do this I am going to open Wintek32 from the desktop of the computer. I m also going to open up Microsoft Word. We see on the Wintek32 interface that it is listening on com1 at 9600 baud. BAUD is a data rate for RS232 communication. On the Wintek32 interface we see that we can choose to either save an image to the clipboard or to the disk. If I select disk and I need to go into the file menu under target file select a directory and a file name. I am just going to save the files to the clipboard, which is just in the memory of the computer. Once Wintek32 is open on the desktop I will press run/stop on the oscilloscope. This ensures that the image I want to capture will not change even if I were to bump the circuit we are measuring. Once the RUN/STOP button is pressed, I hit hard copy and the computer shows that it is receiving information. RS232 communication is slow. Downloading images can take a while. I ll speed this up. Once the image is done downloading, it will display on Wintek32 that the images posted to the clipboard. To see the image, I can click into Microsoft Word and paste the image. This can be done by right clicking and selecting paste, or by using the keyboard shortcut Control- V. Once we have downloaded the image into our document and saved it, we should remember to push RUN/STOP on the oscilloscope again so that we can take a new measurement. That is the last piece the three video series covering the basic functionality and use of the oscilloscope. There are more advanced oscilloscopes and more advanced measurements that can be done, but you should have what you need for your introductory classes. That s all for today, go out and make it a great one. 15 of 15