Introduction to the Tektronix TDS210 Oscilloscope
Contents
1. e Look at each of the waveforms available from the function generator square sine and triangle Try out the frequency and voltage controls and explain how they work Adjust the function gen erator s frequency to about 1 kHz e Display both scope channels with one channel looking at the output of the function generator and the other looking at the scope s calibrator signal Make sure the vertical sensitivity and offset are adjusted for each channel so that the signal trace is visible e What do you see on the screen if you trigger on channel 1 On channe12 e What do you see if neither channel causes triggering for example if the trigger threshold is set too high or too low e How does this depend on whether you select normal or auto trigger mode Why If you find this confusing be sure to ask for help or study the oscilloscope manual more carefully 1 3 6 Additional features The TDS210 has many more features than the ones we ve described so far Particularly useful are the digital measurement features Push the MEASURE button to program these You can use them to meas ure the amplitude period and frequency of a signal The scope does not measure amplitude directly How then can you derive the amplitude from something the scope does measure e Using the measurement features determine the amplitude frequency and period of a waveform of your choice from the function generator You can also use the on screen cursor2. LEVEL knob sets the threshold voltage for triggering You can select whether triggering occurs when the threshold voltage is crossed from below rising edge triggering or from above falling edge triggering using the trigger menu or for some scope models using trigger control knobs and switches You can also select the signal source for the triggering circuitry to be channel 1 channel 2 an external trigger signal or the 120 V AC power line and control various other triggering features as well Since setting up the trigger can be tricky the TDS210 provides an automatic setup feature via the AUTOSET button which can lock in or almost any repetitive signal presented at the input and adjust the voltage sensitivity and offset the time sensitivity and the triggering to produce a stable display e After getting a stable display of the calibrator signal adjust the LEVEL knob in each direction until the scope just barely stops triggering What is the range of trigger level that gives stable triggering on the calibrator signal How does it compare with the amplitude of the calibrator waveform Does this make sense Explain Next connect the scope probe to the breadboard s function generator you can do this by inserting a wire into the appropriate breadboard socket and grabbing the other end of the wire with the scope probe s grabber The function generator s amplitude and frequency are adjusted by means of sliders and slide switches
3. probe can distort a signal The manufacturer therefore provides a compensation adjustment screw which needs to be tuned for minimum distortion The screw is usually located on the assembly that connects the probe to the scope or occasionally on the tip assembly e Display the calibrator square wave signal on the scope If the signal looks distorted i e not square carefully adjust the probe compensation using a small screwdriver If you have trouble achieving a stable display try AUTOSET e Check your other probe Make sure that both probes work are properly compensated and have equal calibrations Sketch the observed waveform Consult your oscilloscope user manual for more information about carrying out a probe test Note that each probe also has an alligator clip sometimes referred to as the reference lead or ground clip This connects to the shield of the coaxial cable It is useful for reducing noise when look ing at high frequency time intervals of order nanoseconds or low voltage signals Since it is connected directly to the scope s case which is grounded via the third prong of the AC power plug it must never be allowed to touch a point in a circuit other than ground Otherwise you will create a short circuit by con necting multiple points to ground which could damage circuit components This is no trouble if you are measuring a voltage with respect to ground But if you want to measure a voltage dro
4. Introduction to the Tektronix TDS210 Oscilloscope From Daniel M Kaplan and Christopher G White Hands On Electronics Cambridge University Press Cambridge 2003 1 3 Oscilloscope With its many switches and knobs a modern oscilloscope can easily intimidate the faint of heart yet the scope is an essential tool for electronics troubleshooting and you must become familiar with it Ac cordingly the rest of this laboratory session will be devoted to becoming acquainted with such an instru ment and seeing some of the things it can do The oscilloscope we use is the Tektronix TDS210 illustrated in Fig 1 4 If you don t have a TDS210 any dual trace oscilloscope analog or digital can be used for these labs as long as the band width is high enough ideally 30 MHz or higher While the description below may not correspond ex actly to your scope with careful study of its manual you should be able to figure out how to use your scope to carry out these exercises The TDS210 is not entirely as it appears In the past you may have used an oscilloscope that dis played voltage as a function of time on a cathode ray tube CRT While the TDS210 can perform a simi lar function it does not contain a CRT part of the reason it is so light and compact HORIZONTAL AUTOSET Seconds per MEASURE CONTROLS Division CURSOR TRIGGER LEVEL TRIGGER MENU Volts per Division Horizontal and Vertical Info Trigger Level SEC DIV CALIBRA
5. TION MENU r VOLTS DIV CONTACT POINT OPTION VERTGAL BUTTONS CONTROLS Figure 1 Illustration of the Tektronix TDS210 digital oscilloscope The basic features to be used in this tuto rial are marked Note and remember the location of the AUTOSET button when all else fails try autoset Until the 1990s most oscilloscopes were purely analog devices an input voltage passed through an amplifier and was applied to the deflection plates of a CRT to control the position of the electron beam The position of the beam was thus a direct analog of the input voltage In the past few years analog scopes have been largely superseded by digital devices such as the TDS210 although low end analog scopes are still in common use for TV repair etc A digital scope operates on the same principle as a digital music recorder In a digital scope the input signal is sampled digitized and stored in memory The digitized signal can then be displayed on a com puter screen One of your first objectives will be to set up the scope to do some of the things for which you may al ready have used simpler scopes After that you can learn about multiple traces and triggering In order to have something to look at on the scope you can use your breadboard s built in function generator a de vice capable of producing square waves sinusoidal waves and triangular waves of adjustable amplitude and frequency But start by using the built in calibrator signal pro
6. p between two points in a circuit neither of which is at ground first observe one point with the probe and then the other The difference between the two measurements is the voltage across the element During this process the reference lead should remain firmly attached to ground and should not be moved Alternatively you can use two probes and configure the scope to subtract one input from the other Warning A short circuit will occur if the probe s reference lead is connected anywhere other than ground 1 3 2 Display Your oscilloscope user s manual will explain the information displayed on the scope s screen Record the various settings timebase calibration vertical scale factors etc e Explain briefly the various pieces of information displayed around the edges of the screen The following exercises will give you practice in understanding the various settings For each you should study the description in your oscilloscope user s manual The description below is specific to the TDS210 if you have a different model your manual will explain the corresponding settings for your scope 1 3 3 Vertical controls There is a set of vertical controls for each channel see Fig 1 4 These adjust the sensitivity volts per vertical division on the screen and offset the vertical position on the screen that corresponds to zero volts The CH Il and CH 2 menu buttons can be used to turn the display of each channel on or off
7. s to make measurements e Use the cursors to measure the half period of the signal you just measured e Explain how you made these measurements and what your results were A feature that comes in particularly useful on occasion is signal averaging this is programmed via the ACQUIRE button and allows noise which tends to be random in time to be suppressed relative to signal which is usually periodic
8. they also select which control settings are programmed by the push buttons just to the right of the screen e Display a waveform from the calibrator on channel 1 What happens when you adjust the POSITION knob The VOLTS DIV knob 1 3 4 Horizontal sweep To the right of the vertical controls are the horizontal controls see Fig 1 4 Normally the scope dis plays voltage on the vertical axis and time on the horizontal axis The SEC DIV knob sets the sensitivity of the horizontal axis i e the interval of time per horizontal division on the screen The POSITION knob moves the image horizontally on the screen e How many periods of the square wave are you displaying on the screen How many divisions are there per period What time interval corresponds to a horizontal division Explain how these ob servations are consistent with the known period of the calibrator signal e Adjust the SEC DIV knob to display a larger number of periods Now what is the time per divi sion How many divisions are there per period 1 3 5 Triggering Triggering is probably the most complicated function performed by the scope To create a stable im age of a repetitive waveform the scope must trigger its display at a particular voltage known as the trig ger threshold The display is synchronized whenever the input signal crosses that voltage so that many images of the signal occurring one after another can be superimposed in the same place on the screen The
9. vided by the scope on a metal contact labeled probe comp or something similar often located near the lower right hand corner of the display screen Note that a leg folds down from the bottom of the scope near the front face This adjusts the viewing angle for greater comfort when you are seated at a workbench so we recommend that you use it 1 3 1 Probes and probe test Oscilloscopes come with probes cables that have a coaxial connector similar to that used for cable TV on one end for connecting to the scope and a special tip on the other for connecting to any desired point in the circuit to be tested To increase the scope s input impedance and affect the circuit under test as little as possible we generally use a 10X attenuating probe which has circuitry inside that divides the signal voltage by ten Some scopes sense the nature of the probe and automatically correct for this factor of ten others such as the TDS210 need to be told by the user what attenuation setting is in use As mentioned above your scope should also have a built in calibrator circuit that puts out a stan dard square wave you can use to test the probe see Fig 1 4 The probe s coaxial connector slips over the CH I or CH 2 input jack and turns clockwise to lock into place The probe tip has a spring loaded sheath that slides back allowing you to grab the calibrator signal contact with a metal hook or grabber An attenuating scope
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