1. Introduction to the Oscilloscope Engr. Annalyn soria Lecturer

2. Electrical Signal How do we classify the signals that we measure?

3. Electrical Signals: D.C. Signal A direct current or D.C. signal is one that only flows in a single direction. Typical Sources Batteries Agilent Power Supply in the ECE labs X=TIME (seconds) Y=VOLTAGE (volts) 5 10 15 20 5 2.5 -2.5 -5 What is the value at 5 Seconds? 20 Seconds?

4. Electrical Signal: A.C. Signal A.C. or Alternating Current signals are ones that change direction over time. As time increases our voltage fluctuates up and down. Typical Sources Function Generators Electrical Outlets in Buildings So at time=2.5s, what is the voltage? And again at 10seconds?...15 seconds? X=TIME (seconds) Y=VOLTAGE (volts) 5 10 15 20 5 2.5 -2.5 -5

5. Electrical Signals DC Signals are usually characterized by their voltage. AC Signals are characterized by their: Shape Frequency (Cycles Per Second) Period (Seconds Per Cycle) Amplitude

6. Common Lab Equipment

7. Oscilloscope The oscilloscope is basically a graph-displaying device It draws a graph of an electrical signal. In most applications the graph shows how signals change over time: the vertical (Y) axis represents voltage the horizontal (X) axis represents time.

8. Oscilloscope

9. Cathode Ray Tubes Variation in potential difference (voltage) placed on plates causes electron beam to bend different amounts. “Sweep” refers to refreshing repeatedly at a fixed rate.

10. What is the purpose of an oscilloscope The purpose of an oscilloscope is to measure a voltage that changes with time and show it in a graphical format 1)Here is the oscilloscope in our lab -Notice the X-Y axes 2) Here is our alternating voltage signal from before 3) If we measure our signal with the scope, it would look like this!

11. Scope (Con’t) This simple graph can tell you many things about a signal: You can determine the time and voltage values of a signal. You can calculate the frequency of an oscillating signal. You can see the "moving parts" of a circuit represented by the signal. You can tell if a malfunctioning component is distorting the signal. You can find out how much of a signal is direct current (DC) or alternating current (AC). You can tell how much of the signal is noise and whether the noise is changing with time.

12. What are the major components? Display Screen Displays an input signal with respect to time. Control Panel Adjusts how the input signal is displayed.

13. What do we now know about the scope? What must the X-Axis represent? What must the Y-Axis represent? TIME VOLTAGE So…what do the dials do?

14. Oscilloscope: Screen Notice that the screen has ruled divisions both horizontally and vertically. The axes can be scaled, for example… If each vertical division is worth 5 seconds, what time is represented by this point? If each horizontal line is worth 1 volt, what voltage is represented by this point?

15. Oscilloscope: Control Panel The section to the right of the screen contains the controls necessary to adjust how the waveform is displayed on the screen. The controls allow you to alter the sweep time, amplitude, and triggering method. (Note, these topics will be discussed later)

16. Oscilloscope: Input Channels How do we get the voltage into the scope? This area is broken into two parts Left Half for Channel 1 (X) Right Half for Channel 2 (Y) In the center is a switch that determines which channel will serve as the input to the scope: 1, 2, Dual or Add. Why would we want more than 1 channel? Channel 1 Channel 2

17. Triggering Telling the Oscilloscope when to capture information.

18. Triggering Electric signals change much faster than we can observe. To view a meaningful version of the signal, we must tell the Oscilloscope when to refresh the display. We accomplish this by setting a Triggering Level.

19. Triggering Without Triggering With Triggering

20. Triggering We want to tell the oscilliscope when it is the best time for it to “refresh” the display In our wave below, we tell the scope to “trigger” or ‘capture’ the signal when it is going upward AND hits 2.0Volts Going up! AND When at 2.0 Volts on our waveform! SO, ‘trigger’ condition is: When we’re

21. Waveform shapes tell you a great deal about a signal

22. If a signal repeats, it has a frequency. The frequency is measured in Hertz (Hz) and equals the number of times the signal repeats itself in one second

23. Voltage, Current, & Phase

24. Performance Terms Bandwidth The bandwidth specification tells you the frequency range the oscilloscope accurately measures. Rise Time Rise time may be a more appropriate performance consideration when you expect to measure pulses and steps. An oscilloscope cannot accurately display pulses with rise times faster than the specified rise time of the oscilloscope. Vertical Sensitivity The vertical sensitivity indicates how much the vertical amplifier can amplify a weak signal. Vertical sensitivity is usually given in millivolts (mV) per division. Sweep Speed For analog oscilloscopes, this specification indicates how fast the trace can sweep across the screen, allowing you to see fine details. The fastest sweep speed of an oscilloscope is usually given in nanoseconds/div. Gain Accuracy The gain accuracy indicates how accurately the vertical system attenuates or amplifies a signal. Time Base or Horizontal Accuracy The time base or horizontal accuracy indicates how accurately the horizontal system displays the timing of a signal. Sample Rate On digital oscilloscopes, the sampling rate indicates how many samples per second the ADC can acquire. Maximum sample rates are usually given in megasamples per second (MS/s). The faster the oscilloscope can sample, the more accurately it can represent fine details in a fast signal.. ADC Resolution (Or Vertical Resolution) The resolution, in bits, of the ADC indicates how precisely it can turn input voltages into digital values. Record Length The record length of a digital oscilloscope indicates how many waveform points the oscilloscope is able to acquire for one waveform record.

25. Grounding Proper grounding is an important step when setting up to take measurements. Properly grounding the oscilloscope protects you from a hazardous shock and protects your circuits from damage. Grounding the oscilloscope is necessary for safety. If a high voltage contacts the case of an ungrounded oscilloscope, any part of the case, including knobs that appear insulated, it can give you a shock. However, with a properly grounded oscilloscope, the current travels through the grounding path to earth ground rather than through you to earth ground. To ground the oscilloscope means to connect it to an electrically neutral reference point (such as earth ground). Ground your oscilloscope by plugging its three-pronged power cord into an outlet grounded to earth ground. Grounding is also necessary for taking accurate measurements with your oscilloscope. The oscilloscope needs to share the same ground as any circuits you are testing. Some oscilloscopes do not require the separate connection to earth ground. These oscilloscopes have insulated cases and controls, which keeps any possible shock hazard away from the user.

26. Scope Probes Most passive probes have some degree of attenuation factor, such as 10X, 100X, and so on. By convention, attenuation factors, such as for the 10X attenuator probe, have the X after the factor. In contrast, magnification factors like X10 have the X first

27. Vertical Controls Position and Volts per Division The vertical position control lets you move the waveform up or down to exactly where you want it on the screen. The volts per division (usually written volts/div) setting varies the size of the waveform on the screen. A good general purpose oscilloscope can accurately display signal levels from about 4 millivolts to 40 volts. Often the volts/div scale has either a variable gain or a fine gain control for scaling a displayed signal to a certain number of divisions.

28. Horizontal Controls Position and Seconds per Division The horizontal position control moves the waveform from left and right to exactly where you want it on the screen. The seconds per division (usually written as sec/div) setting lets you select the rate at which the waveform is drawn across the screen (also known as the time base setting or sweep speed). This setting is a scale factor. For example, if the setting is 1 ms, each horizontal division represents 1 ms and the total screen width represents 10 ms (ten divisions). Changing the sec/div setting lets you look at longer or shorter time intervals of the input signal.

29. Trigger Position The trigger position control may be located in the horizontal control section of your oscilloscope. It actually represents "the horizontal position of the trigger in the waveform record." Horizontal trigger position control is only available on digital oscilloscopes. Varying the horizontal trigger position allows you to capture what a signal did before a trigger event (called pretrigger viewing). Digital oscilloscopes can provide pretrigger viewing because they constantly process the input signal whether a trigger has been received or not. A steady stream of data flows through the oscilloscope; the trigger merely tells the oscilloscope to save the present data in memory. In contrast, analog oscilloscopes only display the signal after receiving the trigger.

30. Pulse and Rise Time Measurements

31. Signa Generator An electronic instrument that generates various waveforms such as Sine wave Square wave Pulse trains Sawtooth The amplitude, DC offset, frequency are adjustable.

32. Signal Generator A signal generator is an electronic device that generates repeating or non-repeating electronic signals in either the analog or the digital domain.  It is generally used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices, though it often has artistic uses as well. Types: The AF oscillators are divided into two types. 1. Fixed frequency AF oscillator 2. Variable frequency AF oscillator.