The Oscilloscope

1. The Oscilloscope For the measurement of voltage: AC and DC

2. The Oscilloscope It is an instrument used to measure voltage across two points connected to its Y A entry and M mass terminals. The symbol of Y A is The symbol of Mass M is The Mass M acts like the com of a multimeter The oscilloscope allows us to visualize the voltage as if it were a graph of Voltage versus time.

3. What it looks like

4. Two control knobs Vertical sensitivity S v Volts/div or m Volts/div Horizontal sensitivity S h (or time base V b Time/div s, ms, or µs /div This knob is used only in AC voltage mearsurement

5. The Screen

6. What it does The oscilloscope ‘plots’ and displays a graph of variation of voltage across the connected points, as time passes. The display of an oscilloscope is similar to: U (V) t (s)

7. At the start The oscilloscope is zeroed, such that the horizontal luminous line appears at the base position, in the center.

8. Then The terminals of the oscilloscope are connected across points in a circuit. The luminous line is noticed to displace. The number of divisions between the luminous line and the base position is referred to as y.

9. Oscilloscope- DC voltage A sample question 1 Assuming the oscilloscope display has been properly "zeroed" and the vertical sensitivity is set to 5 volts per division, determine the voltage of the battery.

10. From the screen we see that the signal is a flat horizontal line. It was displace upwards. The luminous line is 1.3 divisions above the base horizontal position. Oscilloscope- DC voltage A sample question- solved => y = 1.3 div

11. Oscilloscope- DC voltage A sample question- solved => y = 1.3 div And given that S v = 5 V/div U PN = Sv x y = 5 V/div x 1.3div = 6.5 V

12. A sample question 2- DC voltage The YA and M terminals of an oscilloscope are connected to points A and B across a lamp in a closed circuit. The vertical sensitivity was set at 2V/div. The adjacent display appeared on the screen. 1- Determine the voltage across the lamp. 2- If the connections were switched: a- What voltage would be measured then. Give its value. b- How would the display differ?

13. Downward displacement of the luminous line- question 3 1- What causes a down-ward displacement of the luminous line? 2- Is the value of y positive or negative in this case? 3- What can you say about the sign of the measured voltage? 4- What can you deduce about the connections in the shown figure?

14. Downward displacement of the luminous line- question 3 The M terminal of the oscilloscope is to the side of the positive terminal of DC source, thus in this case we are measuring U NP The measured voltage is negative, and so is the value of y (number of divisions the luminous line was displaced by)

15. In general If the measured voltage is negative, then the value of y (number of divisions the luminous line was displaced by) is also negative, and the luminous line is displayed below the base horizontal position: U = y x Sv If U is negative due to connection Then y appears below the base horizontal position and is negative in value. (V) (div) (V/div)

16. DC versus AC voltages A DC source sends into a circuit a current that flows in one direction. The DC voltage remains constant in value and in sign. Thus this voltage is known as Direct (one direction, one sign) and continuous (one value) The current resulting from an AC source doesn’t have one direction, its charged particles vibrate and collide. The signs of the terminals alternate many times per second. Such voltage is said to be alternating (in sign) and variable( in value)

17. DC versus AC voltage: Oscilloscope displays Direct and continuous voltage ( Direction ) ( Value ) Alternating and variable voltage ( Direction ) ( Value ) + - + - +

18. Thank you  Next: exercises 12 and 13 on page 68 in the book.