This document provides information about three key laboratory instruments: the cathode ray oscilloscope (CRO), function generator, and digital multimeter. It describes the CRO in detail, including that it consists of a cathode ray tube, controlling circuit, and power supply. The cathode ray tube uses an electron beam and deflection plates to display voltage and current waveforms on its screen. The function generator generates electrical sine, square and triangular waves using oscillator circuits. The digital multimeter measures voltage, current, resistance and other electrical properties digitally.

1. D.S.Vidyasagar
Understanding
INSTRUMENTS

2. Contents
This chapter covers three most
important laboratory
instruments.
• Cathode Ray Oscilloscope
• Function Generator
• Digital Multimeter

3. Cathode Ray Oscilloscope
A cathode ray oscilloscope
is abbreviated as CRO. It
is a versatile lab
instrument. It can measure
ac/dc voltage, ac/dc
current, resistance,
frequency, wavelength,

4. A prototype of CRO

5. What is inside a CRO?
The CRO consists
of three main
sections:
• Cathode ray tube
• Controlling circuit
• Power supply

6. What is CRT?
• The CRT is heart of CRO.
• It is used to display different types of
waveforms or patterns on its screen.
• The waveforms or patterns are drawn with
the help of high speed electron beam on the
electron sensitive fluorescent screen by
deflecting the beam horizontally and vertically.

7. Inside the CRT

8. Schematic of CRT
accelerating
anodes
focusing
anode
control
grid
cathod
filament
sealing
base
connectingpins
e-beam
vertical
plates
hor. def.
plates
aquadag
coating
phosphor
coating
vacuum lighted
spotglass tube
screen

9. Details of CRT
• The filament heats up the cathode.
• Cathode emits large number of electrons.
• Control grid covers cathode. It has a tiny
hole on its surface.
• So all the electrons come out of this hole
and produce diverged beam due to mutual
repulsion.

10. Electron Gun Assembly
Control grid Cathode

11. Details of CRT…
• The 3 accelerating anodes are connected
to high-to-low positive voltage in reducing
order from base to screen.
• Due to gaps in between the anodes,
electrostatic lens system is produced within
accelerating anodes.

12. Details of CRT…
Screen
control grid
cathode
diverged
electron bean High +ve
voltage
High +ve
voltageFocus
adjustment
Pre-accelerating
anode
Second accelerating
anodeFocusing anode

13. Deflection Systems in CRT
 The electron beam
is deflected using
electric field applied
across the two pairs
of deflection plates.
 The electron beam
is deflected using
magnetic field which
is created using
yoke system.
Electrostatic Deflection
System
Magnetic Deflection System

14. Electrostatic Deflection System
Two pairs of
deflection
plates used
in this
system.
They are:
Vertical
deflection
plates
Horizontal
deflection
plates
distance
(d)

screen
parabolic
path
straight
path
vertical
deflection
plates
D
P
P
(+)
(-) electric field
(flux)

15. Magnetic Deflection System
Two pairs of
deflection
coils are
used in this
system.
They are
fitted on the
neck of CRT
from outside.
It is called as
YOKE.
deflection
coilselectron gun
assembly
picture tube
screen
deflection
of beam

16. Applications
 Used in CRO
 Used in ECG
 Used in earthquake
monitoring system
 The electron beam
is deflected using
magnetic field which
is created using
yoke system.
Electrostatic Deflection
System
Magnetic Deflection System

17. Why it is called yoke…?

18. Block
Diagram of

19. Applications of CRO
 AC/DC voltage measurement
 AC/DC current measurement (indirect
method)
 Frequency and Phase measurement
using Lissajou’s patterns

20. DC Voltage Measurement

21. AC Voltage Measurement

22. Frequency Measurement
(Direct Method)

23. Lissjou’s Patterns
Frequency measurement

24. More Lissjou’s Patterns
Frequency measurement

25. More Lissajou’s Patterns
Such pattern
may obtain
during relative
frequency
measurement

26. Frequency Measurement
(Relative Method)

27. Lissjou’s Patterns
Phase measurement
b
a
Phase difference
0 or 360
0 0
Phase difference
90 or 270
0 0
Phase difference
180
0
(a) (b) (c)
Special cases of phase difference between the waveforms

28. Function Generator
It generates different types
of waveforms electrically. It
uses oscillator circuits to
generate sine wave, square
wave and triangular wave,
etc.

29. How it works…?

30. Digital Multimeter
It generates different types of
waveforms electrically. It uses
oscillator circuits to generate
sine wave, square wave and
triangular wave, etc.

31. How it works…?

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Designed by: D.S.Vidyasagar