by: CSE STUDY MATERIALS
Objective
To get familiar with the functionalities and uses of the:
The cathode ray oscilloscope. This versatile
instrument was developed by Brown in 1897 from the cathode ray tube. It has
many uses, including voltage measurement, observation of wave
forms, frequency comparison and time measurement. Figure 1 is a simplified diagram
of a cathode ray oscilloscope.
The cathode ray oscilloscope is an
instrument which we use in laboratory to display measure and analyze various
waveforms of various electrical and electronic circuits.
Actually, cathode ray oscilloscope is very fast X-Y plotters
that can display an input signal versus time or another signal.
The cathode-ray oscilloscope (CRO) is a common
laboratory instrument that provides accurate time and amplitude measurements of
voltage signals over a wide range of frequencies.
Figure 1:
A Brief diagram of CRO
A digital multimeter (DMM) is a test tool
used to measure two or more electrical values—principally voltage (volts),
current (amps) and resistance (ohms).
A function generator is usually a piece of
electronic test equipment or software used to generate different types of
electrical waveforms over a wide range of frequencies. Some of the most common
waveforms produced by the function generator are the sine, square,
triangular and sawtooth shapes.
There are two types of function generator, one is inside the
Cathode Ray Oscilloscope and the second one, we connect that from the outside
of the oscilloscope.
Figure 2
Solderless breadboard with 400 connection
points. Electrical equivalent printed circuit board (PCB) of the
above solderless breadboard. A breadboard is a
construction base for prototyping of electronics.
Knobs and buttons in CRO
- Focus: A type of knob, used to focus the screen for the purpose to gain the clear view of the wave
- Intensity: Knob used to control the brightness, dullness of the waves.
- Triger: Used for the reappearance of the wave.
- Chock: To find the phase difference.
- Ground: Used to ground the Electric circuit.
- External Knobs: other many external knobs are also commonly used with the CRO like in the function generator etc. thay are also used to control the time and frequency of the waves like volt/div and time/div knobs.
The Frequency of
a wave is the number of times per second that a wave repeats its shape.
We cannot directly measure the frequency on the oscilloscope, but we can
measure a closely related parameter called Timeperiod.
Figure 3
Adjust the waves at a particular space that it covers some
calculatable boxes or divisions vertically and horizontally.
As indicated in the image above, one cycle is completed in 2
horizontal grid divisions. As indicated in the bottom of the screen, here
the knob of (time/div) set to 1ms.
Timeperiod / dividion
= 1ms (div = 2)
Timeperiod = (1*2) ms
T = 2ms
Now calculating the frequency:
Frequency = 1 / Timeperiod
f = (1 / 2) *(m =
1000)
f = 500 Hz
From the fig.3, we will calculate the amplitude the wave.
There would be a knob of (volt / division) just like in the case of (time /
division), we will figure out the values on it, then:
Volt / div = 0.1
Volt = 0.1 * 5 = 0.5
Amplitude = 0.5
|
S.no
|
Amplitude
(volt)
|
Frequency
(func. Gen.)
|
Timeperiod
(CRO)
|
Frequency
(CRO)
|
Error (%)
|
|
1
|
0.6
|
500 Hz
|
2 ms
|
500 Hz
|
0%
|
|
2
|
0.4
|
2000
Hz
|
0.4
ms
|
2500
Hz
|
20%
|
|
3
|
0.4
|
300 Hz
|
3 ms
|
333 Hz
|
10%
|
|
4
|
0.6
|
1000
Hz
|
0.8
ms
|
1250
Hz
|
20%
|
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