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Explanation about the principal of working, construction & the circuitry of cathode ray oscilloscope


Posted Date: 07-May-2011  Last Updated:   Category: Education    
Author: Member Level: Gold    Points: 35


In this article I will be giving some basic information about the most commonly used engineering instrument cathode ray oscilloscope. We will discuss how it is used for the observation and study purposes of DC or AC waveform, what is its basic circuitry and how it performs the various numbers of tasks it is designed to do



Introduction to general principle of cathode ray oscilloscope


In this article we are going to have some introductory information about general functionality of a cathode ray oscilloscope that is an instrument used for communication study purposes, requirement of study of waveform of various type of signal, be it DC of AC, is performed. Generally it deals with electronic branch of science that involves very complex and integrated circuitry for operation. This way it becomes a complete system comprising of circuitry for performing various tasks like amplification of input weak signals, their calibration according to the scale for their representation upon the screen.
Cathode ray oscilloscope being a very useful and versatile can be used for measurement and analysis in laboratories of an electronic instrument. Not only measurements, it can also be used for study of many other electrical and electronic phenomenon and properties. Taking it to the most basic level it is actually a XY plotter that is capable of displaying an input signal against another signal or time, in most common case. There exists a spot that moves along the screen in response of an applied input signal, this spot is a luminous spot that appears because of staking of electron been over florescent screen. This beam is produced by the input applied voltage at the input section of the oscilloscope having negligible inertia effect with them. The beam is having relatively very low inertia when it is compared with metallic conductors which are used in other oscillators like Duddell's oscilloscope. This capability of cathode ray oscilloscope over other oscilloscopes makes it faster than them on the basis of their frequency acceptance for measurement.
A horizontal voltage, as input voltage, is used in this oscilloscope that is actually a voltage that is generated internally in it and termed as ramp voltage. This is the voltage which is responsible for movement of luminous spot across the screen in horizontal direction and in specified direction i.e. from left to right. On the other hand movement of spot along y direction is governed by applied input voltage in such a way that the spot moves up or down in accordance with applied input voltage and whose magnitude depends directly upon magnitude of testing signal. In this way this spot while moving from left to right actually traces the whole wave form of applied signal and makes it possible to observe an analyse the signal under test. When it becomes the case that the input signal repeats itself, then moving trace appears to be stationary upon the screen. In this way a mean of visualizing input signal in obtained with this type of oscilloscope. And it becomes such a tool in field of electrical and electronics that provides wide possibility of measurement and analysis of electrical properties and phenomenon. As CRO works upon application of voltage to it that may be obtained from a variety of sources. In this way if we apply some proper type of transducer and convert different physical quantities like velocity, acceleration, speed, pressure, poser consumed in circuits or power stations, movement of extra terrestrial and terrestrial bodies into their equivalent electrical form them it becomes possible to study them by visualizing their change and pattern that they follow with respect of time or any other parameter. They can also be used for the study of transient phenomenon, time varying quantities.
With a continuous advancement in technology they have been evolutions so far that now it is possible with them to measure the signal of frequency up to 1 GHz. There is arrangement of traditional features associated with them like:
  • Digital multi-meter
  • Counter
  • Additional amplifiers etc.

In this way it is perceived that they are continuously getting smarter and smarter with time. It can be even seen by the fact that some of them are controlled by microcontrollers. These are found to be capable of performing many different functions with the given input signal like:
  • Calculation of rise time
  • Calculation of pulse width
  • To display these quantities along with their concerned waveform

Such internal routine are available that acts as a guide for the user to make it user friendly. Now a day it has become possible to make such oscilloscope having IEEE 488 bus capabilities with that enables them to be a part of measurement test bed along with a control set at a distant location and reading being digitized and retrieved so that recording and analysis may be performed upon it.
As a traditional basis most of the oscilloscopes are monochromatic i.e. black and white that can plot the wave form in single colour. But now many coloured oscilloscopes are finding their place in market.

Use of oscillator in immerging technology


  1. Waveform analysis in communication system design.
  2. Output analysis designed electronic circuits and their response to wards different voltage and current inputs.
  3. In determination of time constant, phase shift, frequency, pulses width, and amplitude variations of the signal under test.
  4. Study of noise spectrum in received signals at the receiver section of communication systems.
  5. For study of wave propagation of in laboratories.
  6. For visualization of physical quantities after their conversion into proper electrical form so that the changes occurring over there may be observe and study may become even simpler.

Disadvantages of cathode ray oscilloscope


Although these are proven to be very useful by the virtue of their application in wave form analysis but still them come up with their own embedded limitations. Some of them can be summarized as followed:
  1. It is a very sensitive device and is often noise prone i.e. upon application small signals to them noise may enter in the system through open wiring, exposed metallic components and unprotected parts. So they require complete isolation from noise prone sources.
  2. When it comes to analyse very high frequency signals a general cathode ray oscilloscope becomes incapable to produce some reliable result because that much of variations are not supported by normal electronic components used in them.
  3. Very sudden changes cannot be observed with normal CRO, particularly when they are occurring at very high frequency because they occur for a very small instant of time and human eye remains incapable of observing them.
  4. Cathode ray oscilloscope cannot be used for study of high voltage signals and in order to study them they first need to be converted to low voltage, this puts a limiting mark upon application of these instruments.
  5. They are a lot of control terminals over the control panel that leads to a greater complexity of the device making it difficult to use.
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