All the engineers would be familiar with Cathode Ray Oscilloscope (CRO) but for those who are not, it is an electrical device which displays an input signal versus another signal. So, in this article we are going to give its brief introduction, with its important parts and its accessories.
What is Cathode Ray Oscilloscope – CRO
CRO stands for Cathode Ray Oscilloscope, earlier it was simply called Oscillo-graph. This instrument is seen in electrical laboratories. It is very versatile and useful instrument generally used for measurement and analysis of wave-forms. We can compare CRO with fast XY plotters. They display input signal versus another signal (which in most of the cases is time). The luminous spot traces waveform of input voltage with respect to time and therefore we see the wave moving.
CRO operates on voltages and using transducers we are able to convert everything (say strain, current and displacement) into voltages. So we can get visual representation of several phenomena. CRO have improved and evolved continuously. Now there are a number of inbuilt features present in CRO. Some of the CROs can measure frequencies up to 1GHz and some to 20 Hz. They have inbuilt counters and multimeters. Few are even microprocessor controlled. Earlier monochromatic oscilloscopes were used but now a days color oscilloscopes are replacing them in computer and television.
CRO itself consists of many parts. The most important among them are as follows:
Cathode Ray Tube
CRT is the most important part of CRO. The main parts of CRT include
- Electron gun assembly
- Deflection plate assembly
- Fluorescent screen
- Glass envelope and base
As it is very clear from the name itself electron gun assembly releases a sharp and a much focused beam of electrons. When this beam strikes with fluorescent screen it causes a luminous spot. We provide voltage to the deflection plates and these plates deflect the beam. CRT is enclosed in a glass envelope as it provides perfect environment for movement of electrons. Base is a part through which connections are made to various parts.
How electron beam was created in side CRO…
In simple words we can say it is created by electron gun. It is the source of electron beam. But it also constitutes of many parts. These are Heaters, Cathode, Pre-accelerating Anode, accelerating Anode, Focusing Anode and Grid.
Electrons are emitted from heated cathode, these electrons then pass through small hole in grid. Accelerating and pre accelerating anode provide acceleration to the electrons. And the focus is given by focus anode.
Focusing of electron beam can be done by two methods, one is Electrostatic focusing and other is Electromagnetic focusing. CRO uses electrostatic method.
TYPES OF OSCILLOSCOPES:
In Cathode Ray Oscilloscope CRO, broadly there are three categories:
- Multi input oscilloscope (Dual trace oscilloscope and Dual beam oscilloscope)
- Sampling oscilloscope
- Storage oscilloscope (Analog storage and Digital storage)
ACCESSORIES OF CRO:
We calibrate our instruments to get accurate readings. Similarly, calibrators enable CRO amplifier and time base to be calibrated and they can also be checked for accuracy.
Probes in simple words are connection wires used to connect test circuit to CRO. They are again of three types:
- Direct reading probe
- Circuit isolation probe
- Detector probe
In order to permanently record the traces of oscilloscope for analyzing we use camera. Those are special cameras meant only for this purpose. They are again of two types:
- 35 mm film
- Polaroid film
Generally all the electrical instruments have undergone a drastic change from the size to functionality with advent of technology. But CRO has not changed much, a number of functions have been added to this device but still its size, its control panel is almost same. With added functionality buttons on the control panel have increased but still the CRO resembles its older version.
This Article was originally submitted by Ms. Priya Shukla pursuing B.Tech in Electronics & Instrumentation.