Since its invention in 1897, the cathode ray oscilloscope (CRO) has come a long way in being used as a means to detect the presence of electrons.
It is an integral part of modern-day oscilloscopes that are used for measuring various waveforms of electrical circuits. An X-Y plotter plots an input signal against another signal or against time, enabling the study of waveforms, transients, time-based or frequency-based analysis.
A CRO is a complex device consisting of many parts and components. Therefore, before going in depth into it, let’s first understand the Cathode Ray Tube (CRT).
Cathode Ray Tube
A CRT is a vacuum tube that acts as the main part through which the functionalities of a CRO is carried out.
It consists of several parts:
- Heater – This part is responsible for heating the cathode.
- Cathode – On being sufficiently heated, electrons are emitted from the cathode. In order to achieve this, a layer of barium oxide is coated on one end of the cathode.
- Grid – It is kept at a negative potential and helps control the intensity of the electron beam moving towards the anode. The entire structure is made from nickel.
- Pre-accelerating anode – Provides acceleration to the anode before entering the Focusing Anode.
- Focusing Anode – It helps align the incoming electron beam.
- Accelerating anode – Its job is to again accelerate the newly aligned electron beam. Note here that both pre-accelerating and accelerating anodes are connected to a common positive potential of 1500 volts.
All these components collectively form the electron gun.
The beam then moves towards a set of horizontal and vertical deflection plates. These provide an electric field that acts on the electron beam, rendering them a vertical and horizontal motion.
After passing through this final stage, the electron beam strikes the fluorescent screen to give a glow.
CRTs generally find applications in forming television screens.
Cathode Ray Oscilloscope (CRO)
Now that we have learnt the basics of how a CRT works, let’s move onto learning about a CRO.
As mentioned, a CRO is a device that is used for measuring and displaying different forms of electrical signals.
It consists of:
- Cathode Ray Tube – Through this mechanism, electrons are emitted and controlled to form the desired signal image on the fluorescent screen.
- Vertical Amplifier – It amplifies the input signal for display on the CRT screen.
- Delay Line – It provides a certain signal delay that is applied to vertical deflection plates of CRT.
- Trigger Circuit − It produces a triggering signal for synchronizing both horizontal and vertical deflections of the electron beam.
- Time base Generator − It produces a sawtooth signal for horizontal deflection of the electron beam.
- Horizontal Amplifier − It amplifies the sawtooth signal and then connects it to the horizontal deflection plates of CRT.
- Power supply − It produces both high and low voltages. The negative high voltage and positive low voltage are applied to CRT and other circuits respectively.
Through this procedure, a CRO displays the applied input signal on the screen of CRT, providing signals in the time domain.
Applications:
- While numerous, a CRO can be used for the following purposes:
- To determine the amplitude of a waveform.
- Comparison between the phases and frequencies of electrical signals.
- Help measure capacitance and inductance values.
- In the medical field and medical trials, it can be used for monitoring various body parameters like heartbeat rates and nervous reactions.
