Cathode Ray Oscilloscope | CRO

A cathode ray oscilloscope (CRO), also known as an oscilloscope or scope, is a scientific instrument used to graphically display and analyze electronic signals. It uses a beam of electrons, called cathode rays, that are accelerated and directed onto a phosphorescent screen to produce a visible trace. The cathode ray tube (CRT) at the heart of a CRO consists of an electron gun, which produces a beam of electrons, and a pair of deflection plates that deflect the electron beam in the x and y directions, allowing it to be directed to any point on the screen. When the beam strikes the phosphorescent screen, it creates a visible dot that moves across the screen in response to changes in the electronic signal being measured. CROs are commonly used in a variety of applications, such as in the field of electronics for circuit testing and analysis, in medicine for monitoring physiological signals, and in physics for studying waveforms and oscillations. They are essential tools for engineers, scientists, and technicians who need to measure and analyze electronic signals in real-time.CRO monitor

Working of Cathode Ray Oscilloscope(CRO):-



  1. Input signal: The electronic signal to be analyzed is applied to the input terminals of the CRO. The signal can be from any source, such as a generator, amplifier, or sensor.
  2. Amplification and conditioning: The signal is amplified and conditioned to bring it to the required level for display. Amplification can be done using a range of circuits, including operational amplifiers, transistors, or vacuum tubes.
  3. Deflection: The amplified signal is then applied to the deflection plates of the CRT. The deflection plates generate a magnetic field that deflects the electron beam produced by the electron gun, causing it to move across the phosphor screen in the x and y directions.
  4. Display: As the electron beam moves across the screen, it generates a trace that represents the input signal. The trace is visible on the phosphor screen and can be viewed in real-time.
  5. Triggering: In order to capture and stabilize the signal, the CRO has a trigger circuit that synchronizes the electron beam to the input signal. The trigger circuit sets a reference point for the signal, allowing the user to capture and analyze the waveform accurately.
  6. Measurement: The CRO can perform various measurements on the displayed waveform, such as amplitude, frequency, and phase. These measurements are displayed on the screen and can be used to analyze and diagnose the input signal.

Construction of CRO:-

A cathode ray oscilloscope (CRO) consists of several main components that work together to display electrical waveforms on a screen. Here are the main components of a CRO and their construction:

  1. Electron Gun: The electron gun is the part of the CRO that generates and directs a beam of electrons towards the screen. It consists of a cathode, control grid, and accelerating anode. The cathode is a heated filament that emits electrons, the control grid is used to control the electron beam, and the accelerating anode accelerates the electrons towards the screen.
  2. Deflection System: The deflection system is responsible for deflecting the electron beam horizontally and vertically to generate the waveform on the screen. It consists of two sets of deflection plates, one for horizontal and one for vertical deflection. The deflection plates are connected to a set of amplifiers that generate the voltage required to deflect the beam.
  3. Screen: The screen is the part of the CRO that displays the waveform generated by the electron beam. The screen is coated with a phosphorescent material that emits light when struck by the electron beam.
  4. Power Supply: The power supply provides the various voltages required to operate the CRO, including the high voltage required for accelerating the electron beam and the low voltage required for heating the cathode filament.
  5. Trigger Circuit: The trigger circuit is used to stabilize the waveform on the screen by triggering the beam to start at a specific point in the signal. The trigger circuit consists of a trigger level control and a trigger source selector.
  6. Control Circuit: The control circuit is used to adjust the various parameters of the CRO, including the sensitivity, timebase, and triggering level. It consists of various knobs and buttons that allow the user to adjust the settings of the CRO.
  7. Housing: The housing of the CRO is typically made of metal and provides a sturdy and stable platform for the various components. It also includes a handle and other features for easy transport and storage.

Types of CRO:-

There are several types of cathode ray oscilloscopes (CROs), each designed for specific applications. Here are some of the most common types:

  1. Analog CROs: These are traditional CROs that use analog circuits to process and display electronic signals. They have a relatively low bandwidth and a limited set of features but are still widely used in many applications.
  2. Digital CROs: These use digital signal processing (DSP) techniques to analyze and display electronic signals. They have a higher bandwidth and more advanced features, such as waveform capture and automatic measurements.
  3. Mixed Signal CROs: These combine both analog and digital signal processing capabilities in a single instrument. They can display both analog and digital signals simultaneously and are used in applications that require the measurement of both types of signals.
  4. Storage CROs: These have the ability to capture and store a waveform for later analysis. They are used in applications where it is necessary to capture and analyze a waveform that occurs too quickly to be seen in real-time.
  5. Sampling CROs: These are specialized CROs that use a sampling technique to capture high-frequency signals. They have a very high bandwidth and are used in applications such as telecommunications and high-speed digital design.
  6. Portable CROs: These are compact and lightweight CROs that are designed for field use. They are battery-powered and have a small form factor, making them ideal for on-site testing and troubleshooting.

Specification of CRO:-

The specifications of a cathode ray oscilloscope (CRO) are the various parameters that define its performance capabilities. Here are some of the common specifications of a CRO:

  1. Bandwidth: The bandwidth of a CRO is the frequency range over which it can accurately display signals. It is specified in Hertz (Hz) and is typically measured as the frequency at which the amplitude of a sinusoidal waveform is reduced to 70.7% of its maximum value. The bandwidth of a CRO is a crucial specification that determines its ability to display high-frequency signals accurately.
  2. Rise Time: The rise time of a CRO is the time taken for the trace to rise from 10% to 90% of its maximum value. It is specified in seconds (s) and is inversely proportional to the bandwidth of the CRO. A faster rise time indicates that the CRO can display fast-changing signals accurately.
  3. Input Impedance: The input impedance of a CRO is the resistance presented by its input circuit to the signal source. It is specified in ohms (Ω) and is important to ensure that the CRO does not load the signal source and affect the accuracy of the measurement. The input impedance of a typical CRO is in the range of a few megaohms.
  4. Sensitivity: The sensitivity of a CRO is the smallest input signal that it can detect and display. It is specified in volts (V) per division and is important for accurately displaying low-level signals. The sensitivity of a typical CRO is in the range of a few millivolts per division.
  5. Accuracy: The accuracy of a CRO refers to the degree of closeness of its displayed measurements to the actual values of the input signal. It is affected by various factors such as the quality of the internal components, calibration accuracy, and temperature stability. The accuracy of a CRO is usually specified as a percentage of the full-scale value.
  6. Input Coupling: The input coupling of a CRO refers to the method used to connect the input signal to the CRO’s input circuit. There are two types of input coupling: AC coupling and DC coupling. AC coupling blocks the DC component of the signal, while DC coupling allows the DC component to pass through. The input coupling is important to ensure that the CRO displays the correct waveform.
  7. Triggering: The triggering of a CRO is the method used to stabilize the waveform on the screen. It is important to ensure that the waveform is displayed accurately and is not affected by noise or other disturbances. The triggering of a CRO can be set to various levels and modes depending on the signal being measured.

Application of CRO:-

Cathode ray oscilloscopes (CROs) have a wide range of applications in various fields, including:

  1. Electronics: CROs are used to analyze and diagnose electronic circuits, such as amplifiers, filters, and oscillators. They can measure voltage, current, frequency, phase, and other parameters of an electronic signal. They are also used to troubleshoot faults and defects in electronic equipment.
  2. Telecommunications: CROs are used to analyze and measure the characteristics of signals transmitted over communication channels. They can measure signal strength, distortion, noise, and other parameters. They are used in the design and testing of communication systems such as fiber optic, wireless, and satellite systems.
  3. Medicine: CROs are used in medical equipment to measure and analyze physiological signals such as ECG, EEG, and EMG. They are used to diagnose heart conditions, brain disorders, and muscular diseases.
  4. Automotive: CROs are used in automotive diagnostic equipment to measure and analyze signals from various sensors and actuators in the engine, transmission, and other systems. They are used to diagnose faults in the electrical and electronic systems of vehicles.
  5. Aerospace: CROs are used in the design and testing of aerospace systems such as satellites, rockets, and aircraft. They are used to measure and analyze signals from various sensors and instruments in the systems.
  6. Research: CROs are used in scientific research to study waveforms and oscillations in various fields such as physics, chemistry, and biology. They are used to measure and analyze signals from various types of equipment and instruments used in research.

Read Also