회사 소식 Oscilloscope Evolution From CRO to DSO in Modern Electronics

In the vast world of electronic engineering, the oscilloscope serves as an experienced detective, helping engineers uncover circuit mysteries and capture subtle signal variations. From laboratories to production lines, from scientific research to fault diagnosis, oscilloscopes are ubiquitous. But do you truly understand how this "detective" works and how to select the right model for different needs? This article provides an in-depth look at oscilloscopes, from classic Cathode Ray Oscilloscopes (CRO) to modern Digital Storage Oscilloscopes (DSO), offering comprehensive insights into this essential electronic measurement tool.

The Cathode Ray Oscilloscope (CRO) is a classic electronic testing instrument centered around the cathode ray tube (CRT). By displaying voltage waveforms over time on a fluorescent screen, CROs help engineers analyze various signal characteristics such as amplitude, frequency, rise time, and distortion. Its operation relies on electron beam deflection in electric fields, using the beam's movement to depict input signal patterns.

A standard CRO consists of several key components:

• Cathode Ray Tube (CRT): The heart of the CRO, it generates an electron beam, accelerates and focuses it onto the fluorescent screen. When the beam strikes the screen, it produces visible light spots.
• Power Circuit: Requires both high and low voltage supplies. Low voltage heats the electron gun to generate the beam, while high voltage accelerates it. Additional voltages power other control units.
• Deflection Plates: Horizontal (X-axis) and vertical (Y-axis) plates positioned between the electron gun and screen deflect the beam based on input signals. The horizontal deflection typically comes from a time-base generator, creating a linearly changing voltage for uniform scanning.
• Vertical Amplifier: Amplifies input signals before applying them to vertical deflection plates, controlling beam movement vertically.
• Trigger Circuit: Synchronizes horizontal and vertical deflections to stabilize waveform display. Triggering can be based on input signals, external signals, or power line frequency.

CRO operation relies on electrostatic control of electron beams. As beams pass through deflection plates, electrostatic forces cause corresponding deflections. By manipulating deflection voltages, beams trace input signal waveforms on the fluorescent screen.

• CRT: Converts electrical signals to visual images.
• Electron Gun Assembly: Generates and controls electron beams, including heater, cathode, grid, and anode components.
• Deflection Plates: Control beam movement vertically and horizontally.
• Fluorescent Screen: Electron beam impacts produce visible light.
• Glass Enclosure: Maintains vacuum conditions and protects internal components.

This critical component emits and focuses electrons into a fine beam:

• Cathode: Coated with strontium and barium oxides for efficient electron emission at moderate temperatures.
• Control Grid: Typically a nickel cylinder positioned before the cathode that regulates beam intensity by controlling electron flow, adjusting screen brightness.
• Anodes: Include pre-accelerating, accelerating, and focusing anodes applying high voltages (≈1500V for acceleration, ≈500V for focusing) to shape the beam.

Beam focusing is achieved through electrostatic or electromagnetic methods, with CROs typically using electrostatic focusing.

After leaving the electron gun, beams pass through vertical (Y-axis) and horizontal (X-axis) deflection plates that independently control up-down and left-right movements, enabling precise screen positioning.

The CRT's front panel features phosphor-coated surfaces where electron impacts convert kinetic energy into visible light through fluorescence.

This vacuum-sealed conical structure has graphite-coated interiors (aquadag) that function as high-voltage electrodes connected to accelerating anodes, assisting beam focus.

Basic CRO circuits include vertical/horizontal deflection systems, synchronization circuits, intensity modulation circuits, and positioning/brightness controls.

Amplifies input signals through attenuators and multi-stage amplifiers to produce clear waveforms on vertical deflection plates.

Similar to vertical systems but typically driven by scan voltages generating time-base signals for horizontal beam movement, displaying temporal signal changes. Scanning modes include:

• Recurrent Scanning: New scans begin immediately after previous ones conclude.
• Triggered Scanning: Idle circuits activate via external triggers.
• Driven Scanning: Free-running scans triggered by measured signals.
• Non-Sawtooth Scanning: Compares voltage differences or frequencies.

Ensure scan-signal synchronization for stable displays using internal signals, external triggers, or power line frequencies.

Adjusts beam intensity by inserting signals between cathode and ground, altering screen brightness.

Regulates waveform position via DC voltages applied to deflection plates.

Modifies control grid potential relative to cathodes to adjust beam intensity and screen brightness.

CROs serve diverse functions in electronics:

• Measuring voltage, current, frequency, inductance, susceptance, resistance, and power factors.
• Analyzing AM/FM circuit characteristics.
• Monitoring signal properties and controlling analog signals.
• Observing resonant circuit waveforms and bandwidth.
• Visualizing voltage/current patterns for decision-making.
• Laboratory research and circuit design verification.
• Phase/frequency comparisons.
• Television, radar, and engine pressure analysis.
• Monitoring neural responses and heartbeats.
• Measuring BH curves in hysteresis loops.
• Plotting transistor characteristics.

• Voltage measurement capability
• Current measurement precision
• Waveform inspection functionality
• Phase/frequency measurement accuracy

• High cost
• Complex maintenance
• Requires complete isolation
• Bulky, heavy, and power-intensive
• Numerous control terminals with steep learning curves

Technological advancements have made Digital Storage Oscilloscopes (DSO) the preferred choice over traditional CROs. DSOs offer superior precision, enhanced functionality, and user-friendly operation. Using analog-to-digital converters (ADCs), DSOs digitize signals for memory storage, enabling complex waveform capture, display, and analysis.

CROs are analog instruments using CRTs, while DSOs are digital devices with LCD/LED displays that convert, store, and analyze signals digitally.

Consider these factors when choosing an oscilloscope:

• Bandwidth: Determines maximum measurable frequency (typically ≥5× signal frequency).
• Sampling Rate: Affects signal detail capture (higher rates improve accuracy).
• Memory Depth: Governs waveform storage capacity (greater depth captures longer signals).
• Triggering: Synchronizes scans with signals (advanced triggers handle complex waveforms).
• Channels: Number of simultaneous measurable signals (multiple channels show signal relationships).
• Application: Specific needs vary (high-frequency circuits require greater bandwidth than low-frequency applications).

From classic CROs to modern DSOs, oscilloscopes remain indispensable tools for electronic engineers. Understanding their operation and proper use enables effective circuit analysis and troubleshooting. When selecting an oscilloscope, carefully evaluate technical requirements to identify the optimal model for your needs.