Electronics Fundamentals: Oscilloscope-102 - Detailed Introduction, Types, Safety, Usage, History, Design Concept, MSO/DSO Working Principle

In the previous article on generating a sinusoidal waveform using an Oscilloscope, it was proposed that there are THREE fundamental steps on displaying, plotting, analyzing and stabilizing a waveform, which are the following basic Oscilloscope functions:

1. Horizontal
2. Vertical
3. Trigger

FIG: Lissajous Figures - source: wikipedia

Now, lets ask some of the very basic questions in order to understand "Why Oscilloscope?" and the motivation behind its use in Electronics:

NOTE - The topics and questions marked in color 'Blue' are covered to a certain extent in this post - i.e. 'Oscilloscope-102'. While, the topics covered in 'Red' are more covered in the section 'Oscilloscope-103' and 'Oscilloscope-104'.

1. - Why do we use an Oscilloscope? Why NOT use something simple, like an Ammeter which measures Electric Current? [Using analog oscilloscope as an example.]
2. - What is an Oscilloscope, an explanation? Types of Oscilloscopes?
3. - Brief History, Importance, and Usage of an Oscilloscope?
4. - How is an Oscilloscope designed - Design Concepts? [discussed in detail under 'Oscilloscope-104']
5. - A general architecture / design concept of an Oscilloscope? [discussed in detail under 'Oscilloscope-104']
6. - Basic scope of usage of a usual Mixed Signal Oscilloscope (Digital and Analog). [discussed in more detail in 'Oscilloscope-103']
7. - Why do we analyze/study a Waveform on an Oscilloscope? [discussed in more detail in 'Oscilloscope-103']
8. - What is a Waveform? [discussed in more detail in 'Oscilloscope-103']
9. - What is a Signal? [discussed in more detail in 'Oscilloscope-103']
10. - What is a Frequency? [discussed in more detail in 'Oscilloscope-103']
11. - Various examples and waveforms with their analysis. [discussed in more detail in 'Oscilloscope-103']
12. - Describing general functionality of an Oscilloscope and its features (year 2025). [discussed in more detail in 'Oscilloscope-103']
13. - Real World Utilization of an Oscilloscope (with some examples).[discussed in more detail in 'Oscilloscope-103']

1-A. Why do we use an Oscilloscope?

• Oscilloscope is not the first measuring instrument/device, or a tool to measure an Electrical value (such as current). The intent to measure an Electrical value (such as current or voltage) is not new. During the ancient times, this process of Electric current was observed by watching out for physical phenomenon like heating, bubbling, plating or mechanical movements.

• In modern history, the first observation of an electrical current flow in a wire was observed when a magnetic compass deflected accidently when its kept next to a live wire with electric charge flowing in it. Later on, in modern history, as a need to measure and observe electrical values and signals grew, the concept of a measuring instrument called a Galvanometer/Ammeter and afterwards an Oscilloscope was coined. But why do we use an Oscilloscope and not a simple Ammeter?

The answer to the scope of an Oscilloscope as a measuring instrument lies within the observations of this physicality of Electricity and beyond. The following details and examples is an attempt to clarify on the Oscilloscope usage:

> An Oscilloscope is the most useful and versatile electronic circuit test instrument. It is useful in observing voltages (v) in a circuit as a function of time (t), triggering on a point on the waveform to stationary display results.

FIG: Two-Channel analog oscilloscope (to be explained in more detail later) schematic block diagram (not so much in use nowadays) - source: The Art of Electronics [Horowitz/Hill].

> Scopes are always 'digital' where input signals are digitized, processed, and displayed, but better as their legacy analog legacy instruments.

Features: Below are the main general features defined to demonstrate working of an Oscilloscope. To better understand it, example of an analog scope is used here to explore its features.

FIG: An example scope - front panel - source: The Art of Electronics [Horowitz/Hill].

• Vertical: A two-channel analog scope is useful to find a relationship between signals. Each channel has a calibrated gain switch to adjust how much the signal is amplified or attenuated before it is displayed. It sets how many volts is each vertical division (volts) on the screen. There is also a variable gain knob to set a signal to a certain number of divisions. Better scopes have indicator lights to warn if the variable gain knob is out of the calibrated position. See example knob in previous article.

• Horizontal: Vertical signal is applied to the vertical deflection electronics, moving the dot Up and Down on the screen. The horizontal sweep signal is generated by an internal ramp generator , giving deflection proportional to time. The time divisions knob can, in general, magnify signal by 10 times on time scale. There are other detailed scopes which are not discussed here which have a very low time scale (picoseconds).

• Trigger(ing): Assuming a sinusoidal (or repetitive) waveform, if the horizontal sweep doesn't catch the input signal at the same point in its waveform, the display will look like a hot mess! Hence, the trigger circuit lets the observer select a LEVEL and SLOPE (+ or -) at which to begin the sweep. If the signal on the screen keeps flickering and highly unstable to observe, placing a trigger on top of the waveform will stabilize the signal so it is easier for user to analyze it.

More details on the above three features (main features) and the Probes will be discussed further in this article later with more explanation and examples.

1-B. Why NOT use something simple, like an Ammeter which measures Electric Current?

Ammeter [source - IEEE std. 100-1992] - An instrument for measuring the magnitude of an electric current. OR An instrument for measuring electric current in amperes.

FIG: Ammeter representation/symbol.

=> It is provided with a scale, usually graduated in either amperes (A) [Electric Current S.I. unit of measurement], milliamperes, microamperes, or kiloamperes, the instrument is usually designated as a milliammeter, a microammeter, or a kiloammeter.

An Ammeter can measure current which can be AC, or DC (galvanometer), and AC/DC.

Thus, using an ammeter for measuring ampere electrical current is a very useful device (DMM- Digital Multi-Meter in use nowadays) for such electrical current measurement which is classically independent of time as a 1-dimensional value, and therefore, an Ammeter cannot be used in place of an Oscilloscope.

Thus, showing the importance of a measuring instrument such as an Oscilloscope.

2. What is an Oscilloscope?

FIG: Front Panel Controls - GA1102CAL / GA1000 series.

As described in the previous article, "A Digital Oscilloscope is a multi-functional instrument for displaying, analyzing, and storing electrical signals. It is an indispensable tool for designing, manufacturing, and maintaining electronic equipment".

• While, the previous article distinctly describes a "digital" oscilloscope, and an "Analog Oscilloscope" is briefly described above in the stated question '1', in general an Oscilloscope is a visible marking instrument for an instantaneous value of a rapidly varying electrical quantities as a function of time or another electrical or mechanical quantity (source - IEEE std. 100-1992).

• An Oscilloscope can also be defined as - A time-varying measuring instrument of voltages, essentially plotting a graph of voltage against time (source - Example Oscilloscope Datasheet: ADS1000 Series / GA1102CAL).

3. Brief History, and Usage of an Oscilloscope and an important pre-history:

The Oscilloscope we know today is not how it used to be. The first Oscilloscope ran on a CRT instead of using current day fancy displays.

What is CRT?

Cathode-Ray Tube:

FIG: Karl Braun's Original CRT [1897].

FIG: Triode - 1900s device used for controlling the flow of electrons developed by Lee De Forest, the first electronic device. 

FIG: Primitive Triode - Lieben-reisz tube. 

Read more about early vacuum tubes in the below reference links below:

• Thermionic Valves
• Asian research report on thermionic valves 
• Vacuum Tubes (source ref. MIT)
• Saga of vacuum tubes
• Radio Telegraphy and Telephone - Thermionic Valves
• Oscilloscope - patent
• Know Your Oscilloscope - (ref. world radio history)

On referencing the above mentioned early electronics devices, the first oscilloscope-like device was introduces in 1924 by Vladimir Zworykin, with improved CRT signal tracing, and visualized electrical signals using electron beams which laid the foundation of an Oscilloscope.

Technically speaking, in simple terms, "an oscilloscope is simply a small television set except that the user has control of what is being displayed." (ref. NJIT Lab Exercise)

FIG: One of V. Zworylin's 1923 Television System patent (image ref. wikipedia).

> First commercial Oscilloscope:

The first commercially available o-scope was made available by General Radio by introducing their type GR Type 535 with a CRT unit and power supply available, along with a separate 506-A Bedell linear sweep module.

FIG: Example parts of CRT region inside the 535A oscilloscope - demonstration from the data sheet mention below (page 152).

See GR Type 535 Data Sheet => TYPE 535A Oscilloscope (open page & download data sheet from here)

> This scope was still a primitive-level oscilloscope compared to the current day scope.

> First truly modern oscilloscope with reliable sweep and triggering was launched by Tektronix - till date a major name in this field of electronics and measuring instruments industry, especially when it comes to the oscilloscopes (y. 1939 Howard Vollum; Jack Murdock). Later, they released a commercial oscilloscope under Tektronix which was Model 511 in y. 1947.

FIG: Tektronix 511 - Front Panel

FIG: 511 non-A power supply schematics

FIG: 511 AD - from September 1948

> Oscilloscope Importance:

• Visualize Electrical Signals.
• Finding Circuit Faults.
• Timing & Voltage Measurement: Amplitude, Frequency, Rise/Fall Time, Phase Difference, Duty Cycle.
• Verification of designed systems in the field of power electronics, rf communications, digital circuits, analog electronics, embedded systems.
• Scientific Discovery - in fields such as quantum physics, aerospace, neuroscience, etc.
• Education, Training.

> Oscilloscope Usage:

• Examples:-
• Arduino pin output/input analysis and its working.
• Power supply noise.
• Diagnosis of LED drivers flickering.

Now lets read the MAIN usage of oscilloscopes mentioned below:

Below are the main 8 use-cases that can be very fruitful if utilized fully:

4 - 5.  Design Concepts - Oscilloscope

Below are the basic subsystems that are needed to design an oscilloscope. We will not discuss each system and design an oscilloscope, but rather get an overview of design concepts.

Here is a sample signal flow inside an oscilloscope: 

Probe → Input → Conditioning → ADC → Memory → DSP → Display

Now, lets choose another post to dive deeper into an 'oscilloscope design' but, the above block diagram shall demo on how the scope design works!

Mixed Signal Oscilloscope and its Usage:

DSO (i.e. Digital Storage Oscilloscope) in general can only analyze an analog signal and store it digitally for the observer's analysis, while, MSO i.e. a Mixed-Signal Oscilloscope has ability to analyze both analog signal by default (usually having 2 to 4 analog channels ranging from 100MHz to 200MHz) along with the ability to analyze digital signals as well by using a Logic Analyzer module which could be provided by the manufacturer as a mandatory or an optional module (with 12 to 16 High Definition channels).

> Before further discussing about an MSO and its Usage, let us understand the general safety information of an Oscilloscope (which was touched in previous post as well under 'oscilloscope-101'):

SAFETY FEATURES (IN DETAIL)

> A DSO or an MSO is generally used in an indoor environment which is clean and dry with an ambient temperature range (consider direct sunlight, electric heaters, other heat sources, while evaluating the ambient temperature). Avoid in explosive, dusty, or humid environments.

Ambient Temperatures:

>  Operating: 0 °C to +50 °C

> Non-operation: -30 °C to +70 °C

Humidity (Relative Humidity = RH):

> Operating: 5% ~ 90% RH, 30°C, De-Rate (i.e. limiting the operational performance) to 50% RH at 50°C

> Non-operating: 5% ~ 95% RH

> Thus, scope will operate only up to 90% humidity in the air causing moisture related damage. Less than 5% RH can cause static electricity.

Altitude:

> Operating: ≤ 3000m, 25 °C

> Non-operating: ≤ 15,000m

Overvoltage:

> Before discussing the overvoltage category, let's understand the categories itself using the below table:

Category	Typical Use Case	Expected Transient Voltage	Example Equipment
CAT I	Signal-level circuits	Less than 500 V	Oscilloscope inputs, lab instruments
CAT II	Local power distribution	Up to 2500 V	TVs, desktop PCs, oscilloscopes
CAT III	Building wiring circuits	Up to 4000 V	Distribution panels, industrial motors
CAT IV	Mains power (outdoor lines)	Up to 6000 V	Utility meters, service entrances

> In general, nowadays, scopes use CAT-2, which refers to devices powered by the local AC mains like a wall outlet in homes or labs.

> Instrument is connected to the building's electrical outlets.

> These devices can handle moderate voltage spikes (transients i.e. short or sharp voltage or current spikes which last microseconds or milliseconds).

> In short, usually the scopes are designed to plugged into wall sockets in labs.

Degree of Pollution:

Pollution Degree	Description	Typical Environment	Airborne Particles (PPM)	Approx. AQI Range
Degree I	No pollution or only dry, non-conductive pollution inside sealed enclosures	Inside cleanrooms, sealed devices	~0–50 ppm	0–50 (Good)
Degree II	Non-conductive pollution that may become temporarily conductive due to condensation (humidity)	Offices, labs, classrooms (indoor use)	~50–300 ppm	0–100 (Good–Moderate)
Degree III	Conductive pollution or dry pollution that becomes conductive when exposed to humidity	Factories, workshops, control rooms	~300–1000+ ppm	100–200+ (Unhealthy)
Degree IV	Persistent, conductive pollution — frequent exposure to wet, dusty, or chemically reactive air	Outdoor substations, marine docks	1000+ ppm	200+ (Very Unhealthy)

> These scopes are safe when operated in up to Pollution Degree II, with light dust, moderate humidity, clean indoor air (AQI ≤ 100). These are not suitable for industrial areas which are dirty or humid, with high particulate levels AQI > 150 or PPM > 500.

Other working environments:

> In general, these scopes have an IP rating of IP20 as per IEC 60529, (2 = protected against solid objects > 12.5 mm like thick wires or fingers; 0 = no protection against water).

> Voltage Range (general): 90 - 264 Vrms

> Frequency Range (general): 47 - 63 Hz

There are more safety features which you may find in any DSO or MSO manual/datasheet. Now, lets get back to MSO.

Below is a Block Diagram which will help understand the MSO or DSO working and its component breakdown:

→Analog Signal 

→ Attenuation 

→ Clean & Buffer (AFE) 

→ Digitize (ADC)

→ Analyze (DSP)

→ Store (Memory) 

→ View (Display)

FIG: The oscilloscope display is seen on the screen after processing the input signal and storing it into the memory. The above block diagram shows the components used before signal or waveform is displayed.

Not to confuse with information overload - rest of the Oscilloscope questions and conceptual topics which we asked in the beginning of this article are covered in the Next Posts, including oscilloscope and MSO features, examples, usage.

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