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Measurement Equipments
An oscilloscope is an electronic device used to display and analyze time-varying electrical signals. It is a fundamental tool in electronics, electrical engineering and other related disciplines. Oscilloscopes graphically show how an electrical signal changes as a function of time, allowing engineers and technicians to observe and measure various aspects of the signal, such as amplitude, frequency, waveform, period, peak-to-peak voltage, and much more. .
A typical oscilloscope consists of an LCD or cathode ray tube display on older instruments, on which the signal waveform is displayed. The user can adjust the time scale and voltage scale to focus on specific details of the signal being measured. Additionally, oscilloscopes can have multiple channels to measure and display multiple signals simultaneously.
Oscilloscopes are used in a wide variety of applications, from troubleshooting electronic circuits to signal analysis in communications, process control, scientific research, and electronic product development. Their ability to visualize and measure the characteristics of a signal makes them an essential tool for those working with electronics and electricity.
There are several types of oscilloscopes, and their choice depends on the specific needs of the application and the environment in which they will be used. Some of the most common types of oscilloscopes include:
These oscilloscopes use a cathode ray tube (CRT) to display the signal on a screen. Although they have been largely replaced by digital oscilloscopes, they are still used in some applications or for teaching.
An analog oscilloscope worked using analog electronic technology to measure and display electrical signals over time. Next, I will explain how it worked in general:
Signal input: The oscilloscope had one or more signal inputs, to which the measurement probes were connected. These probes were connected to the points of the circuit that were to be measured and sent the signal to the oscilloscope.
Amplification: The input signal was electronically amplified to adjust it to an amplitude suitable for display on the oscilloscope screen. This was achieved through user-controlled amplification stages, allowing the voltage scale to be adjusted.
Vertical Deflection: The amplified signal was applied to the vertical deflection plates of a cathode ray tube (CRT) inside the oscilloscope. The CRT was coated with an electron-sensitive phosphor coating.
Horizontal deflection: The oscilloscope generated a horizontal scan signal that controlled the speed at which the electron beam moved horizontally on the CRT screen. This sweep signal was synchronized with the input signal to ensure that the waveform was displayed correctly on the screen.
Display: As the electron beam moved horizontally and was deflected vertically by the input signal, it generated a line on the CRT screen that formed the graphical representation of the signal. The luminescence of the phosphor on the screen responded to the amplitude of the signal, allowing the waveform to be seen on the screen.
Time Control (Time Base): The user could adjust the horizontal scan speed to control the time scale on the screen, allowing specific details of the waveform to be observed.
Additional Features: Analog oscilloscopes often had additional controls and features, such as the ability to add multiple traces on the same screen, trigger controls to synchronize the display with specific events, and calibration functions.
In short, an analog oscilloscope used a cathode ray tube (CRT) and analog electronic technology to display and measure electrical signals as a function of time. Although analog oscilloscopes have been largely replaced by digital oscilloscopes in most modern applications, they are still used in certain specific applications due to their ability to handle high frequency signals and smoothness in waveform representation.
A digital oscilloscope (DSO) works differently than an analog oscilloscope and uses digital technology to measure and display electrical signals as a function of time. Here is how a digital oscilloscope works in general:
Signal capture: The input signal is acquired using measurement probes connected to the oscilloscope inputs. These probes convert the analog electrical signal into a digital signal that is processed in the oscilloscope.
Digitization: The analog signal is converted into digital data through a digitization process. An analog-to-digital converter (ADC) samples the signal at regular intervals and assigns a digital value to each sample. The sampling rate and resolution of the ADC are important factors in measurement accuracy.
Storage Memory: The resulting digital data is stored in the oscilloscope's internal memory for further processing and display. The amount of memory available in the oscilloscope affects the data storage capacity and the length of waveform that can be captured.
Digital Processing: Once the signal has been digitized and stored in memory, the oscilloscope applies various digital processes, such as scaling, probe attenuation compensation, and calibration, to ensure accurate measurements.
On-screen display: The processed signal is displayed on the oscilloscope screen in a graphical representation, usually in a waveform versus time. The display can be a cathode ray tube (CRT) display or an LCD display on more modern oscilloscopes.
Additional Features: Digital oscilloscopes typically offer a wide range of additional features, such as automatic measurements, cursors, advanced triggering capabilities, data storage and analysis, as well as the ability to connect to computers for data processing and reporting. .
In short, a digital oscilloscope uses digital technology to capture, process, and display electrical signals as a function of time. Signal digitization allows for greater measurement versatility and accuracy, as well as the ability to perform more advanced analysis compared to analog oscilloscopes.
The advancement of technology and the needs of designers and industry have meant that digital oscilloscopes have also increased in performance, so that we have some more specialized variants:
MSO oscilloscopes are a variant of digital oscilloscopes: they combine the capabilities of a digital oscilloscope with the ability to measure multiple channels like an analog oscilloscope. They are useful for applications involving multiple simultaneous signals, such as data buses in digital systems.
These oscilloscopes have significantly greater storage capacity than standard oscilloscopes, allowing them to capture and analyze long sequences of data continuously, even at high sampling rates.
These oscilloscopes combine the functionality of an oscilloscope with that of a logic analyzer, allowing both analog and digital signals to be analyzed in a single instrument.
The primary differences between a sampling and storage oscilloscope (MSO) and a digital oscilloscope (DSO) lie in their ability to measure and display digital signals, especially as it relates to the capture and analysis of multiple digital channels. Here's a more detailed comparison:
Signal capture:
DSO (Digital Oscilloscope): A DSO is primarily used to measure and display analog signals. It can have multiple analog channels, allowing multiple analog signals to be displayed at the same time. Some models may have options to decode and display digital signals, but their primary functionality focuses on analog signals.
MSO (Sampling and Storage Oscilloscope): An MSO is designed for the measurement and display of both analog and digital signals. It combines the functionality of a digital oscilloscope (DSO) with the ability to measure digital signals, such as data buses. It can have analog channels and digital channels, allowing simultaneous display of signals of both types.
Digital channels:
DSO: A DSO generally does not have integrated digital channels. If you need to measure digital signals with a DSO, you generally need to use external logic probes and connect them to the digital pins of the device you want to analyze.
MSO: An MSO has built-in digital channels, meaning you can measure digital signals directly without the need for additional logic probes. This makes it especially useful for debugging and analyzing digital systems.
Visualization and analysis of digital signals:
DSO: While some DSOs have the ability to display digital signals through external logic probes, their functionality for analyzing digital signals may be limited compared to an MSO. Most of the time, a DSO is used to analyze analog signals.
MSO: An MSO is designed to capture, display and analyze both analog and digital signals. You can see the relationship between analog and digital signals in a single instrument, making it easy to troubleshoot systems that combine both types of signals.
In summary, the main difference between a sampling and storage oscilloscope (MSO) and a digital oscilloscope (DSO) is the MSO's ability to measure and display digital signals, along with analog signals, making it more suitable for applications involving complex digital systems. While a DSO focuses primarily on analog signals, an MSO provides more complete functionality for those working with mixed signals.
Sampling rate and bandwidth are two important specifications in an oscilloscope that determine its ability to measure and represent electrical signals. These two parameters are related and are essential to understanding an oscilloscope's ability to accurately capture and display signals.
Sample rate is the number of data points per second that an oscilloscope can capture and record from a signal. It is measured in samples per second or in hertz (Hz).
In a digital oscilloscope (DSO), the sampling rate determines how well it can reproduce the waveform of a signal. To accurately represent a signal, the oscilloscope must sample at a frequency at least twice as high as the maximum frequency present in the signal, according to the Nyquist-Shannon theorem. This is known as the Nyquist criterion.
For example, if you wanted to capture and represent a 100 MHz signal accurately, you would need an oscilloscope with a sample rate of at least 200 MS/s (millions of samples per second).
Choosing the appropriate sample rate is critical to avoid undersampling and signal distortion in the oscilloscope.
The bandwidth of an oscilloscope refers to the range of signal frequencies that the oscilloscope can accurately measure and display. It is measured in hertz (Hz).
Bandwidth determines the ability of an oscilloscope to reproduce high-frequency signals without attenuating or distorting them. An ideal oscilloscope should be able to display sinusoidal signals up to its maximum bandwidth with less than 3 dB (decibel) attenuation.
For example, an oscilloscope with a bandwidth of 100 MHz can effectively represent sinusoidal signals up to 100 MHz without distorting them significantly.
It is important to select an oscilloscope with adequate bandwidth for specific applications, as insufficient bandwidth will limit the ability to measure high frequency signals accurately.
In summary, sampling rate and bandwidth are two key parameters in choosing a digital oscilloscope. The sampling rate determines the amount of data captured per second, while the bandwidth defines the range of frequencies that the oscilloscope can effectively measure. Both parameters should be carefully considered when selecting an oscilloscope for specific applications.
It is true that in digital oscilloscopes, unlike analog oscilloscopes, we could be taking a signal sample and not see a certain peak or rapid change that occurs between sample and sample at a given moment, such as due to interference, but Fortunately, nowadays the sampling frequencies of digital oscilloscopes are usually much higher than the requirements of the Nyquist criterion.
Cursors on an oscilloscope are tools that allow users to accurately measure and perform quantitative analysis of the waveforms displayed on the oscilloscope screen. Cursors are used to determine specific values of the signal, such as amplitude, period, frequency, rise time, fall time and other important parameters. There are two main types of cursors on an oscilloscope:
Vertical Cursor: Vertical cursors are used to measure the signal amplitude on the oscilloscope screen. The amplitude of an electrical signal is the maximum magnitude of its instantaneous value relative to a reference point, usually the value zero. It is measured in units of volts (V) and determines the height of the signal relative to the horizontal axis. Users can place two vertical cursors at specific points on the waveform and the oscilloscope will automatically display the amplitude difference between the two selected points.
Horizontal Cursor: Horizontal cursors are used to measure time on the oscilloscope screen. You can place two horizontal cursors at specific points on the waveform and the oscilloscope will automatically display the time difference between the two selected points.
Some common functions that can be performed with oscilloscope cursors include:
Peak-to-peak voltage (Vpp) is a measure of the voltage difference between the highest positive value and the lowest negative value of a periodic electrical signal or waveform on an oscilloscope. In other words, peak-to-peak voltage represents the total amplitude of a signal from its highest point to its lowest point in a single cycle.
To calculate the peak-to-peak voltage of a signal, you simply subtract the minimum value (usually the most negative value) from the maximum value (usually the most positive value) of the signal. The basic formula is:
Vpp = Vmax - Vmin
Where:
Vpp is the peak-to-peak voltage.
Vmax is the maximum value of the signal.
Vmin is the minimum value of the signal.
For example, if you have a waveform that ranges between +5 volts and -3 volts, the peak-to-peak voltage would be:
Vpp = 5 V - (-3 V) = 8 volts
Therefore, in this case, the peak-to-peak voltage is 8 volts.
Peak-to-peak voltage is an important measurement in electronics and signal analysis as it provides information about the total amplitude of a signal and can be useful in determining whether a signal is suitable for a specific application or in making precise measurements of the signal.
The RMS (Root Mean Square) value of a signal is a measure of the effective magnitude of a signal that varies over time. It represents the direct equivalent value of an alternating signal, that is, the value that an alternating current signal would have if it were converted into a direct current signal with the same dissipated power.
The RMS value is calculated by the square root of the mean of the squares of the instantaneous values of the signal in a given period of time.
However, in the context of electrical signals we must not forget what we call the form factor of an electrical signal.
"Form factor" in the context of electrical signals refers to the relationship between the peak value of a signal and its RMS (Root Mean Square) value. Form factor is a measurement that provides information about how a signal oscillates around its RMS value. It is commonly used in electronics and signal analysis to characterize the waveform of a signal and understand how its amplitude varies with respect to its RMS value.
The form factor is calculated by dividing the peak value of the signal by its RMS value, and is generally expressed as a ratio or in decibels (dB):
Form Factor = Peak Value / RMS Value
Form Factor (in dB) = 20 * log10(Peak Value / RMS Value)
A form factor of 1 indicates that the signal has a sinusoidal waveform, since the peak value is equal to the RMS value in a pure sinusoidal signal. If the form factor is greater than 1, it means that the signal has higher peaks compared to its RMS value and is therefore more "peaky" or "pulseful" in its waveform. If the form factor is less than 1, the signal has lower peaks compared to its RMS value and is more "flattened" or "smoothed" in its waveform.
Therefore the RMS value is an important measurement in electronics and signal analysis because it is related to the actual power dissipated by a signal in an electrical component, such as a resistor. When working with alternating current signals, such as mains signals or audio signals, the RMS value is commonly used to express the effective amplitude of the signal and calculate the actual power consumed or delivered by the signal.
The frequency of a periodic signal is a measure that indicates the number of complete cycles (or repetitions) that occur in the signal in a specific period of time. In other words, frequency represents how quickly a signal repeats or changes over time and is measured in hertz (Hz).
The hertz (Hz) is the unit of measurement for frequency and is defined as one cycle per second. For example, if a signal has a frequency of 100 Hz, it means that it repeats or changes 100 times in one second.
In summary, frequency is a fundamental characteristic for describing and working with signals in a variety of applications in electronics, communications, music, and many other areas.
The period is the inverse of the frequency and represents the duration of one complete cycle of the signal. It is expressed in seconds (s) and is equal to 1 divided by the frequency (T = 1/f)
Rise time and fall time are two parameters used to describe the speed at which a signal changes from one voltage level to another in a waveform. These times are particularly important in the characterization of digital and analog signals, and their measurement is essential in electronics, communications and signal analysis applications. Here's what rise time and fall time are:
Rise time, also known as rise time or rise time, is the time it takes for a signal to change from 10% to 90% of its maximum value or from 20% to 80% of its value. maximum. It is measured from the point at which the signal begins to rise to the point at which it reaches the required level.
Rise time is important in digital applications because it affects the ability of electronic circuits to change state quickly and accurately. A shorter rise time allows for faster transition between states and is therefore desirable in high-speed digital systems.
In summary, rise time and fall time are two parameters that describe the speed at which a signal changes level in a waveform. They are essential for evaluating the speed and accuracy of signal transitions in electronics and communications applications. Rise time refers to the change from a low level to a high level, while fall time refers to the change from a high level to a low level.
Pulse width, often called "pulse width" or "duty cycle", is a parameter used to describe a periodic signal, especially in the context of square waveform or pulse signals. Pulse width represents the proportion of time that a signal is in its active (high) state relative to the signal's entire period.
Pulse width is typically expressed as a percentage or fraction of the signal period. For example, if you have a square signal with a 50% duty cycle, it means that the signal is in its active state (high) for half the period and in its inactive state (low) for the other half of the period. This is represented as a 50% duty cycle.
The pulse width calculation is done as follows:
Pulse Width = (Duration in active state / Period) * 100%
Where:
Active Duration: The time during which the signal is in its active (high) state.
Period: The complete time of one signal cycle.
Pulse width is an important characteristic in control and modulation signals, as it determines how long a signal is active compared to its total period. For example, in a pulse width modulation (PWM) signal, the pulse width controls the amount of power delivered to a device or component during one cycle. Pulse width is also used in describing the frequency and switching speed of digital signals, as well as in power electronics and control applications.
In summary, the cursors on an oscilloscope are especially useful when you need to make precise measurements on a waveform or when you are evaluating specific characteristics of a signal. They allow users to quantify and analyze data more accurately, which is essential in laboratory applications, electronic design, troubleshooting, and circuit testing.
To measure electrical signals with an oscilloscope, you can follow the following general steps:
Turn on the oscilloscope and let it warm up for a few minutes if necessary. Connect the appropriate measurement probes to the oscilloscope. Make sure the probes are in good condition and calibrated if necessary.
Connect the measurement probe to the source of the signal you want to measure.
Set the probe coupling switch according to the signal type: AC (alternating) for alternating current signals and DC (direct current) for direct current signals.
Adjust the voltage scale of the probe so that it is appropriate for the signal you are measuring. This is done using the vertical scale adjustment button.
Adjust the time scale on the horizontal axis so that you can properly see the signal on the screen. This is done using the horizontal scale adjustment button.
Set the sweep speed (sampling rate) of the oscilloscope according to the signal you want to measure.
Configures the oscilloscope's trigger function to stabilize the signal display. Triggering allows the oscilloscope to synchronize the signal display with specific events, such as rising or falling edges.
Adjusts the trigger level so that the oscilloscope correctly synchronizes with the signal. This is done using the trigger level adjustment button.
Observe the signal waveform on the oscilloscope screen. You can use cursors to measure specific values, such as amplitude, rise time, fall time, period, frequency, and more.
Use the oscilloscope's automatic measurement features if available to obtain accurate signal measurements.
If necessary, use the storage function to capture and analyze the signal in more detail. Some oscilloscopes allow you to save and review waveforms for later analysis.
Once you have completed your measurements, turn off the oscilloscope appropriately and disconnect the measurement probes.
Remember that settings and procedures may vary depending on the model and brand of oscilloscope, so consult the user manual for the specific oscilloscope you are using for detailed and accurate instructions.
