The technical parameters and technical terms commonly used in oscilloscopes

An oscilloscope is a graphical display device that depicts the waveform of electrical signals. This simple waveform can explain many characteristics of the signal: the time and voltage value of the signal, the frequency of the oscillating signal, the frequency of occurrence of a specific part of the "change part" signal in the circuit represented by the signal relative to other parts, and the presence of faulty components Distortion of the signal, the DC and AC components of the signal, the noise value of the signal and the change of the noise with time, comparison of multiple waveform signals, etc.

1. Technical parameters and technical terms: bandwidth

Refers to the frequency value when the sinusoidal input signal is attenuated to 70.7% of its actual amplitude, which is the -3dB point (based on a logarithmic scale). This specification indicates the frequency range that the oscilloscope can accurately measure. The bandwidth determines the basic oscilloscope's ability to measure the signal. As the signal frequency increases, the oscilloscope's ability to accurately display the signal will decrease. If there is not enough bandwidth, the oscilloscope will not be able to distinguish high frequency changes. The amplitude will appear distorted, the edges will disappear, and the details will be lost. If there is not enough bandwidth, all the characteristics about the signal, ringing and ringing are meaningless.

▲ 5 times criterion (the required bandwidth of the oscilloscope = the highest frequency component of the signal under test Х5) The measurement error of the oscilloscope selected using the 5 times criterion will not exceed ± 2%, which is generally sufficient. However, as the signal frequency increases, this empirical criterion is no longer applicable. The higher the bandwidth, the more accurate the reproduced signal.

2. Technical parameters and technical terms: rise time

In the digital world, time measurement is crucial. When measuring digital signals, such as pulses and step waves, it may be more necessary to evaluate the rise time performance. The oscilloscope must have a long enough rise time to accurately capture the details of the rapidly changing signal.

â–² Oscilloscope rise time = the fastest rise time of the signal under test + 5 rise time describes the effective frequency range of the oscilloscope. The basis for selecting the oscilloscope rise time is similar to the basis for bandwidth selection. The faster the oscilloscope's rise time, the more accurate the capture of the rapid transition of the signal.

3. Technical parameters and technical terms: sampling rate

Sampling rate means the frequency that the oscilloscope samples the input signal in a waveform or period. Expressed as samples per second (S / S). The faster the oscilloscope's sampling rate, the higher the resolution and clarity of the displayed waveform, and the lower the probability of losing important information and events. If you need to observe slowly varying signals over a longer time frame, the minimum sampling rate becomes more important.

The method of calculating the sampling rate depends on the type of waveform being measured and the signal reconstruction method used by the oscilloscope. In order to accurately reproduce the signal and avoid confusion, Nyquist's theorem stipulates that the sampling rate of the signal must not be less than twice its highest frequency component. However, the premise of this theorem is based on infinitely long and continuous signals. Since no oscilloscope can provide an unlimited time record length, and by definition, low-frequency interference is discontinuous, so it is not enough to use a sampling rate that is twice the highest frequency component. In fact, the accurate reproduction of the signal depends on its sampling rate and the interpolation method adopted by the signal sampling point gap.

â–² When using the sinusoidal difference method, in order to accurately display the signal, the sampling rate of the oscilloscope must be at least 2.5 times the highest frequency component of the signal. When using linear interpolation, the sampling rate of the oscilloscope should be at least 10 times the highest frequency component of the signal.

4. Technical parameters and technical terms: waveform capture rate

It refers to the speed at which the oscilloscope acquires the waveform. All oscilloscopes will flash. In other words, the oscilloscope captures the signal a certain number of times per second, and no measurements will be taken between these measurement points. This is the waveform capture rate, expressed as the number of waveforms per second (wfms / s). The waveform capture rate depends on the type and performance level of the oscilloscope and has a wide range of changes. Oscilloscopes with high waveform capture rates will provide more important signal characteristics and greatly increase the probability that the oscilloscope will quickly capture transient anomalies such as jitter, runt pulses, low frequency interference, and transient errors.

5. Technical parameters and technical terms: record length

The number of points represented as a complete waveform record determines the amount of data that can be captured in each channel. Since the oscilloscope can only store a limited number of waveform samples, the duration of the waveform is inversely proportional to the sampling rate of the oscilloscope.

6. Technical parameters and technical terms: triggering capability

The trigger function of the oscilloscope scans horizontally and synchronously at the correct signal position, which determines whether the signal characteristics are clear. The trigger control button can stabilize the repeated waveform and capture the single pulse waveform.

7. Technical parameters and technical terms: effective bits

It is a measure of the oscilloscope's ability to accurately reproduce sinusoidal signal waveforms. This metric compares the actual error of an oscilloscope to a theoretically ideal digitizer. Since the actual number of errors includes noise and distortion, it is necessary to specify the frequency and amplitude of the signal.

8. Technical parameters and technical terms: frequency response

Using bandwidth alone is not enough to ensure that the oscilloscope accurately captures high-frequency signals. The goal set by the oscilloscope is a specific type of frequency response: maximum flat envelope delay (MFED). This type of frequency response provides excellent pulse fidelity with minimal overshoot and damped oscillation. Since the digital oscilloscope is composed of actual amplifiers, attenuators, analog-to-digital converters (ADCs), connectors, and relays, the MFED response is only an approximation of the target value. The pulse fidelity of products from different manufacturers is very different.

9. Technical parameters and technical terms: vertical sensitivity

Vertical sensitivity indicates the degree of amplification of a weak signal by a vertical amplifier, usually expressed in millivolts per scale. The typical value of the minimum volts that a multi-purpose oscilloscope can detect is about 1mv per vertical display scale.

10. Technical parameters and technical terms: scanning speed

Scanning speed characterizes how fast the trajectory sweeps across the oscilloscope display so that you can discover more subtle details. The scanning speed of the oscilloscope is expressed in time (seconds) / div.

11. Technical parameters and technical terms: gain accuracy

Gain accuracy is a measure of how accurately a vertical system attenuates or amplifies a signal. It is usually expressed as a percentage error.

12. Technical parameters and technical terms: horizontal accuracy

Horizontal or time-base accuracy refers to the accuracy of the timing of the display signal in a horizontal system, usually expressed as a percentage error.

13. Technical parameters and technical terms: vertical resolution:

The vertical resolution of the analog-to-digital converter, that is, the vertical resolution of the digital oscilloscope, refers to the accuracy of the oscilloscope to convert the input voltage to a digital value. The vertical resolution is measured by the number of bits. The calculation method can improve the effective resolution, such as high-resolution capture mode.

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