Oscilloscope beginners must understand the common terms analysis

In the instrument measurement circle, the first instrument a beginner must learn is the oscilloscope. In addition to being able to operate it, it is also necessary to understand the common terms of the oscilloscope. Today, Antai Test will share with you the common terms that oscilloscope beginners must know. Friends who are just getting started, please save them quickly.

1. Bandwidth

Refers to the frequency value when the sinusoidal input signal decays to 70.7% of its actual amplitude, that is, the -3dB point (based on a logarithmic scale). This specification indicates the frequency range that an oscilloscope can accurately measure. Bandwidth determines the basic measurement capability of an oscilloscope for signals.

As the frequency of a signal increases, the ability of an oscilloscope to accurately display the signal decreases. Without sufficient bandwidth, the oscilloscope will not be able to resolve high frequency changes. Amplitudes will be distorted, edges will disappear, and details will be lost. All the features, ringing, and humming you get about your signal are meaningless without sufficient bandwidth.

5x Rule 5x Rule (Oscilloscope bandwidth required = highest frequency component of the measured signal x 5) The measurement error of an oscilloscope selected using the 5x rule will not exceed ±2%, which is generally sufficient. However, as the signal frequency increases, this rule of thumb is no longer applicable. The higher the bandwidth, the more accurate the reproduced signal.

2. Rise time

In the digital world, time measurement is critical. When measuring digital signals, such as pulses and step waves, the rise time may be more important. The oscilloscope must have a long enough rise time to accurately capture the details of fast-changing signals.

Oscilloscope rise time Oscilloscope rise time = fastest rise time of the measured signal + 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 selecting the bandwidth. The faster the oscilloscope's rise time, the more accurately it can capture the rapid changes of the signal.

3. Sampling rate

The sampling rate indicates the frequency at which the oscilloscope samples the input signal within a waveform or cycle. It is expressed as samples per second (S/S). The faster the sampling rate of the oscilloscope, 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 slow-changing signals over a longer time range, the minimum sampling rate becomes more important.

The method for 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 aliasing, the Nyquist theorem dictates that the signal must be sampled at a rate no less than twice its highest frequency component.

However, this theorem assumes an infinitely long and continuous signal. Since no oscilloscope can provide an infinite record length and low-frequency interference is by definition discontinuous, it is not enough to use a sampling rate twice that of the highest frequency component. In fact, the accurate reproduction of the signal depends on its sampling rate and the interpolation method used to interpolate the gaps between the signal sampling points.

When using the sine difference method, in order to accurately reproduce the signal, the oscilloscope's sampling rate must be at least 2.5 times the highest frequency component of the signal. When using the linear interpolation method, the oscilloscope's sampling rate should be at least 10 times the highest frequency component of the signal.

4. Waveform capture rate

Refers to the speed at which the oscilloscope acquires waveforms. All oscilloscopes flash. That is, the oscilloscope captures the signal a certain number of times per second, and no measurements are taken between these measurement points. This is the waveform capture rate, expressed as 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 variation. An oscilloscope with a high waveform capture rate will provide more important signal characteristics and greatly increase the probability of the oscilloscope quickly capturing transient anomalies such as jitter, short pulses, low-frequency interference, and transient errors.

5. Record length

The record length is expressed as the number of points that make up a complete waveform record and determines the amount of data that can be captured in each channel. Since an oscilloscope can only store a limited number of waveform samples, the duration of a waveform is inversely proportional to the oscilloscope's sampling rate.

6. Triggering ability

The trigger function of the oscilloscope synchronizes the horizontal scan at the correct signal position point, which determines whether the signal characteristics are clear. The trigger control button can stabilize repetitive waveforms and capture single pulse waveforms.

7. Valid bits

Effective bits is a measure of an oscilloscope's ability to accurately reproduce a sinusoidal signal waveform. This metric compares the actual error of the oscilloscope to a theoretically ideal digitizer. Since the actual error number includes noise and distortion, the frequency and amplitude of the signal must be specified.

8. Frequency response

Bandwidth alone is not enough to ensure that an oscilloscope accurately captures high-frequency signals. Oscilloscopes are set to target a specific type of frequency response: Maximum Flat Envelope Delay (MFED). This type of frequency response provides excellent pulse fidelity with minimal overshoot and ringing.

Since digital oscilloscopes are made up 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 varies greatly.

8. Vertical sensitivity

Vertical sensitivity indicates the degree to which the vertical amplifier amplifies weak signals, and is usually expressed in millivolts per scale. The typical value of the minimum volt number that a multi-purpose oscilloscope can detect is about 1mv per vertical display scale.

9. Scanning speed

The sweep speed is a measure of how fast the trace sweeps across the oscilloscope display, allowing for finer details to be seen. The sweep speed of an oscilloscope is expressed in time (seconds)/division.

11. Gain accuracy

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

12. Horizontal accuracy

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

13. Vertical resolution

The vertical resolution of an analog-to-digital converter, and therefore a digital oscilloscope, refers to how accurately the oscilloscope converts the input voltage into a digital value. Vertical resolution is measured in bits. Computational methods can increase the effective resolution, such as high-resolution capture mode.