Data expansion:
Oscilloscope is a widely used electronic measuring instrument. It can transform electrical signals invisible to the naked eye into visible images, which is convenient for people to study the changing process of various electrical phenomena. Oscilloscope uses a narrow electron beam composed of high-speed electrons to hit the screen coated with fluorescent substances, which can produce tiny light spots (this is the working principle of traditional analog oscilloscope). Under the action of the measured signal, the electron beam, like a pen tip, can draw the curve of the instantaneous value of the measured signal on the screen. Oscilloscope can be used to observe the waveform curves of different signal amplitudes changing with time, and can also be used to test various electric quantities, such as voltage, current, frequency, phase difference and amplitude modulation.
An instrument for measuring the waveform of alternating current or pulse current consists of an electron tube amplifier, a scanning oscillator, a cathode ray tube, etc. Besides observing the waveform of current, we can also measure the frequency and voltage intensity. Any periodic physical process that can become an electrical effect can be observed with an oscilloscope.
voltage measurement
Any measurement made by an oscilloscope can be attributed to the measurement of voltage. Oscilloscope can measure the voltage amplitude of various waveforms, not only DC voltage and sinusoidal voltage, but also pulse or non-sinusoidal voltage amplitude. More useful, it can measure the voltage amplitude of each part of the pulse voltage waveform, such as overshoot or top drop. This is unmatched by any other voltage measuring instrument.
1. Direct measurement method
The so-called direct measurement method is to measure the height of the measured voltage waveform directly from the screen and then convert it into a voltage value. When quantitatively testing voltage, generally turn the fine-tuning knob of the Y-axis sensitivity switch to the "calibration" position, so that the measured voltage value can be directly calculated from the indicated value of "V/div" and the ordinate value of the measured signal. Therefore, direct measurement method is also called ruler method.
Measurement of (1) AC voltage
Put the Y-axis input coupling switch in the "AC" position to display the AC component of the input waveform. If the frequency of AC signal is very low, the Y-axis input coupling switch should be placed in the "DC" position.
Move the measured waveform to the center of the oscilloscope screen, control the measured waveform in the effective working area of the screen with the "V/div" switch, and read the degree H of the whole waveform in the Y axis direction according to the division of coordinate scale, then the peak-to-peak value VP-P of the measured voltage can be equal to the product of the indicated value of the "V/div" switch and H. If the probe is used for measurement, the attenuation of the probe should be taken into account, that is, the value calculated above should be multiplied by/kloc.
For example, the Y-axis sensitivity switch "V/div" of the oscilloscope is located at step 0.2, and the coordinate amplitude H of the measured waveform on the Y-axis is 5div, then the peak-to-peak value of this signal voltage is1v. If the probe still shows the above values after measurement, the peak-to-peak value of the measured signal voltage is 10V.
(2) Measurement of 2)DC voltage
Set the Y-axis input coupling switch to the "ground" position and the trigger mode switch to the "automatic" position, so that a horizontal scanning line will be displayed on the screen, which is a zero-level line.
Set the Y-axis input coupling switch to the "DC" position, and add the measuring voltage. At this time, the scanning line produces a jump displacement h in the Y-axis direction, and the measured voltage is the product of the indicated value of "V/div" switch and h.
The direct measurement method is simple and easy, but the error is large. The factors causing errors include reading error, parallax and system error of oscilloscope (attenuator, deflection system, oscilloscope tube edge effect) and so on.
2. Compare measurement methods
Comparative measurement method is to compare a known standard voltage waveform with the measured voltage waveform to get the measured voltage value. Input the measured voltage Vx into the Y-axis channel of the oscilloscope, adjust the Y-axis sensitivity selection switch "V/div" and its fine-tuning knob, so that the height Hx convenient for measurement can be displayed on the fluorescent screen and recorded, and the positions of the "V/div" switch and the fine-tuning knob remain unchanged. Remove the measured voltage, input a known adjustable standard voltage Vs on the Y axis, and adjust the output amplitude of the standard voltage to display the same amplitude as the measured voltage. At this time, the output amplitude of the standard voltage is equal to the amplitude of the measured voltage. The comparison method can avoid the sum error caused by vertical system, thus improving the measurement accuracy.
Data reference:
Oscilloscope Baidu encyclopedia