Introduction to the method of measuring voltage with an oscilloscope
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 converted to a voltage value. Quantitative test voltage, generally the Y-axis sensitivity switch to the fine-tuning knob "calibration" position, so that the measured voltage value can be calculated directly from the "V / div" indication value and the measured signal occupied by the vertical axis coordinate value. Therefore, the direct measurement method is also known as the scale method.
(1) DC voltage measurement
The Y-axis input coupling switch is placed in the "ground" position, the trigger switch is set to "automatic" position, so that the screen displays a horizontal scanning line, this scanning line will be the zero level line.
Y-axis input coupling switch set to "DC" position, adding the measured voltage, at this time, the scanning line in the direction of the Y-axis to produce a jump displacement H, the measured voltage that is "V / div" switch indicator value and the product of H.
Direct measurement method is simple and easy, but the error is large. Error factors are reading errors, parallax and oscilloscope system errors (attenuator, deflection system, oscilloscope edge effect) and so on.
(2) AC voltage measurement
The Y-axis input coupling switch is placed in the "AC" position, showing the AC component of the input waveform. If the frequency of the AC signal is very low, the Y-axis input coupling switch should be placed in the "DC" position.
Move the measured waveform to the centre of the oscilloscope screen, use the "V/div" switch to control the measured waveform in the range of the effective working area of the screen, and read the degree H in the Y-axis direction occupied by the whole waveform according to the index of the coordinate scale piece, then the peak-to-peak value of the measured voltage VP-P can be equal to the value indicated by the "V/div" switch. The peak-to-peak value of the measured voltage VP-P can be equal to the product of "V/div" switch indication value and H. If a probe is used, the attenuation of the probe should be taken into account, i.e. multiply the above calculated value by 10.
For example, the oscilloscope's Y-axis sensitivity switch "V / div" is located in the 0.2 level, the measured waveform accounted for the Y-axis coordinate amplitude H is 5div, then the peak-to-peak value of the signal voltage is 1 V. If it is measured by the probe, still indicates the above value, then the peak-to-peak value of the measured signal voltage is 10V.
2. Comparative measurement method
Comparative measurement is a known standard voltage waveform and the measured voltage waveform to compare the measured voltage value.
The measured voltage Vx into the oscilloscope's Y-axis channel, adjust the Y-axis sensitivity selector switch "V / div" and its fine-tuning knob, so that the fluorescent screen shows a convenient measurement of the height of the Hx and make a good record, and "V / div" switch and fine-tuning knob location Keep the position of "V/div" switch and trimmer knob unchanged.
Remove the measured voltage, input a known adjustable standard voltage Vs into the Y-axis, and adjust the output amplitude of the standard voltage so that it displays the same amplitude as the measured voltage. At this point, the output amplitude of the standard voltage is equal to the amplitude of the measured voltage. Comparison method of voltage measurement can avoid the vertical system caused by and error, thus improving the measurement accuracy.
