Oscilloscope Test Application

Measurement of voltage
Any measurement made using an oscilloscope boils down to a measurement of voltage. The oscilloscope can measure the voltage amplitude of various waveforms, both DC and sinusoidal voltages, as well as the amplitude of pulsed or non sinusoidal voltages. More useful is that it can measure the voltage amplitude of each part of a pulse voltage waveform, such as the impulse or top drop. This is unmatched by any other voltage measuring instrument.
1. Direct measurement method
The so-called direct measurement method is to directly measure the height of the voltage waveform being measured from the screen, and then convert it into a voltage value. When quantitatively testing the voltage, generally turn the tuning knob of the Y-axis sensitivity switch to the "Calibrate" position, so that the measured voltage value can be directly calculated from the indicated value of "V/div" and the vertical axis coordinate value taken by the measured signal. Therefore, the direct measurement method is also called the scale method.
(1) Measurement of AC voltage
Place the Y-axis input coupling switch in the "AC" position to display 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 center of the oscilloscope screen, use the "V/div" switch to control the measured waveform within the range of the effective working area of the screen, and read the degree H of the entire waveform in the Y-axis direction according to the division of the coordinate scale. The peak to peak VP-P of the measured voltage can be equal to the product of the "V/div" switch indication value and H. If a probe is used for measurement, the attenuation of the probe should be calculated, that is, multiply the above calculated value by 10.
For example, if the Y-axis sensitivity switch "V/div" of the oscilloscope is at the 0.2 level, and the coordinate amplitude H of the measured waveform in the Y-axis is 5 div, then the peak to peak value of this signal voltage is 1 V. If the above values are still indicated after the probe measurement, the peak to peak value of the measured signal voltage is 10V.
(2) Measurement of DC voltage
Set the Y-axis input coupling switch to the "ground" position and the trigger mode switch to the "automatic" position, so that the screen displays a horizontal scan line, which is a zero level line.
Set the Y-axis input coupling switch to the "DC" position and apply the measured voltage. At this time, the scan line generates a jump displacement H in the Y-axis direction, and the measured voltage is the product of the "V/div" switch indication value and H.
The direct measurement method is simple and feasible, but the error is relatively large. The factors that cause errors include reading errors, parallax, and systematic errors of oscilloscopes (attenuators, deflection systems, and oscilloscope tube edge effects).
Comparative measurement method
The comparison measurement method is to compare a known standard voltage waveform with the measured voltage waveform to obtain 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 trim knob, so that the fluorescent screen displays a height Hx that is convenient for measurement, and make a record. The positions of the "V/div" switch and trim knob remain 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 to display 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. The comparison method for measuring voltage can avoid errors caused by vertical systems, thereby improving the measurement accuracy.
Measurement of time
The oscilloscope time base can generate scan lines that are linearly related to time, so the horizontal scale of the fluorescent screen can be used to measure the time parameters of the waveform, such as the repetition period of a periodic signal, the width of the pulse signal, the time interval, the rise time (leading edge) and fall time (trailing edge), the time difference between the two signals, and so on.
When the "fine tuning" device of the sweep switch "t/div" of the oscilloscope is turned to the calibration position, the time represented by the displayed waveform on the horizontal scale can be directly read and calculated according to the indicated value of the "t/div" switch, thereby obtaining the time parameters of the measured signal more accurately.