How to measure current with Tektronix oscilloscope

What are the methods of measuring voltage with an oscilloscope? We can use an oscilloscope to observe the waveform curves of various signal amplitudes changing with time, and at the same time, we can also measure various electrical quantities, such as voltage, current, etc. The display circuit of an oscilloscope (digital oscilloscope) consists of an oscilloscope tube and its control circuit. The oscilloscope tube is a special electron tube, consisting of an electron gun, a fluorescent screen, and a deflection system. It is an important part of the oscilloscope. Any measurement made with an oscilloscope can be regarded as a measurement of voltage. This article, Antai Test, mainly introduces the method of measuring voltage with an oscilloscope.

1. How to measure voltage with oscilloscope

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 the voltage, generally turn the fine-tuning knob of the Y-axis sensitivity switch to the "calibration" position. In this way, the measured value can be directly calculated from the indicated value of "V/div" and the vertical axis coordinate value occupied by the measured signal. Voltage value. Therefore, the direct measurement method is also called the ruler method.

(1) Measurement of DC voltage

Set the Y-axis input coupling switch to the "ground" position and the trigger mode switch to the "auto" 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 add the measured voltage. At this time, the scanning line generates a jump displacement H in the Y-axis direction. The measured voltage is the product of the "V/div" switch indication value and H.

The direct measurement method is simple and easy to implement, but the error is large. Factors causing errors include reading error, parallax, and oscilloscope system errors (attenuator, deflection system, oscilloscope tube edge effect), etc.

(2) Measurement of AC voltage

Set the Y-axis input coupling switch to 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 effective working area of ​​the screen, and read the Y-axis occupied by the entire waveform according to the graduations of the coordinate scale. The degree of direction H, then the peak-to-peak value 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 taken into account, that is, the above calculated value should be multiplied by 10. For example, the Y-axis sensitivity switch "V/div" of the oscilloscope is at the 0.2 level, and the Y-axis coordinate amplitude H of the measured waveform is 5div, then the peak-to-peak value of this signal voltage is 1V. If measured by the probe, the above value is still indicated, then the peak-to-peak value of the measured signal voltage is 10V.

comparative measurement

The comparative 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 fine-tuning knob, so that the fluorescent screen displays the height Hx that is convenient for measurement and record it, and the "V/div" switch and The trim knob position remains 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 time, the output amplitude of the standard voltage is equal to the amplitude of the measured voltage. The comparison method for measuring voltage can avoid sum errors caused by the vertical system, thus improving the measurement accuracy.