Method and precautions for measuring voltage with oscilloscope

Oscilloscope is a commonly used measuring instrument, mainly used for detecting various electrical signals, and has certain applications in fields such as power, electronics, medicine, and scientific research. Have we learned about the methods and precautions for measuring pressure when using an oscilloscope? Below, the editor will introduce the pressure measurement method and precautions of oscilloscope in detail, hoping to help everyone.

1、 The method of measuring voltage with oscilloscope

1. Direct measurement method

The so-called direct measurement method is to directly measure the height of the measured voltage waveform from the screen and then convert it into a voltage value. When quantitatively testing voltage, the fine adjustment knob of the Y-axis sensitivity switch is generally turned to the "calibration" position, so that the measured voltage value can be directly calculated from the indicated value of "V/div" and the vertical axis coordinate value occupied by the measured signal. So, the direct measurement method is also known as the ruler method.

(1) Measurement of DC voltage

Place the Y-axis input coupling switch in the "ground" position and the trigger mode switch in the "automatic" position, so that the screen displays a horizontal scanning line, which is the zero level line.

Set the Y-axis input coupling switch to the "DC" position and add the measured voltage. At this point, the scanning line produces 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 easy to implement, but the error is relatively large. The factors that cause errors include reading errors, parallax, and oscilloscope system errors (attenuators, deflection systems, oscilloscope edge effects).

(2) Measurement of AC voltage

Place the Y-axis input coupling switch in the "AC" position to display the AC component of the input waveform. When the frequency of the communication signal is very low, the Y-axis input coupling switch should be placed in the "DC" position.

Move the measured waveform to the center position 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 degree H of the entire waveform in the Y-axis direction according to the division of the coordinate scale. 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 using a probe for measurement, the attenuation of the probe should be taken into account by multiplying the calculated value by 10.

For example, if the Y-axis sensitivity switch "V/div" of an oscilloscope is located at the 0.2 level, 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 is 1V. If it is measured by a probe and still indicates the above value, then the peak to peak value of the measured signal voltage is 10V.

2. Comparative measurement method

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 adjustment knob, so that the fluorescent screen displays the height Hx that is easy to measure and records it, while keeping the position of the "V/div" switch and fine adjustment knob unchanged.

Remove the measured voltage, input a known adjustable standard voltage Vs into the Y-axis, 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 comparative method for measuring voltage can avoid errors caused by vertical systems, thus improving measurement accuracy.

2、 Precautions for using oscilloscope

For the safety of instrument operators and instrument safety, the instrument should work normally within a safe range to ensure accurate measurement waveforms and reliable data. Attention should be paid to:

1. If users need to measure products such as switch power supplies (primary switch power supplies, control circuits), UPS (uninterruptible power supplies), electronic rectifiers, energy-saving lamps, frequency converters, or other electronic devices that cannot be isolated from the mains AC220V for floating signal testing, they must use DP100 high-voltage isolation differential probes.

2. A universal oscilloscope adjusts the brightness and focus knob to minimize the diameter of the light spot, making the waveform clear and reducing testing errors; Do not keep the light spot stationary at any point, otherwise the electron beam hitting a point will form dark spots on the fluorescent screen and damage it.

The casing of a universal oscilloscope, the BNC socket metal outer ring of the signal input terminal, the probe grounding wire, and the AC220V power socket grounding wire are all interconnected. If the instrument is not connected to the ground wire during use and the floating ground signal is directly measured with a probe, a potential difference will be generated between the instrument and the ground; The voltage value is equal to the potential difference between the probe grounding wire contact point of the tested equipment and the ground. This will pose serious safety hazards to instrument operators, oscilloscopes, and tested electronic devices.

4. Measurement systems - such as oscilloscopes, signal sources; Devices such as printers and computers. The grounding wire of the tested electronic equipment, such as instruments, electronic components, circuit boards, and the power supply of the tested equipment, must be connected to the common ground (earth).