When using an oscilloscope probe to measure the AC waveform between the two ends of a component, how should the probe ground wire be connected?

深圳小花

When using an oscilloscope probe to measure the AC waveform between the two ends of a component, how should the probe ground wire be connected? [Copy link]

 

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When using an oscilloscope probe to measure the AC waveform between the two ends of a component, if the peak value of the AC voltage of the probe ground wire is 180V and the minimum value is -180V, the peak value of the probe is 210V and the minimum value is -210V, because the probe is actually connected to the neutral wire and the ground wire, it seems that it cannot be measured. How do you measure it?

maychang

"Because the probe is actually connected to the neutral wire and the ground wire, it seems that it cannot be measured."

It is indeed impossible to measure.

深圳小花

maychang posted on 2021-7-22 08:48 "Because the probe is actually connected to the neutral wire and the ground wire, it seems that it cannot be measured." It is indeed impossible to measure.

Thank you so much.

maychang

"How do you measure it?"

If both ends of the component have very low impedance to the circuit "ground" and the oscilloscope case is not grounded, then a single ordinary probe can be used for measurement. The probe ground lead clip is clamped on one end of the component and the probe touches the other end.

But it is best not to do this. First, it is dangerous, and second, the measurement results are inaccurate.

maychang

"How do you measure it?"

Some dual-trace oscilloscopes have an inverting switch on one channel. If we use two probes, the ground clips are both grounded (the common point of the circuit), the two probes are placed at both ends of the component to be measured, and the oscilloscope Y-axis gain is adjusted to the same for both channels, then the waveform displayed by the oscilloscope is the difference between the voltages of the two channels, that is, the voltage at both ends of the component.

Some dual-trace oscilloscopes can directly display the difference between the two channel signals, which is even more convenient.

maychang

If you have a differential probe, it is certainly more convenient and can be measured directly. However, differential probes are expensive.

maychang

The oscilloscope housing is usually connected to the ground through a three-pin power plug, so when making any measurements, you must pay attention to whether there is voltage between the "ground" of the circuit to be tested and the ground.

Gen_X

I have an oscilloscope similar to yours.

There are two channels, one of which is the same as you.

The main reason is that there is an AC "common mode" capacitor between the shielding layer of the probe and the AC ground, and this capacitor has broken down. I cannot replace it myself.

Therefore, your oscilloscope cannot be used in this case.

In addition, general oscilloscope probes have attenuation. If your signal is too large, you can use X10 to measure it.

深圳小花

maychang published on 2021-7-22 09:01 The oscilloscope housing is usually connected to the ground through a three-pin power plug, so when making any measurements, please note that the "ground" of the circuit to be tested is...

Thank you very much. Is the ground clip of the probe directly connected to the oscilloscope case? Is it connected to the neutral line of the oscilloscope?

深圳小花

Gen_X posted on 2021-7-22 09:58 I have an oscilloscope like yours. It has two channels, one of which is the same as yours. The main reason is the shielding layer of the probe and the AC ground...

Thank you very much. Is the ground clip of the probe directly connected to the oscilloscope case? Is it connected to the neutral line of the oscilloscope?

AC ground? Isn't it the neutral line of AC? What is AC ground?

maychang

Shenzhen Xiaohua published on 2021-7-22 10:43 Thank you very much. Is the grounding clip of the probe directly connected to the housing of the oscilloscope? Is it connected to the neutral line of the oscilloscope? ...

"Excuse me, is the ground clip of the probe directly connected to the oscilloscope's housing? Is it connected to the oscilloscope's neutral line?"

I know the answer to your question, but I strongly recommend that you get a multimeter and measure it yourself.

深圳小花

maychang posted on 2021-7-22 11:00 "Excuse me, is the ground clip of the probe directly connected to the housing of the oscilloscope? Is it connected to the neutral wire of the oscilloscope? 』 I know...

OK, thanks.