Hardware test - why not use grounding clip for ripple test

Today, let's briefly talk about why we can't use the grounding clip when using an oscilloscope to test the ripple of a single board , If you say something wrong, you can point it out , Learn from the experience of your peers , The following figure shows the standard grounding clip of oscilloscope probe .

I believe that most people in this industry have consulted or taught by teachers to accurately measure the ripple of power quality. Do not use grounding clamps , The standard probe requires the use of grounding spring, etc , Basically, the loop formed by the grounding clamp and the probe of the probe will be subject to external interference to introduce noise and affect the test results , Today is to verify why the test results using grounding clamps are inaccurate . Here a Tektronix is used MDO4104C The oscilloscope of , Standard configuration X10 1G Passive probe , Use the grounding spring and grounding wire to test the ripple respectively .

 

The parameter configuration of oscilloscope is not specified here ：

The coupling mode is AC .

Bandwidth throttling on 20M

Because the probe itself is X10 Of cannot be adjusted , Use X10 Test in gear .

First use the grounding clip to test , The grounding clip is connected GND Line , The probe is connected to the positive pole of the capacitor at the test point .

Adjust the oscilloscope for observation , There is a... To observe the ripple 400KHz Left and right noise .

  When using the grounding spring to test the ripple , The grounding spring is connected to the negative pole of the test capacitor , Positive pole of probe capacitance .

Observe that the measured ripple is not periodic 400Khz The noise of , The peak and peak values also decreased .

 ps（ The negative pole test of the grounding clamp connected to the capacitor also exists 400Khz Periodic noise on the left and right ）.

The above is a brief test record , Relatively simple , Engaged in hardware industry , A lot of them are searching for information 、 Videos and so on to learn and supplement knowledge , It would be great if there were more professional people to give advice and exchange . Limited ability , Hope not to mislead beginners .