How the low inductance of short ground clip probes prevents interference?











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1
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Below are photos of two scope probes with different ground clip lengths:



enter image description here



enter image description here



I have read that the shorter ground is used to minimize the inductance of the probe ground lead.



But what does that help for? What happens when the inductance of the ground lead is low? What kind of interference it prevents?






oscilloscope probe







share|improve this question


















  • 1




    flip the question, what is going to happen when the inductance of the ground lead is high.
    – JonRB
    6 hours ago










  • Is the long lead related to picking up conducted or radiated interference?
    – user1234
    6 hours ago






  • 1




    I'll go to bed now, but as I explained in my answer, a series inductance doesn't allow high-frequency ground currents to balance through the probe. If you do high-speed measurements with an oscilloscope, you will need to understand what impedance is!
    – Marcus Müller
    6 hours ago






  • 1




    @user1234 and, as I literally said in my answer, no, it doesn't pick up interference.
    – Marcus Müller
    6 hours ago






  • 1




    exactly. and now one part of the measurement path has a higher impedance for the supply spike to travel.
    – Marcus Müller
    6 hours ago















up vote
1
down vote

favorite












Below are photos of two scope probes with different ground clip lengths:



enter image description here



enter image description here



I have read that the shorter ground is used to minimize the inductance of the probe ground lead.



But what does that help for? What happens when the inductance of the ground lead is low? What kind of interference it prevents?






oscilloscope probe







share|improve this question


















  • 1




    flip the question, what is going to happen when the inductance of the ground lead is high.
    – JonRB
    6 hours ago










  • Is the long lead related to picking up conducted or radiated interference?
    – user1234
    6 hours ago






  • 1




    I'll go to bed now, but as I explained in my answer, a series inductance doesn't allow high-frequency ground currents to balance through the probe. If you do high-speed measurements with an oscilloscope, you will need to understand what impedance is!
    – Marcus Müller
    6 hours ago






  • 1




    @user1234 and, as I literally said in my answer, no, it doesn't pick up interference.
    – Marcus Müller
    6 hours ago






  • 1




    exactly. and now one part of the measurement path has a higher impedance for the supply spike to travel.
    – Marcus Müller
    6 hours ago













up vote
1
down vote

favorite









up vote
1
down vote

favorite











Below are photos of two scope probes with different ground clip lengths:



enter image description here



enter image description here



I have read that the shorter ground is used to minimize the inductance of the probe ground lead.



But what does that help for? What happens when the inductance of the ground lead is low? What kind of interference it prevents?






oscilloscope probe







share|improve this question













Below are photos of two scope probes with different ground clip lengths:



enter image description here



enter image description here



I have read that the shorter ground is used to minimize the inductance of the probe ground lead.



But what does that help for? What happens when the inductance of the ground lead is low? What kind of interference it prevents?






oscilloscope probe




oscilloscope probe






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 6 hours ago









user1234

1




1








  • 1




    flip the question, what is going to happen when the inductance of the ground lead is high.
    – JonRB
    6 hours ago










  • Is the long lead related to picking up conducted or radiated interference?
    – user1234
    6 hours ago






  • 1




    I'll go to bed now, but as I explained in my answer, a series inductance doesn't allow high-frequency ground currents to balance through the probe. If you do high-speed measurements with an oscilloscope, you will need to understand what impedance is!
    – Marcus Müller
    6 hours ago






  • 1




    @user1234 and, as I literally said in my answer, no, it doesn't pick up interference.
    – Marcus Müller
    6 hours ago






  • 1




    exactly. and now one part of the measurement path has a higher impedance for the supply spike to travel.
    – Marcus Müller
    6 hours ago














  • 1




    flip the question, what is going to happen when the inductance of the ground lead is high.
    – JonRB
    6 hours ago










  • Is the long lead related to picking up conducted or radiated interference?
    – user1234
    6 hours ago






  • 1




    I'll go to bed now, but as I explained in my answer, a series inductance doesn't allow high-frequency ground currents to balance through the probe. If you do high-speed measurements with an oscilloscope, you will need to understand what impedance is!
    – Marcus Müller
    6 hours ago






  • 1




    @user1234 and, as I literally said in my answer, no, it doesn't pick up interference.
    – Marcus Müller
    6 hours ago






  • 1




    exactly. and now one part of the measurement path has a higher impedance for the supply spike to travel.
    – Marcus Müller
    6 hours ago








1




1




flip the question, what is going to happen when the inductance of the ground lead is high.
– JonRB
6 hours ago




flip the question, what is going to happen when the inductance of the ground lead is high.
– JonRB
6 hours ago












Is the long lead related to picking up conducted or radiated interference?
– user1234
6 hours ago




Is the long lead related to picking up conducted or radiated interference?
– user1234
6 hours ago




1




1




I'll go to bed now, but as I explained in my answer, a series inductance doesn't allow high-frequency ground currents to balance through the probe. If you do high-speed measurements with an oscilloscope, you will need to understand what impedance is!
– Marcus Müller
6 hours ago




I'll go to bed now, but as I explained in my answer, a series inductance doesn't allow high-frequency ground currents to balance through the probe. If you do high-speed measurements with an oscilloscope, you will need to understand what impedance is!
– Marcus Müller
6 hours ago




1




1




@user1234 and, as I literally said in my answer, no, it doesn't pick up interference.
– Marcus Müller
6 hours ago




@user1234 and, as I literally said in my answer, no, it doesn't pick up interference.
– Marcus Müller
6 hours ago




1




1




exactly. and now one part of the measurement path has a higher impedance for the supply spike to travel.
– Marcus Müller
6 hours ago




exactly. and now one part of the measurement path has a higher impedance for the supply spike to travel.
– Marcus Müller
6 hours ago










2 Answers
2






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up vote
3
down vote













It doesn't prevent interference. It prevents ground lead impedance.



Simply imagine an inductor in series with your ground connection: that acts as a low-pass filter. So, high-speed currents can't be grounded, and for these, your instrument seems to float.






share|improve this answer




























    up vote
    2
    down vote













    I was invited to assist in debugging a switching regulator IC; problem was "two kinds of oscillation".



    I asked what were the frequency of oscillation, and answer was 80MHz.



    I asked "how long is the scope ground lead" with answer being "The usual 6inches or 8inches".



    I explained "The resonant frequency, of 200nH (8") gnd-lead scope probe with 15pF input capacity, is about 90MHz."



    Turns out the silicon designer had cranked out LDOs in his prior IC work, and had never needed to learn fast transient probing methods. Here he got to learn about scope probe ringing.



    The other form of oscillation/noise/weird-behavior involved jitter in the timing of entering and exiting discontinuous modes. That involved very very slow decays of the regulated voltage and timing errors caused by thermal noise.






    share|improve this answer





















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      2 Answers
      2






      active

      oldest

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      2 Answers
      2






      active

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      active

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      active

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      up vote
      3
      down vote













      It doesn't prevent interference. It prevents ground lead impedance.



      Simply imagine an inductor in series with your ground connection: that acts as a low-pass filter. So, high-speed currents can't be grounded, and for these, your instrument seems to float.






      share|improve this answer

























        up vote
        3
        down vote













        It doesn't prevent interference. It prevents ground lead impedance.



        Simply imagine an inductor in series with your ground connection: that acts as a low-pass filter. So, high-speed currents can't be grounded, and for these, your instrument seems to float.






        share|improve this answer























          up vote
          3
          down vote










          up vote
          3
          down vote









          It doesn't prevent interference. It prevents ground lead impedance.



          Simply imagine an inductor in series with your ground connection: that acts as a low-pass filter. So, high-speed currents can't be grounded, and for these, your instrument seems to float.






          share|improve this answer












          It doesn't prevent interference. It prevents ground lead impedance.



          Simply imagine an inductor in series with your ground connection: that acts as a low-pass filter. So, high-speed currents can't be grounded, and for these, your instrument seems to float.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 6 hours ago









          Marcus Müller

          30.8k35691




          30.8k35691
























              up vote
              2
              down vote













              I was invited to assist in debugging a switching regulator IC; problem was "two kinds of oscillation".



              I asked what were the frequency of oscillation, and answer was 80MHz.



              I asked "how long is the scope ground lead" with answer being "The usual 6inches or 8inches".



              I explained "The resonant frequency, of 200nH (8") gnd-lead scope probe with 15pF input capacity, is about 90MHz."



              Turns out the silicon designer had cranked out LDOs in his prior IC work, and had never needed to learn fast transient probing methods. Here he got to learn about scope probe ringing.



              The other form of oscillation/noise/weird-behavior involved jitter in the timing of entering and exiting discontinuous modes. That involved very very slow decays of the regulated voltage and timing errors caused by thermal noise.






              share|improve this answer

























                up vote
                2
                down vote













                I was invited to assist in debugging a switching regulator IC; problem was "two kinds of oscillation".



                I asked what were the frequency of oscillation, and answer was 80MHz.



                I asked "how long is the scope ground lead" with answer being "The usual 6inches or 8inches".



                I explained "The resonant frequency, of 200nH (8") gnd-lead scope probe with 15pF input capacity, is about 90MHz."



                Turns out the silicon designer had cranked out LDOs in his prior IC work, and had never needed to learn fast transient probing methods. Here he got to learn about scope probe ringing.



                The other form of oscillation/noise/weird-behavior involved jitter in the timing of entering and exiting discontinuous modes. That involved very very slow decays of the regulated voltage and timing errors caused by thermal noise.






                share|improve this answer























                  up vote
                  2
                  down vote










                  up vote
                  2
                  down vote









                  I was invited to assist in debugging a switching regulator IC; problem was "two kinds of oscillation".



                  I asked what were the frequency of oscillation, and answer was 80MHz.



                  I asked "how long is the scope ground lead" with answer being "The usual 6inches or 8inches".



                  I explained "The resonant frequency, of 200nH (8") gnd-lead scope probe with 15pF input capacity, is about 90MHz."



                  Turns out the silicon designer had cranked out LDOs in his prior IC work, and had never needed to learn fast transient probing methods. Here he got to learn about scope probe ringing.



                  The other form of oscillation/noise/weird-behavior involved jitter in the timing of entering and exiting discontinuous modes. That involved very very slow decays of the regulated voltage and timing errors caused by thermal noise.






                  share|improve this answer












                  I was invited to assist in debugging a switching regulator IC; problem was "two kinds of oscillation".



                  I asked what were the frequency of oscillation, and answer was 80MHz.



                  I asked "how long is the scope ground lead" with answer being "The usual 6inches or 8inches".



                  I explained "The resonant frequency, of 200nH (8") gnd-lead scope probe with 15pF input capacity, is about 90MHz."



                  Turns out the silicon designer had cranked out LDOs in his prior IC work, and had never needed to learn fast transient probing methods. Here he got to learn about scope probe ringing.



                  The other form of oscillation/noise/weird-behavior involved jitter in the timing of entering and exiting discontinuous modes. That involved very very slow decays of the regulated voltage and timing errors caused by thermal noise.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 55 mins ago









                  analogsystemsrf

                  13.2k2716




                  13.2k2716






























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