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I've heard pros of x10 probe a lot. Now I need to know the cons but I couldn't find a clear explanation. Some people say x1 probe is for small signal. How do you decide either x10 or x1.

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    \$\begingroup\$ the primary con is "the x10 probe does what it's specified to do, I don't want that". \$\endgroup\$ Oct 10 '20 at 15:07
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    \$\begingroup\$ Compare input-referred noise. \$\endgroup\$ Oct 10 '20 at 15:08
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    \$\begingroup\$ The primary drawback, as Spehro hints, is that low amplitude signals, attenuated 20dB, can disappear into the scope's own noise floor. \$\endgroup\$ Oct 10 '20 at 15:19
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The pro is that a 10x probe has 10x the input impedance so will interfere with the signal being measured less. The con is that it is reducing the voltage on your signal by 10x before it reaches the scope so it cannot measure signals with very low amplitudes or measure with noise levels as low as a x1 probe will (your scope introduces noise and if your signal is 10x smaller when it reaches the scope, then the noise of the scope will be 10x bigger than it would otherwise relative to the signal).

But a side benefit of stepping down the voltage by 10x before it reaches your scope is that you can measure signals with a maximum amplitude 10x higher.

Use x1 probe to measure very low amplitude signals in low impedance circuits. Use 10x to measure everything else, especially if the circuit being measured is higher impedance. If your circuit is low amplitude but high impedance...well...that's where it gets tricky.

Use probes more than x10 if you need to measure voltages that are higher than what your scope can accept with either a x1 or x10 probe.

I don't like to use a x1 probe with anything I know will be more than 50V, even though a scope input can typically directly accept 300V for oscilloscope preservation purposes. I use a x100 probe for anything larger than 100V for the same reason. You never know what overshoot might exist in a signal you are measuring.

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  • \$\begingroup\$ At 300V and perhaps even as low as 50V, two X10 or X100 probes and differential input should be used. \$\endgroup\$ Oct 10 '20 at 16:22
  • \$\begingroup\$ @CharlesCowie Yeah, at 100V I use a x100 probe. \$\endgroup\$
    – DKNguyen
    Oct 10 '20 at 16:23
  • \$\begingroup\$ Side note, a 10x probe may not always have 10x the impedance, even if it attenuates by 10. For example an oscilloscope bought some years ago came with probes that had 2.2 Mohm input impedance. However, it is more typical that a 10x probe does have 10Mohm input impedance. \$\endgroup\$
    – Justme
    Oct 14 '20 at 16:59
  • \$\begingroup\$ @Justme How does that work? What was going on there? \$\endgroup\$
    – DKNguyen
    Oct 14 '20 at 21:51
  • \$\begingroup\$ @DKNguyen I don't think it's nothing special. The probe was 500 MHz one. Maybe it relates to the bandwidth somehow. I am unsure but it might have been this or similar probe: farnell.com/datasheets/2349648.pdf \$\endgroup\$
    – Justme
    Oct 14 '20 at 22:01
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A downside is that it divides the voltage by 10 and thus the signal is weaker at scope input. So there is a limit how small signals can be measured, but it depends on the scope. If the amplitude is too low for 10x probe, and if it is known that the dowsides of 1x probes do not prevent measurement, then a 1x probe can be used.

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