A "10X" passive probe attenuates the signal by a factor of 10, but it
also reduces the load it places on your circuit by a factor of 10.
It's called "10X" because in the very old days, you had to multiply
whatever the scope said by 10. The probe divides the voltage. You do
the multiply. If these modern times, digital oscilloscopes either
automatically detect which probe you're using (usually by a resistor
connected to a spring-loaded pin in the probe that touches an outer ring
where it plugs into your scope) or by manual setting for cheaper probes
and scopes without automatic probe detection, so the measurements you
see are always the real voltage.
For most tasks, 1/10th the measurement resolution is a good trade-off
for less circuit loading. If you go poking around sensitive analog
circuits with a 1X probe, you'll often make pretty substantial changes
to what you're trying to measure. Even a 10X probe has its limitations,
but they're only 1/10th as troublesome. Still, you should be aware
you're poking around with a 10M resistor in parallel with some
capacitor, probably between 10 to 20 pF. The better & more expensive
probes have more bandwidth and lower load capacitance.
Assuming the probe itself is well made, a 10X probe lets you measure a
much wider range. When you measure 240 volts, the probe is dividing it
by 10, so only 24 volts is ending up at the scope input amplifier. Do
not touch stuff over 30V with a 1X probe.
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