w2aew | #311: Why are my oscilloscope voltage readings wrong? Top 5 reasons... @w2aew | Uploaded May 2020 | Updated October 2024, 11 hours ago.
This video describes the top 5 reasons that you might think your oscilloscope voltage readings are wrong. These are the most common mistakes made by new users and professionals alike. They are:
1) Voltages are off by a factor of 10 - usually due to not accounting for 10x probe attenuation. See this video about 1x/10x probes:
youtube.com/watch?v=SX4HGNWBe5M
2) Voltages off by a factor of 2 - usually due to using a signal generator that is expecting a 50 ohm load. See this video for more details:
youtube.com/watch?v=tClE8s6RZdg
3) All voltage readings lower than they should be - usually caused by not putting the volts/div vernier into the Calibrated position. See this video on one reason that this control exists:
youtube.com/watch?v=eRA1Mx506fw
4) High frequency voltage readings low - could be several reasons, but most often due to signal frequencies being too close to the scope/probe rated bandwidth. See these videos on scope bandwidth considerations:
youtube.com/watch?v=oZ1Dv2dVGkU
youtube.com/watch?v=hXbPnY7VIes
youtube.com/watch?v=Ly5pmYopEfU
5) Probed voltage amplitudes are not right - most often caused by improper 10x probe compensation. See this video on the importance of probe compensation:
youtube.com/watch?v=oxJQr4dKnys

Video notes can be found here:
qsl.net/w2aew/youtube/WhyScopeReadingWrong.pdf