EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Cliff Matthews on May 20, 2020, 11:36:02 am
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New W2AEW #311 video describes the top 5 reasons that you might think your oscilloscope voltage readings are wrong.
https://www.youtube.com/watch?v=nV0BADdBIXw (https://www.youtube.com/watch?v=nV0BADdBIXw)
PDF Notes: https://www.qsl.net/w2aew/youtube/WhyScopeReadingWrong.pdf (https://www.qsl.net/w2aew/youtube/WhyScopeReadingWrong.pdf)
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:
https://www.youtube.com/watch?v=SX4HGNWBe5M (https://www.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:
https://www.youtube.com/watch?v=tClE8s6RZdg (https://www.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:
https://www.youtube.com/watch?v=eRA1Mx506fw (https://www.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:
https://www.youtube.com/watch?v=oZ1Dv2dVGkU (https://www.youtube.com/watch?v=oZ1Dv2dVGkU)
https://www.youtube.com/watch?v=hXbPnY7VIes (https://www.youtube.com/watch?v=hXbPnY7VIes)
https://www.youtube.com/watch?v=Ly5pmYopEfU (https://www.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:
https://www.youtube.com/watch?v=oxJQr4dKnys (https://www.youtube.com/watch?v=oxJQr4dKnys)