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For a university physics experiment, I built a circuit to test voltage (and conductance) steps across a nanowire break junction. The break junction was in a circuit with an I-V converter, and the I-V output was fed to an oscilloscope. The voltage steps measured matched the theory, however they were all a factor of 10 too large. Is this due to the impedance of the oscilloscope? I can't retrieve the exact model now but it was Tektronix and the standard oscilloscope used across the university, so I assume it is 1MOhm. Is there anything else involving the impedance (or any other factor) that could be causing the factor of 10?

I double checked the I-V contributions of all components in the circuit, such as the feedback resistor in the converter, and couldn't find anything so can only conclude it is the oscilloscope. But electronics is not my forte so I am not sure how an oscilloscope could cause x10 to the voltage.

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    \$\begingroup\$ Most likely a mismatch between the probe setting on the probe and the setting on the scope. \$\endgroup\$ – Scott Seidman Apr 3 at 15:48
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    \$\begingroup\$ It was probably set up to use a x10 probe but you used a normal probe. \$\endgroup\$ – Andy aka Apr 3 at 15:48
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    \$\begingroup\$ @Andyaka I'd call a 10x probe a normal probe and the 1x probe the abnormal one, personally. \$\endgroup\$ – Hearth Apr 3 at 16:15
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    \$\begingroup\$ When I was a lad x1 was normal. \$\endgroup\$ – Andy aka Apr 3 at 16:19
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    \$\begingroup\$ @Andyaka x1? X1? When I were a lad, we were lucky to get x0.01, and t' trace were what our fingers scratched in mud from t' electric shock. You try and tell the young people of today that, and they won't believe you. \$\endgroup\$ – Andrew Morton Apr 3 at 16:56
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Some of the probes used with oscilloscopes incorporate a very high impedance input circuit right at the probe tip. This circuit attenuates the signal by a factor of 10. Some oscilloscopes can automatically recognize whether such a probe, usually called a "ten-to-one" probe, is in use but other oscilloscopes require the user to manually change a setting.

My guess is that your oscilloscope assumed that such a probe was being used when in fact it was not, so the recorded voltages are too large by a factor of 10.

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  • \$\begingroup\$ Does the automatic recognition involve extra contacts where the probe is interfaced to the oscilloscope? I have seen photos where there are several little contacts around the BNC connector, and they do not look like a simple round BNC connector. \$\endgroup\$ – Andrew Morton Apr 3 at 20:02
  • \$\begingroup\$ Yes, there are extra contacts in the BNC connector. \$\endgroup\$ – Elliot Alderson Apr 3 at 20:55

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