Measuring uncertainty spec for an oscilloscope?

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Discussion Overview

The discussion revolves around calculating uncertainty measurements for oscilloscopes, particularly focusing on how to interpret the specification of '1/2 the smallest division' in the context of both vertical and horizontal scales. Participants explore the implications of this measurement in experimental setups.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about which 'division' the uncertainty measurement refers to, questioning whether it applies to vertical or horizontal scales, and suggests that with a vertical scale set to 2 volts per division, the uncertainty might be 1 volt.
  • Another participant asks for the oscilloscope's manufacturer and model number, indicating that consulting the manual could provide clarity on the uncertainty measurement.
  • A different participant proposes that the time base accuracy is likely specified separately in the manual, suggesting that uncertainty is primarily related to the signal when measuring one channel.
  • One participant elaborates on the historical context of CRT oscilloscopes, explaining that older models used centimeter squares as divisions, and notes that an error of half a subdivision corresponds to ±5% of the setting, providing an example with a 2V/div range resulting in an error of ±0.1 V.
  • Another participant comments on the calibration of divisions in modern oscilloscopes, suggesting that 5 minor divisions per centimeter is more common now, while reiterating the importance of referring to the manual or datasheet for clarification.

Areas of Agreement / Disagreement

Participants express varying levels of uncertainty regarding the interpretation of 'division' in the context of uncertainty measurement. There is no consensus on the specifics of the measurement or its application, and multiple viewpoints are presented without resolution.

Contextual Notes

Participants highlight the potential for confusion due to different scaling methods in oscilloscopes and the need for specific model information to accurately determine uncertainty. The discussion reflects a lack of clarity on how to apply the uncertainty measurement across different settings.

superstrings
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I just started learning about oscilloscopes and I am confused on how to calculate the uncertainty. The uncertainty measurement on the device says '1/2 the smallest division'.

I am unsure which 'division' this refers to since there are horizontal scales and vertical scales.
In my experiment I had the vertical scale set to 2 volts per div, so would the uncertainty then be 1 volt?
 
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What is the scope manufacturer and model number?
Reading the manual comes in handy when seeking answers to such questions.
 
My bet is you can assume the time base (produced by the oscilloscope, horizontal axis when measuring one channel only) to be sure (or its accuracy will be listed separately in the manual), and the uncertainty is related only to the signal.

This can get more complicated when doing two channel measurements.
 
superstrings said:
I am unsure which 'division' this refers to since there are horizontal scales and vertical scales.
In my experiment I had the vertical scale set to 2 volts per div, so would the uncertainty then be 1 volt?
Older CRT oscilloscopes were calibrated with approximately one centimetre squares. Each of those was called a division. Those divisions were divided again by 10 to give approx 1 mm sub-divisions.

An error of half a subdivision means ±5% of the setting. So on the 2V/div range, the error is ±0.1 V.

There is usually a calibration signal test point on the CRO. Maybe a square-wave 1kHz, 0.1Vpp. Look at that to identify the calibration used for voltage and time.
 
Baluncore said:
Older CRT oscilloscopes were calibrated with approximately one centimetre squares. Each of those was called a division. Those divisions were divided again by 10
In think that 5 minor divisions per centimeter is more common now. So that's what I'd guess the specification the OP is referring to means (although as pointed out, it would be good to have a link to the manual/datasheet the OP is referring to).

http://www.hobbyprojects.com/oscilloscope_tutorial/images/display_of_oscilloscope.gif
display_of_oscilloscope.gif
 
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