How to estimate the measurement uncertainty of an oscilloscope ?

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Discussion Overview

The discussion revolves around estimating the measurement uncertainty of a Tektronix oscilloscope, specifically the DPO7054 or DPO7254 models. Participants are exploring how to interpret the information provided in the calibration sheet and manual regarding measurement uncertainty, particularly in relation to pulse area measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about how to determine measurement uncertainty from the calibration sheet, which provides values in divisions rather than percentages.
  • Another participant requests the model number of the oscilloscope to provide more specific assistance.
  • It is noted that the datasheet contains accuracy specifications, but the original poster still struggles to apply this information to calculate measurement uncertainty for pulse area.
  • A participant suggests that to estimate uncertainty, one might need to combine error specifications for vertical amplitude and horizontal time base jitter, while also asking for additional details about the application and signal characteristics.
  • Reference is made to the user manual, indicating that vertical accuracy varies with frequency and can be quantified in terms of effective bits, with a specific calculation provided for a 2.5 GHz scenario.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on how to calculate measurement uncertainty, with multiple viewpoints and approaches being discussed. The original poster's confusion remains unresolved, and there is no agreement on a definitive method.

Contextual Notes

The discussion highlights limitations in the provided documentation, such as the lack of clear guidance on measurement uncertainty in the manual and calibration sheet. There are also unresolved questions regarding the specific application and signal characteristics relevant to the uncertainty calculation.

nordmoon
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TL;DR
How to estimate the measurement uncertainty of an Textronics 500 MHz oscilloscope ?
I have an Textronics oscilloscope with 500 MHz sampling rate and using an 50 ohm cable for the measurement.

I can’t find the measurement uncertainty in the manual or the calibration sheet.

In the calibration sheet it says an ‘uncertainty’ for the used channel in divisions, for example 1m up to 10m (the scale) and with highest value being 1. It states the nominal value, upper and lower value and the measurement value. It also state an uncertainty (value between 1-2m) but not in %. I don’t understand how to determine the measurement uncertainty from this data. Anyone understand this?

The manual is even more cryptic .. no words on measurement uncertainty.
 
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Do you have a model number?
 
Averagesupernova said:
Do you have a model number?

If I remember correctly it’s a DPO7054 or DPO7254.
 
nordmoon said:
Yes but I don’t understand how to determine the measurement uncertainty, for the measured pulse area, with this oscilloscope ?
Pulse area? Are you checking Eye Diagrams for communication circuits? What is the application?

I would think that you would combine the error specs for the vertical amplitude and horizontal time base jitter, but maybe there are other considerations. What frequency and rise/fall times are involved? What range of voltage amplitudes?
 
In the manual, for vertical accuracy see Appendix A, page A-8 "Effective bits, typical." Depending on frequency, the accuracy ranges between 5.2 and 6 bits.

Therefore, at 2.5GHz the vertical accuracy would be:
1/(25.2) = 1/36.76 = 2.7% of Full Scale reading

User Manual .pdf is available at:
https://download.tek.com/manual/071087903.pdf

Cheers,
Tom
 
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