Difference between revisions of "Precision"
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* The narrowness of the random distribution in the (nowadays digital and discrete) measurement readout. <br>Usually expressed in standard deviation, FWHM or similar. | * The narrowness of the random distribution in the (nowadays digital and discrete) measurement readout. <br>Usually expressed in standard deviation, FWHM or similar. | ||
* Not(!) the possibly present random distribution in the "real" value. | * Not(!) the possibly present random distribution in the "real" value. | ||
| + | * inverse of random measurement deviation | ||
* The unit of precision (when used in the linguistic sense) is the inverse of the measurement quantity <br>("more precise" <=> higher value of inverse standard deviation) | * The unit of precision (when used in the linguistic sense) is the inverse of the measurement quantity <br>("more precise" <=> higher value of inverse standard deviation) | ||
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* The unit of resolution is: readable steps per unit of measurement quantity | * The unit of resolution is: readable steps per unit of measurement quantity | ||
| − | Precision (of single measurements) can never exceed (be finer than) resolution. | + | Precision (of single measurements**) can never exceed (be finer than) resolution. |
| − | + | '''Accuracy:''' | |
| + | * how near the expectation value comes to a reference value ("true" value) - (a qualitative term?) | ||
| + | * inverse of the systematic measurement deviation | ||
| − | By taking many measurements and averaging them out precision can be improved. | + | If accuracy is low highly precise measurements are consistently wrong.<br> |
| + | An error that can be potentially compensated. | ||
| + | |||
| + | === Lowering bandwidth to increase resolution and precision === | ||
| + | |||
| + | By taking many measurements and averaging them out precision can be improved**. | ||
Measuring this way takes more time so the maximum frequency of measurements (bandwidth) gets lower. This is why noise in measurement readouts falls/(rises) with falling/(rising) bandwidth. | Measuring this way takes more time so the maximum frequency of measurements (bandwidth) gets lower. This is why noise in measurement readouts falls/(rises) with falling/(rising) bandwidth. | ||
Revision as of 20:08, 8 August 2017
Contents
Precision in the context of manipulation with actuators
(TODO: elaborate)
Precision in the context of measurements with sensors
Precision:
- The narrowness of the random distribution in the (nowadays digital and discrete) measurement readout.
Usually expressed in standard deviation, FWHM or similar. - Not(!) the possibly present random distribution in the "real" value.
- inverse of random measurement deviation
- The unit of precision (when used in the linguistic sense) is the inverse of the measurement quantity
("more precise" <=> higher value of inverse standard deviation)
Resolution:
- The size of the steps of the measurement readout (no further sub-steps).
- In case precision is far lower than resolution a one step difference is pretty meaningless.
- The unit of resolution is: readable steps per unit of measurement quantity
Precision (of single measurements**) can never exceed (be finer than) resolution.
Accuracy:
- how near the expectation value comes to a reference value ("true" value) - (a qualitative term?)
- inverse of the systematic measurement deviation
If accuracy is low highly precise measurements are consistently wrong.
An error that can be potentially compensated.
Lowering bandwidth to increase resolution and precision
By taking many measurements and averaging them out precision can be improved**. Measuring this way takes more time so the maximum frequency of measurements (bandwidth) gets lower. This is why noise in measurement readouts falls/(rises) with falling/(rising) bandwidth.
In case of manual averaging over many sub measurements at some point precision hits the resolution limit. Quite a bit before that happens one should start to store the averaged values with a higher resolution. While the new precision must still be higher than the new resolution (fundamental fact), the new higher precision (harbored in the new higher resolution) can exceed the old resolution.
The continuum:
Even a single measurement takes finite time. So it can be seen as an average
over many much shorter sub measurements with much lower precision each.
Higher bandwidth <=> more noise.
This is related to the Heisenberg uncertainty principle.
Note that in mechanical nanosystems at room temperature quantum "noise" can be significantly overpowered by thermal noise.
External links
Wikipedia
- en: Accuracy_and_precision => validity ~ seldom: Exactness
(accuracy ~ seldom: correctness ~ ISO: trueness)
de: Richtigkeit & Präzision => Genauigkeit ~ selten: Exaktheit ~ selten: Validität
(Richtigkeit ~ selten: Akkuratheit)
- Random and systematic errors:
Observational_error; Errors_and_residuals;
de: Zufällige Abweichung & Systematische_Abweichung => Messabweichung
- noise; standard deviation; bandwith
