PE2-4.1 Measurement Characteristics & Error Analysis
You can distinguish sensor from transducer, specify range, resolution, sensitivity, repeatability, linearity, accuracy, impedance, backlash, response time and dead band, and classify and propagate measurement errors.
This unit is the discipline behind every number the rest of the course produces, and the distinction that matters most is systematic versus random error: random error you can average away, systematic error survives any number of repetitions. Error propagation is the practical skill — when a result combines several measurements, the uncertainties combine too, and usually the worst single instrument dominates. Loading effect is the subtle one: the act of measuring changes what you are measuring.
Work through these
Difference between a sensor and a transducer; primary measuring elements
Two words used interchangeably in conversation and distinguished here. Getting the distinction right makes the classification in the next topic coherent.
Range, resolution and sensitivity
The first three specification numbers, and what each actually promises. Sensitivity is the one most often confused with resolution.
Repeatability, linearity and accuracy
Three more, and the pair people conflate most: accuracy is about truth, repeatability is about consistency. A device can be one without the other.
Impedance, backlash, response time and dead band
Four properties that describe how the device behaves in a system rather than alone. Dead band is the one that surprises people in control applications.
Absolute error, relative error and limiting errors
How error is quoted, and why the relative form is usually the useful one. Limiting error is what a manufacturer actually guarantees.
Propagation of errors
What happens to error when measurements are combined in a calculation. It is the item that decides whether a measurement chain meets its specification.
Gross, systematic and random errors
The three kinds of error and, importantly, what can be done about each. Systematic error can be corrected and random error cannot, which is the whole point.
Loading effect
The measurement changing what it measures, which is the error people forget entirely. It is why input impedance appears in the item above.
Statistical analysis of measurement data and probable error
Treating repeated measurements statistically, which is how random error is quantified. It closes the topic by turning the vocabulary into numbers.
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