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Fundamentals of Measurement: Transducers and Instrumentation, Lecture notes of Electronics

This lecture introduces the concept of measurement, focusing on physical quantities and the measurement process. It covers various types of measurements, fundamental measuring processes, measurement systems, and the difference between measured and true values. The lecture also discusses static characteristics of measurement systems, including accuracy, precision, resolution, threshold, static sensitivity, and hysteresis.

Typology: Lecture notes

2019/2020

Uploaded on 04/03/2020

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Transducers and Instrumentation
Lecture 1
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Transducers and Instrumentation

Lecture 1

Measurement

  • Measurements provide us with a means of describing various phenomena in quantitative terms.
  • "whatever exists, exists in some amount".
  • The determination of the amount is measurement all about.

Fundamental Measuring Process

Measurement System

  • Measurement systems are used for many detailed purposes in a wide variety of application areas.
  • The term “measurement system” is meant to include all components in a chain of hardware and software that leads from the measured variable to processed data.

Reference Value

  • Exemplar Method
    • The method agreed on by experts as being sufficiently accurate for the purposes to which the data will ultimately be put.
  • True value is then referred to as Reference Value when measured by an exemplar method

Nature of Measurement Process

  • Measurement process, with assumed identical conditions, repeated over and over, will not produce the same output(s) always. - Never possible to ensure identical conditions for each trial
  • Random Sequence-in state of statistical control
  • For future use, numerical estimates of error associated with collected data set can be calculated

Bias and Uncertainty in Measurement

Performance Characteristics

  • Selection of most suitable instrument
    • (proposed measurement)
  • Design of Instrument
    • (For specific measuring tasks)
  • Performance Criteria
    • Quantitative bases for comparing one instruments with possible alternatives

Static Characteristics

  • Accuracy
    • closeness of the instrument output to the true value of the measured quantity
    • 1 g with an error of 10
      • 2 g
    • inherent limitations of the instrument
    • shortcomings in the measurement process
    • systematic or cumulative errors

Static Characteristics

  • Precision
    • ability of the instrument to reproduce a certain set of readings within a given accuracy
    • Repeatability of same measured quantity, made by the same observer, using the same instrument, under the same conditions.
    • Random or accidental errors
    • Determine extent of random errors using Statistical analysis

Static Characteristics

  • Resolution
    • smallest increment in the measured value detected with certainty by the instrument.
    • Degree of fineness with which a measurement
  • Threshold
    • minimum value of input below which no output can be detected.
    • friction between moving parts
    • looseness in joints (more correctly termed as backlash),
    • inertia of the moving parts
    • length of the scale,
    • spacing of graduations,
    • size of the pointer, etc.

Static Characteristics

  • Static Sensitivity (Gain/Scale factor)
    • determined from the results of static calibration
    • sensitivity is represented by the slope of the input-output curve
    • sensitivity of a typical linear spring 400N/mm
    • Deflection factor

Drift

  • It is defined as the variation of output for a given input caused due to change in the sensitivity of the instrument due to certain interfering inputs like temperature changes, component instabilities, etc.

Linearity

  • Desirable Feature
    • Linear indicating scale
  • Departure from linearity
  • Independent of input
  • Proportional to input