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lecture2.pdf

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Alex Liberzon

This document outlines topics related to engineering testing and measurements. It discusses types of signals, sensors, and transducers including displacement sensors, zero displacement sensors, direct and indirect sensors, and passive and active sensors. It also covers errors, accuracy, and precision in measurements and defines related terms like error, accuracy, precision, bias, and signal-to-noise ratio. Additionally, it lists topics that will be covered including backup of measurement systems, calibration and associated errors, regression analysis, and log-log calibration.

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Engineering Testing and Measurements Alex Liberzon Tel Aviv University March 22, 2014
Outline 1. Backup of the measurement system, types of signals 2. errors vs uncertainty 3. Calibration and calibration errors 4. Regression 5. Log-log 6. calibration errors
Generalized measurement system
Types of sensors/transducers Displacement type of sensors - the change in the measured quantity causes a change of the sensor/transducer and creates a proportional signal. Zero displacement sensor - a change of some quantity through the closed loop control adjusts the sensing point Advantages: very small deviations can be measured as these are amplified by the control loop (passive or active) and it is easy to compare the signal to the zero value. Disadvantages: frequency f [Hz] or the time response [sec] of the control loop affects the sampling frequency, fs
Types of sensors/transducers Direct sensor- the sensor reacts directly to the quantity measured, e.g. weight is measured by calibrated weight balance. Indirect sensor - the sensor reacts to another quantity rather than the measured one and we can infer the measured quantity by some physical law, e.g. change of electrical resistance indicates the change of temperature of the resistor. Passive sensor - the only energy is from the measurement, e.g. temperature measurement by the thermocouple Active sensor - receives energy from external source, e.g. piezo-electric pressure transducer, hot-wire
Types of signals Analog: precise value is important, physical quantities like length, voltage, temperature Digital: a combination of N bits (0/1 or On/Off), no precise value, less sensitive to analog noise, but limited resolution = FOS/2N
Sensitivity
Error, accuracy, precision Error: difference e between the measurement x and the true value x0: e = |x x0| Accuracy: the ratio of error e to the true value or to some other reference, e.g. a = e x 100% a = e xmax xmin = e xf 100% percents of the value or percents of the full-scale Precision, reproducibility: capability of the system to return the same value
Example The known value is 100, we measured: 103, 104, 105, 103, 105 the errror: e = 5, accuracy = 5% , precision: 賊1 around the mean value of 104 bias, systematic error: 104 - 100
Signal-to-noise ratio: A/B
Full calibration analysis

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lecture2.pdf

  • 1. Engineering Testing and Measurements Alex Liberzon Tel Aviv University March 22, 2014
  • 2. Outline 1. Backup of the measurement system, types of signals 2. errors vs uncertainty 3. Calibration and calibration errors 4. Regression 5. Log-log 6. calibration errors
  • 4. Types of sensors/transducers Displacement type of sensors - the change in the measured quantity causes a change of the sensor/transducer and creates a proportional signal. Zero displacement sensor - a change of some quantity through the closed loop control adjusts the sensing point Advantages: very small deviations can be measured as these are amplified by the control loop (passive or active) and it is easy to compare the signal to the zero value. Disadvantages: frequency f [Hz] or the time response [sec] of the control loop affects the sampling frequency, fs
  • 5. Types of sensors/transducers Direct sensor- the sensor reacts directly to the quantity measured, e.g. weight is measured by calibrated weight balance. Indirect sensor - the sensor reacts to another quantity rather than the measured one and we can infer the measured quantity by some physical law, e.g. change of electrical resistance indicates the change of temperature of the resistor. Passive sensor - the only energy is from the measurement, e.g. temperature measurement by the thermocouple Active sensor - receives energy from external source, e.g. piezo-electric pressure transducer, hot-wire
  • 6. Types of signals Analog: precise value is important, physical quantities like length, voltage, temperature Digital: a combination of N bits (0/1 or On/Off), no precise value, less sensitive to analog noise, but limited resolution = FOS/2N
  • 8. Error, accuracy, precision Error: difference e between the measurement x and the true value x0: e = |x x0| Accuracy: the ratio of error e to the true value or to some other reference, e.g. a = e x 100% a = e xmax xmin = e xf 100% percents of the value or percents of the full-scale Precision, reproducibility: capability of the system to return the same value
  • 9. Example The known value is 100, we measured: 103, 104, 105, 103, 105 the errror: e = 5, accuracy = 5% , precision: 賊1 around the mean value of 104 bias, systematic error: 104 - 100
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