Metrologia - Sistema de Medição (Parte 2 de 2)

Summary

This video explores key concepts related to measurement instruments, including their characteristic response curves, sensitivity, linearity, and response time. It discusses how different instruments, such as force measuring devices and temperature sensors, respond to stimuli and how these responses can be represented graphically. The importance of properties like repeatability, reproducibility, accuracy, and precision are emphasized. The video also highlights measurement errors, such as hysteresis and linearity errors, and explains how they affect instrument performance. Practical examples and mathematical equations are provided to help viewers understand these concepts and their application in calibration and instrumentation systems.

Takeaways

• 😀 The characteristic response curve of an instrument shows the relationship between the applied stimulus and the response it generates, which can be linear or nonlinear.
• 😀 Sensitivity is the relationship between the applied stimulus and the response, which can vary depending on the design and the type of instrument.
• 😀 Hysteresis error occurs when the response to a stimulus differs depending on whether the stimulus is increasing or decreasing, caused by mechanical factors like gaps in components.
• 😀 The response time of an instrument is the time it takes to stabilize after the stimulus is applied, and it is crucial for ensuring accurate readings within an acceptable tolerance range.
• 😀 Measurement errors are categorized as tendency (systematic error), correction (compensation for systematic error), and random errors (as seen in repeatability and reproducibility).
• 😀 Repeatability refers to how consistent measurements are under the same conditions, while reproducibility considers variations in conditions, such as different operators or environments.
• 😀 Linearity error occurs when the instrument’s response deviates from an ideal straight-line curve, and the difference is measured as the linearity error.
• 😀 Precision indicates low random error and consistency in repeated measurements, whereas accuracy refers to how close the measurements are to the true value, with minimal errors.
• 😀 Maximum error is the total error of an instrument, including both systematic and random errors, and it defines the instrument's reliability over its measurement range.
• 😀 The relative representation of errors or sensitivities is useful for comparing instruments across different ranges and helps determine their efficiency in various applications.

Q & A

What is the characteristic response curve of an instrument?

The characteristic response curve represents how an instrument responds to different stimuli. It plots the relationship between the applied stimulus (e.g., force or temperature) and the response of the instrument (e.g., displacement or resistance). The curve helps to visualize how the instrument behaves under varying conditions, such as linear or non-linear responses.

Can you explain the difference between linear and non-linear characteristic curves?

A linear characteristic curve indicates a direct, proportional relationship between the stimulus and the response, meaning the curve is a straight line. In contrast, a non-linear curve indicates a more complex relationship where the response doesn't change in proportion to the stimulus, as seen in the example of a temperature sensor like the PT-100.

What role does sensitivity play in the performance of a measuring instrument?

Sensitivity refers to the ability of a measuring instrument to detect small variations in the stimulus. It is calculated as the ratio of the response to the stimulus applied. The higher the sensitivity, the more accurately the instrument can measure small changes in the stimulus. This property is especially important in instruments used for precise measurements, such as force measuring instruments and temperature sensors.

What is hysteresis, and how does it affect measurement accuracy?

Hysteresis is the difference in the instrument's response when the stimulus is applied in increasing versus decreasing directions. This can lead to measurement errors as the instrument doesn't respond in a consistent way for both directions. It is often caused by mechanical gaps or clearance between components, such as gears or spring elements, which can create inaccuracies.

What is the significance of response time in a measuring instrument?

Response time is the duration it takes for a measuring instrument to react to changes in the stimulus and settle within an acceptable range of accuracy. This is crucial when designing instruments for automation and control systems, as a long response time could lead to delays in measurements and control actions.

How does repeatability differ from reproducibility in measurements?

Repeatability refers to the ability of an instrument to produce consistent results under the same conditions (same operator, same environment). Reproducibility, on the other hand, measures consistency across different conditions, such as varying operators or environmental factors. Both are related to random errors in the measurement system.

What is linearity error, and how is it calculated?

Linearity error is the difference between the actual response of an instrument and its ideal linear response. This error occurs because it is nearly impossible for a measuring instrument to produce a perfectly straight characteristic curve. The error is calculated by comparing the real response to the expected straight-line response over the instrument’s range.

What is the maximum error of an instrument, and how is it represented?

The maximum error of an instrument represents the greatest deviation between the measured value and the true value. It can be graphically represented by plotting the indication of the instrument against the error. The error range includes both systematic and random errors and helps to understand the limits within which the instrument is accurate.

What is the difference between precision and accuracy in measuring instruments?

Precision refers to the consistency of measurements, where repeated measurements yield similar results. Accuracy, however, refers to how close a measurement is to the true or accepted value. An instrument can be precise without being accurate if it consistently deviates from the true value, and vice versa.

Why is it important to express the parameters of an instrument in relative terms?

Expressing the parameters of an instrument in relative terms allows for easier comparison between different instruments, especially those with different ranges or measurement scales. For example, a percentage of full scale or a reference value allows users to compare instruments based on performance relative to their capabilities, helping to make more informed choices.