Calibration Methods and Processes

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Questions and Answers

What is the definition of calibration?

Calibration is the process of applying a known value to the input of a measuring system to observe its output and establish the relationship between the input (independent variable) and output (dependent variable) of the system.

What are the three things that calibration involves comparing a calibrated instrument/equipment with?

  • a tertiary standard with the lowest accuracy
  • a known input source (correct)
  • a primary standard (correct)
  • a secondary standard with higher accuracy (correct)

What does sensitivity refer to in a measuring system?

Sensitivity refers to the slope of the graph obtained from a static calibration and represents the relationship between a change in the indicated output associated with a change in the static input. It also refers to the smallest change in measurement that the measuring system can detect.

What is the formula for range in a measuring system?

<p>r₁ = Xmax - Xmin</p> Signup and view all the answers

What is the formula for calculating the absolute error in a calibration?

<p>abs. error, e = true value - indicated value</p> Signup and view all the answers

What is the formula for calculating the percent relative accuracy during calibration?

<p>A = 1 - (e/true value) x 100</p> Signup and view all the answers

A measuring system can be precise but not necessarily accurate.

<p>True (A)</p> Signup and view all the answers

What is the formula for calculating the hysteresis error?

<p>e_h = Y_upscale - Y_downscale</p> Signup and view all the answers

What does random calibration aim to achieve?

<p>Random calibration aims to break up hysteresis and observation errors by applying random sequences of known input values within the calibration range, providing a more realistic simulation of actual measuring situations.</p> Signup and view all the answers

What is the general form of linear static calibration?

<p>y_L (x) = a_0 + a_1x</p> Signup and view all the answers

How is the linearity error calculated?

<p>linearity error, e₁ (x) = y (x) - y_L (x)</p> Signup and view all the answers

What is the formula for calculating the percentage of linearity error in terms of FSO?

<p>%e₁ = (e_Lmax / r_0) x 100</p> Signup and view all the answers

What is sensitivity error in a calibration?

<p>Sensitivity error, e_k, is a statistical measure of the precision error in the estimate of the slope of the calibration curve, which arises from scatter in the measured data during calibration.</p> Signup and view all the answers

What does zero error represent in a calibration?

<p>Zero error, e₂, represents the shift of the zero intercept of the calibration curve. It indicates the offset or bias in the measurement output when the actual input is zero.</p> Signup and view all the answers

What is repeatability in a measuring system?

<p>Repeatability refers to the ability of a measuring system to indicate the same value upon repeated but independent applications of the same input.</p> Signup and view all the answers

What statistical measure is repeatability based on?

<p>Repeatability is based on the statistical measure of standard deviation (S_x), which measures the variation in the output for a given input.</p> Signup and view all the answers

Repeatability reflects all types of errors during the actual measuring process.

<p>False (B)</p> Signup and view all the answers

What is the formula for calculating the percentage of repeatability error?

<p>%e₁ = (2S_x / r_0) x 100</p> Signup and view all the answers

What is a standard in terms of calibration?

<p>A standard is a reference value used for calibration. It can be a well-trusted equipment, an object with well-defined physical properties, or a well-accepted technique that produces reliable values.</p> Signup and view all the answers

Standards can only be equipment with well-defined physical properties.

<p>False (B)</p> Signup and view all the answers

What are the three main types of standards?

<p>The three main types of standards are primary standards, secondary standards, and working standards. Primary standards are the most accurate and serve as the ultimate reference. Secondary standards are less accurate but are more practical for daily use. Working standards are used for routine calibration and are calibrated against secondary standards.</p> Signup and view all the answers

What is the difference between a dimension and a unit?

<p>A dimension is a physical variable used to specify the behaviour or nature of a system or object. It refers to the concept or quantity being measured. A unit is a specific term used to measure the dimension. It provides a standard scale for expressing the value of the dimension.</p> Signup and view all the answers

What is the significance of defining units by primary standards?

<p>Defining units by primary standards ensures that they are exact and accurate. By using internationally agreed-upon primary standards, we ensure consistency and avoid confusion in scientific and technical measurements.</p> Signup and view all the answers

What are the key considerations for selecting a primary standard?

<p>Key considerations for selecting a primary standard include its universal availability, continuous reliability, stability, and minimum sensitivity to surrounding elements. It should be readily accessible, maintain its accuracy over time, resist changes in environmental conditions, and be minimally affected by external influences.</p> Signup and view all the answers

The International Measuring System (SI) provides standards for all physical dimensions.

<p>False (B)</p> Signup and view all the answers

What is the standard mass defined as in the SI unit?

<p>In the SI unit, the standard mass is defined as one kilogram, which is represented by the mass of a platinum-iridium bar kept at the International Bureau of Weights and Measures in France.</p> Signup and view all the answers

What is the definition of the standard length in the SI unit?

<p>The standard length in the SI unit is defined as one meter, which is equivalent to the distance traveled by light in a vacuum in 1/299,792,458 of a second.</p> Signup and view all the answers

What is a primary standard in the context of calibration?

<p>A primary standard is the ultimate reference for calibration, representing the most accurate and precise value for a specific dimension.</p> Signup and view all the answers

What is a secondary standard in the context of calibration?

<p>A secondary standard is a duplicate or close approximation of the primary standard. It is used for calibration when the primary standard is impractical.</p> Signup and view all the answers

The hierarchy of standards means that the lower the standard, the lower the chance of uncertainty and errors.

<p>False (B)</p> Signup and view all the answers

What is the purpose of standard operating procedures (SOP's)?

<p>Standard operating procedures (SOPs) aim to ensure a consistent and proper way of conducting experiments or measurements, reducing the variability of results arising from different individuals or methods.</p> Signup and view all the answers

What is the role of SIRIM in Malaysia?

<p>SIRIM, the Standards and Industrial Research Institute of Malaysia, is responsible for maintaining secondary standards at the national level, ensuring the accuracy and reliability of calibration practices within the country.</p> Signup and view all the answers

Flashcards

Calibration

Comparing a measuring system's output to a known input value to understand the system's accuracy.

Static Calibration

Calibration where the input values remain constant over time.

Dynamic Calibration

Calibration where input values change over time. Measures how the system responds to changing inputs.

Sensitivity

A measure of how much the output changes for a given change in the input.

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Range

The difference between the maximum and minimum values a measuring system can accurately measure.

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Accuracy

How close a measurement is to the true value.

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Precision

How repeatable a measurement is.

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Sequence Calibration

Calibration method where input values are progressively changed.

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Primary Standard

A highly accurate and well-defined reference for calibration.

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Secondary Standard

A standard with good accuracy used to calibrate other instruments.

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Absolute Error

Difference between the measured value and the true value.

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Percent Relative Accuracy

Percentage of accuracy indicating how close the measurement is to the true value.

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Input Range

Span of input values measurable by the measuring system.

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Output Range

Span of output values produced by the measuring system.

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Study Notes

Calibration Overview

  • Calibration is a method of comparing a measuring system to a known standard.
  • This is done by applying a known value to the input of the system and observing the output.
  • The relationship between the input and output values is established.

Calibration Process Example

  • A known mass (e.g., 1 kg, 2 kg) is placed on a weighing scale.
  • The weighing scale provides an output value (e.g., 1 kg, 2 kg).
  • Comparison of actual and expected values shows if the scale is calibrated correctly.

Types of Calibration

  • Static Calibration: The measured variable(s) remain constant over time. Only input magnitude and output are important.
  • Dynamic Calibration: The measured variable(s) change over time. The relationship between the input (that changes) and the output is determined.

Sensitivity

  • Sensitivity is the slope of the graph from a static calibration.
  • At a specific input (x₁), sensitivity (K) is calculated as K = Kx₁ = (dy/dx)x=x₁.
  • It's the relationship between output change and input change.
  • It represents the smallest detectable change in measurement.

Range

  • Range is the difference between the maximum and minimum values.
  • Proper calibration should cover the entire range of intended use.
  • The operating range (rᵢ) is defined by the maximum (Xmax) and minimum (Xmin) input values.
  • Avoid measurement outside the calibration range.

Accuracy

  • Accuracy measures how closely a measurement reflects the true value.
  • The true value is the known input during calibration.
  • Absolute error (e) is the difference between the true value and the indicated value.
    • e = true value - indicated value
  • Percent relative accuracy (A) is calculated as A = 1 - (e/true value) * 100.

Precision

  • Precision (repeatability) is the ability of a system to provide the same value upon repeated measurements of the same input.
  • A precise system can have low accuracy.

Sequence Calibration

  • Sequential variation of the input is applied over the desired range, either upscale (increasing input) or downscale (decreasing input).
  • This is used to identify and quantify hysteresis.
  • Hysteresis error (eh) is the difference between upscale and downscale calibration values.
    • eh = Yupscale - Ydownscale

Hysteresis

  • Hysteresis arises when the output depends on the previous indicated value.
  • It's often expressed as a percentage of full-scale output (FSO).
    • %eh = (eh max / ro) * 100

Random Calibration

  • Random input values are used over the intended range.
  • This helps break up hysteresis and observation errors, more closely simulating actual measurements.
  • It aids in quantifying characteristics like linearity error, sensitivity error, zero error, and repeatability error from static random calibration.

Linearity Error

  • Many measurement systems aim for a linear relationship between input (x) and output (y).
  • The general equation for linear calibration is Y₁ = a₀ + a₁x.
  • The curve y₁(x) provides a predicted output based on the linear relationship.
  • Linearity error is the difference between the actual output and the predicted linear output.
    • e₁ = y(x) - y₁(x)
  • Linearity error is expressed as a percentage of FSO.

Sensitivity Error

  • Scatter in calibration data impacts precision.
  • Sensitivity error (ek) is a statistical measure of the slope of the calibration curve's precision error.

Zero Error

  • Zero error (ez) is the shift of the zero intercept of the calibration curve.
  • The offset from zero input to a non-zero output value. It's not always a constant.

Repeatability

  • Repeatability is the ability of a system to give the same value with repeated applications of the same input.
  • The variation in output for a given input, usually expressed as a percentage of FSO.
    • %er = (2Sx / ro) * 100

Standards

  • Calibration involves comparison with standards with known values.
  • These standards can include equipment trusted by users, objects with precise properties, or well-established techniques.

Units versus Dimensions

  • Dimensions describe physical attributes like length, mass, and time.
  • Units are used to measure dimensions (e.g., meters for length, kilograms for mass).
  • Standardized units, like those of the International System of Units (SI), avoid confusion and ensure accuracy.
  • Primary standards, often impractical, are the ultimate reference.
  • Secondary standards are less precise copies for more practical use.

Hierarchy of Standards

  • A hierarchy of standards exists, ranging from primary (most accurate) to local (least accurate).
  • Moving down the hierarchy increases the chance of errors.
  • Standard operating procedures (SOPs) often accompany standards to create consistency and ensure reliable experiments.
  • In Malaysia, SIRIM manages and maintains standards at a national level.

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