NMJ30403 Instrumentation - Measurement

Comprehensive vocabulary flashcards covering the key definitions, measurement parameters, error types, statistical analysis formulas, and instrument classifications from the NMJ30403 Instrumentation lecture.

Instrumentation

The branch of engineering defined as the art and science of measurement and control, serving sciences, engineering, medicine, and almost every human endeavor.

Electronic Instrumentation

The application of measurement technology in electronic-related fields, where knowledge of performance characteristics is essential for selecting suitable measuring instruments.

Measurement

The process of comparing an unknown quantity with an accepted standard quantity, or determining the amount, degree, or capacity by comparison with accepted system unit standards.

Displacement

A vector representing a change in position of a body or a point with respect to a reference.

Strain

The relative deformation of elastic, plastic, and fluid materials under an applied force.

Vibration

Oscillatory motion described in terms of amplitude (size), frequency (rate of oscillation), and phase (timing of the oscillation relative to a fixed time).

Pressure

The ratio of force commonly acting on a surface to the area of the surface.

Flow

A stream of molten or liquefied material that can be measured in terms of speed and quantity.

Temperature

The measure of relative warmth or coolness of an object compared to an absolute value.

Force

A quantity that changes the motion, size, or shape of a body.

Torque

The tendency of a force to rotate the body to which it is applied.

Primary Sensor

An instrument element that produces an output as a function of the measurand (the input applied to it), such as a thermocouple or a strain gauge.

Variable Conversion Element

An element needed when the output variable of a primary transducer is in an inconvenient form and must be converted to a more convenient form.

Transducer

A measurement device formed by the combination of a primary sensor and a variable conversion element.

Signal Processing Element

An element that improves the quality of the output in a measurement system, such as an electronic amplifier.

Transmitter

A device formed when signal processing is incorporated directly into a transducer.

Signal Transmission Element

An element required when the observation or application point is distant from the primary transducer, traditionally using single or multicored cable to minimize electrical noise corruption.

Signal Presentation Element

The final optional element in a measurement system where the measured signal is utilized, recorded, or displayed.

Static Characteristics

Instrument performance characteristics obtained by calibration when measuring a constant process condition, including accuracy, precision, resolution, and sensitivity.

Dynamic Characteristics

Instrument performance characteristics observed when measuring a varying process condition, including speed of response, fidelity, lag, and dynamic error.

Absolute Error

The numerical difference between the expected value and the measured value, expressed as $e = Y_n - X_n$, where $Y_n$ is the expected value and $X_n$ is the measured value.

Percentage Error

The ratio of absolute error to expected value expressed as a percentage: $\% \text{ error} = \left(\frac{Y_n - X_n}{Y_n}\right) \times 100\%$.

Relative Accuracy

A quantitative measure of closeness to the true value, given by $A = 1 - \left|\frac{Y_n - X_n}{Y_n}\right|$, where $Y_n$ is the expected value and $X_n$ is the measured value.

Precision

A numerical indication of the closeness with which repeated measurements of the same variable agree with their average, expressed as $P = 1 - \left|\frac{X_n - \bar{X}_n}{\bar{X}_n}\right|$.

Static Error

The numerical difference between the true value of a quantity and its value as obtained by measurement when repeated measurements yield different indications.

Gross Errors

Errors caused by human mistakes in reading or using instruments, incorrect adjustment, and computational mistakes, which are minimized by careful observation and taking at least three readings.

Systematic Errors

Errors resulting from shortcomings of the instrument, such as worn parts, calibration defects, or environmental effects, subdivided into static and dynamic errors.

Instrumental Errors

Systematic errors inherent in measuring instruments due to mechanical structure, such as bearing friction, irregular spring tension, or spring stretching.

Environmental Errors

Systematic errors caused by external conditions such as changes in temperature, humidity, barometric pressure, or electrostatic and magnetic fields.

Observational Errors

Systematic errors introduced by the observer's habits, most commonly parallax error and scale estimation errors.

Random Errors

Errors due to unknown causes remaining after gross and systematic errors have been accounted for, minimized by increasing the number of readings and using statistical analysis.

Arithmetic Mean

The most probable value of a measured variable obtained from a set of readings, expressed as $\bar{x} = \frac{\sum_{n=1}^n x_n}{n}$.

Deviation from the Mean

The departure of a given measurement reading from the arithmetic mean of the group of readings, expressed as $d_n = x_n - \bar{x}$.

Average Deviation

An indication of instrument precision defined as the sum of the absolute values of all deviations divided by the total number of readings: $D_{\text{av}} = \frac{\sum |d_n|}{n}$.

Standard Deviation

Also known as root mean square deviation, the most important factor in the statistical analysis of measurement data: $\sigma = \sqrt{\frac{\sum d_n^2}{n}}$.

Limiting Error

The guaranteed accuracy tolerance specified by a manufacturer as a percentage of full-scale reading, which increases in percentage as readings decrease below full scale.

Absolute Instrument

An instrument providing the magnitude of a quantity directly in terms of physical constants without requiring calibration or comparison against other instruments.

Secondary Instrument

An instrument that determines the magnitude of a measured quantity from observed output, requiring calibration against an absolute instrument or another calibrated secondary instrument.

Deflection Type Instrument

An instrument requiring only one source of input where the measured reading depends on calibration and deflection from its initial state.

Null Type Instrument

An instrument requiring two inputs (measurand and balance input) that uses feedback to compare the measurand against a standard, offering higher accuracy and sensitivity than deflection types.

Analog Instrument

An instrument producing an output signal that varies in a continuous manner across an infinite range of values in any given range.

Digital Instrument

An instrument producing an output signal that varies in discrete steps across finite values in a given range.