BEEE 152 Measurement and Instrumentation - Unit I Fundamentals

A set of vocabulary flashcards based on Unit I: Measurement Fundamentals, covering key terms, system elements, static and dynamic characteristics, error classification, and measurement standards.

Measurand

The physical quantity being measured, such as temperature, voltage, or force.

Instrument

The device used to determine the value of the measurand.

Sensor

The part of the instrument that responds directly to the measurand.

Calibration

The process of adjusting an instrument so its readings agree with a reference standard.

Standardisation

The act of establishing accepted reference values and procedures for measurements.

True value or expected value

The value that a perfect measurement would give, which is never exactly known.

Measured value

The actual value obtained from an instrument or recorded during observation.

Reading

The numerical value that the instrument displays to the user.

Primary sensing element

The functional element that makes first contact with the measurand, such as a thermocouple junction or pressure diaphragm.

Variable conversion element

The element that changes the sensed quantity into a usable form, such as converting emf to voltage.

Variable manipulation element

The component of a measurement system that amplifies, filters, or scales the signal.

Data transmission element

The element that carries the measurement signal to the display via media such as wire, fibre, or radio.

Data presentation element

The component that shows the final result to the user, such as a pointer, digital display, or computer screen.

Direct method

A measurement method where the measurand is compared directly with a standard, such as weighing rice on a balance against standard masses.

Indirect method

A measurement method where the measurand is computed from other measured quantities using a known formula, like calculating power as $P = V \times I$.

Static characteristics

The set of criteria that describe how an instrument behaves when the measurand is not changing in time, measured under steady-state conditions.

Accuracy

The closeness of a reading to the true value, usually expressed as a percentage of the full-scale deflection (FSD).

Precision

The closeness of repeated readings of the same quantity to each other.

Resolution

The smallest change in input that produces a detectable change in the output, such as the last digit on a digital voltmeter.

Sensitivity

The ratio of the change in output to the change in input ($S = \frac{\triangle(\text{output})}{\triangle(\text{input})}$), or the input resistance per volt of full scale ($S = 1/I_{fsd}$) in \text{\Omega/V}.

Linearity

How closely the calibration curve of an instrument matches a straight line, expressed as the maximum deviation from a best-fit line as a percentage of FSD.

Hysteresis

A characteristic where an instrument gives different readings for the same input depending on whether the input was approached from a lower or higher value.

Dead zone

The range of input over which no output appears at all, often caused by static friction.

Drift

A slow change in output over time while the input remains constant, due to factors like component ageing or temperature changes.

Reproducibility

The closeness of readings taken at different times under similar conditions.

Dynamic characteristics

The criteria describing how an instrument behaves when the measurand is changing with time.

Speed of response

A dynamic characteristic measuring how quickly the output of an instrument follows a change in input.

Fidelity

The degree to which an instrument faithfully reproduces the shape of the input signal.

Dynamic error

The difference between the true value and the indicated value during a rapid change in the measurand.

Bandwidth

The range of input frequencies for which the instrument response remains within an acceptable error band.

Absolute error ($\epsilon_a$)

The difference between the measured value ($A_m$) and the true value ($A_0$), calculated as $\epsilon_a = A_m - A_0$.

Relative error ($\epsilon_r$)

The ratio of the absolute error to the true value, expressed as $\epsilon_r = \frac{\epsilon_a}{A_0}$.

Gross errors

Errors caused by human mistakes like misreading, miscalculation, or wrong setup that cannot be analyzed statistically.

Systematic errors

Reproducible biases from instruments, environment, or methods that occur the same way every time a measurement is repeated.

Random errors

Unpredictable scatters from many small unknown causes that can be reduced by averaging multiple readings.

Limiting (Guarantee) Error

The maximum possible error of an instrument specified by the manufacturer, typically as a percentage of full-scale value.

Traceability

The unbroken chain of calibrations linking a working instrument back to the SI definition through international and national standards.