Measurements Quiz 3

What is the difference between Instrument Characteristics and Instrument Specifications?

Characteristics describe the general inherent behavior or performance features of an instrument

Specifications are specific, quantitative details provided by the manufacturer that define expected or guaranteed performance

What are the four primary pairs of instrument types classified in measurement?

1) Active/Passive

2) Null Type/Deflection Type

3) Analog/Digital

4) Indicator/Signal Output

What is the difference between a Passive and an Active instrument?

• Passive Instrument: The output is created entirely by the measured quantity itself.

• Active Instrument: The measured quantity simply controls or adjusts the strength (magnitude) of an external power source

What is the difference between Analog and Digital instruments?

Analog instruments provide measurements using a continuously moving pointer or continuous signal (more durable/cost-effective in harsh environments).

Digital instruments convert physical quantities into discrete numerical values on a screen (higher accuracy, features like data logging/auto-ranging)

What is a Smart Instrument?

An instrument that includes a microprocessor or digital controller capable of signal processing, decision-making, self-calibration, or digital communication

What is Accuracy?

The closeness of a measured value to the true value

What is Inaccuracy (Measurement Uncertainty)?

The difference or bound on measurement error

What is Tolerance?

The permissible limit of error, often set by standards or specifications

What is Precision?

How tightly clustered repeated measurements are to one another

What is the difference between Repeatability and Reproducibility?

Repeatability is measurement closeness under the same conditions (same operator, setup, short time).

Reproducibility is measurement closeness under different conditions (different operators, instruments, times)

What is Linearity?

How close an instrument's actual response is to an ideal straight line

What is Hysteresis?

The difference in output readings at the same input value depending on whether the input is increasing or decreasing

What is Dead Space (or Dead Band)?

The range of input values where no change in output occurs

What is Sensitivity?

The ratio of output change to input change, represented by the slope of the calibration curve

What is Resolution?

The smallest detectable change in input that an instrument can register

What is Threshold?

The minimum input value that produces a detectable output

What is Sensitivity Drift?

A gradual, undesirable change in an instrument's sensitivity over time or due to environmental shifts

What is Sensitivity to Disturbance?

How external variables (such as temperature or vibration) affect the output slope or sensitivity of an instrument

What do the Dynamic Characteristics of a measuring instrument describe?

An instrument's time-dependent behavior between the moment a measured quantity changes and the time the output reaches a steady value (transient state vs. steady state)

zero point calibration

Adjusts the instrument to read zero when there is
no input signal, ensuring an accurate baseline

span calibration

Adjusts the instrument to correctly read a known value at the end of its measurement range, ensuring accuracy across the full scale

linearity calibration

Verifies and corrects any non-linearities in the
instrument's response at various points within its operating range

zero order system

Follows input instantly (e.g., digital caliper)

Approximate, barely exists in the real world

first order system

Includes a time constant (e.g., thermocouple)

Most common type in basic instrument

Second order system

Behaves like a mass-spring-damper system involving natural frequency and damping factor (e.g., accelerometer)

What is vibration?

A mechanical phenomenon whereby oscillations occur about an equilibrium point, which can be deterministic (characterized precisely) or random (analyzed statistically).

What are the main types of vibration?

Free vibration (natural vibration), forced vibration, and damped vibration.

What is a Chladni plate and how does it work?

A flat sheet of metal mounted on a central stalk where sand vibrates away from antinodes and gathers at nodes to form symmetrical patterns when oscillating.

What are Faraday waves?

Nonlinear standing waves that appear on liquids enclosed by a vibrating receptacle, oscillating at half the driving frequency.

Passive vibration isolation

uses materials and mechanical linkages (like springs and dampers) to absorb and damp waves

active vibration isolation

uses sensors and actuators to produce disruptive interference that cancels incoming vibration.

What are mechanical metamaterials?

Rationally designed artificial materials with precision geometrical arrangements whose unusual physical and mechanical properties are derived from their internal structures.

What are some examples of useful vibrations?

Musical instruments, compressors, ultrasonic cleaners, cell phone alerts, and clock pendulums.

What are the primary methods utilizing vibration?

Vibration analysis (machinery health/fault detection)

medical and health monitoring (ultrasound, bone density)

non-destructive testing (NDT, commonly used in construction and manufacturing).

How do piezoelectric-based vibration instruments work?

Mechanical deformation produces an electric charge via the piezoelectric effect (e.g., ICP accelerometers).

How do capacitive and MEMS-based vibration instruments work?

Vibration changes the capacitance between microfabricated plates.

How do laser/optical-based vibration instruments work?

They use optical interference or the Doppler shift to detect motion or velocity (e.g., Laser Doppler Vibrometer).

How do strain gauge-based vibration instruments work?

Vibration causes strain on a surface, leading to a change in electrical resistance.

How do electromagnetic velocity transducers work?

Relative motion between a coil and a magnet induces a voltage proportional to velocity.

What is Time-Domain Analysis in vibration?

An analysis method that examines vibration amplitude and RMS values as they happen second-by-second to see how strong the shake is and spot unusual spikes.

What is Frequency-Domain Analysis using FFT?

A method that uses the Fast Fourier Transform to convert time-domain vibration data into frequency-domain data to identify specific component frequencies.

What is Modal Analysis?

An analysis method that identifies a structure's natural frequencies, mode shapes, and damping characteristics.

What is the Short-Time Fourier Transform (STFT)?

A transform that divides a longer time signal into shorter segments of equal length and computes the Fourier transform separately on each segment to analyze frequency content as it changes over time.

What is the equation of motion for a single-degree-of-freedom Spring Mass Damper (SMD) system?

second order ODE

solution to the SMD system second order ODE

What is the formula for undamped natural frequency

where k is the spring constant, and m is mass

What is the formula for damped natural frequency

where zeta is the damping ratio

What is the formula for the damping coefficient

where zeta is the damping ratio

What is the formula for the critical damping coefficient

where k is the spring constant, and m is mass

What is the damping ratio formula in terms of c and c_c

What is Logarithmic Decrement used for, and what is its formula?

It characterizes the rate of decay in a damped system,

What is number-based data?

Data represented by numerical values involving discrete or continuous measurements (like temperatures, pressures, forces, or voltages) used to quantify measurements directly.

What is figure-based data?

Data represented visually through images, graphs, or plots (such as scatter plots, bar charts, or thermal camera images) used for qualitative interpretation and visualization.

What is signal-based data?

Data represented as a continuous or discrete signal varying over time (such as machine vibration signals or sound waves), shown in either the time domain or frequency domain.

What are the main methods of data cleaning?

Removing outliers from engineering datasets

Handling missing data using techniques like interpolation or removing incomplete records.

What are low-pass, high-pass, and band-pass filters used for?

Data filtering methods used to eliminate noise from sensor signals (such as vibration monitoring data).

What is smoothing in data processing?

Techniques such as moving averages used to reduce signal noise.

What basic statistics are commonly used in statistical processing?

Mean, variance, standard deviation, and Root Mean Square (RMS).

What correlation methods are commonly used in statistical processing?

Autocorrelation is used to detect periodicity within a signal

Cross-correlation measures the similarity between two different signals.

What are normalization and standardization used for in data transformation?

Adjusting data to comparable scales.

What is the purpose of a Fourier Transform in data processing?

Converting time-domain data into the frequency-domain to analyze signal frequency content.

What is the purpose of a 2D Fast Fourier Transform (FFT)?

It can determine the spatial frequency of an image.

What does the fftshift function do in MATLAB?

It performs a zero-centered, circular shift on a discrete Fourier transform to better visualize its periodic nature across positive and negative frequencies.

What are the three damping regimes in a spring-mass-damper system based on the damping ratio?

Underdamped (oscillatory decay)

Critically Damped (fastest return to equilibrium without oscillation)

Overdamped (slow, non-oscillatory return to equilibrium).

What is Logarithmic Decrement used for?

It is used to characterize the rate of decay in a damped vibration system.

deflection type instruments

• measure a quantity by creating a mechanical deflection, usually of a pointer against a scale

• Accuracy depends on the linearity and calibration of spring

• Usually more convenient and has faster response.

null-type instruments

• measuring by balancing the measured quantity against a calibrated standard until a null or zero deflection is achieved

• Accuracy depends on the calibration of weights (easier)

• Usually more accurate