Signals and Sensors

Flashcards for Signals and Sensors for Mechatronics Design Course

Interference

Unwanted signal that corrupts a signal of interest.

Conductive Coupling

Current flowing through the impedance of shared wires.

Capacitive Coupling

Changing electric fields coupled through parasitic capacitance.

Inductive Coupling

Changing magnetic fields intercepting a measurement loop.

Intrinsic Noise

An unwanted random signal generated within a circuit; mostly caused by thermal vibrations and quantisation of charge.

Random Processes

Modeled using a random process where at each instant, t, the noise is modeled as a random variable.

Power Spectral Density (PSD)

The distribution of noise power with frequency for a stationary random process.

Amplitude Spectral Density (ASD)

The square root of the power spectral density.

Thermal Noise

Noise produced by any resistance.

Semiconductor Noise

Noise produced by semiconductors.

Fourier Transform

Converts a signal into its spectrum.

Fourier Series Analysis

Decomposes a periodic continuous-time waveform into a discrete-frequency spectrum.

Hermitian Spectrum

A quirk of the Fourier transform where the negative frequencies are the complex conju- gate of the positive frequencies, X(−f) = X∗(f) = |X(f)| exp (−j X(f)).

Spectral Density

The spectral density for the units of a spectrum; interpretted as volts per hertz (V/Hz).

Inverse Fourier Transform

The inverse Fourier transform requires X(f) to be known for all frequencies, both positive and negative.

Z-Transform

The z-transform is the discrete equivalent to the Laplace transform and facilitates a turn-the-crank method to solve a difference equation.

Analogue Filters

Unwanted signals attenuate in a signal through analogue filters.

First-Order Low-Pass Filter

The transfer function of a first-order low-pass filter is H(s) = K / (s + α).

First-Order High-Pass Filter

The transfer function of a first-order high-pass filter is H(s) = K s / (s + α).

Second-Order Filters

These filters have a maximum frequency response roll- off of 40 dB/decade.

Integrator

The s-domain transfer function for an integrator is H(s) = 1 / s.

Digital Filters

Digital filters used to reduce noise level, reduce interfering signals, perform differentiation + integration, do Image edge detection, and provide image enhancement.

Discrete-Time Noise Processes

A discrete-time noise signal is a realisation of a discrete-time noise process.

Additive White Gaussian Noise (AWGN)

The most common noise process is additive white Gaussian noise (AWGN).

Two Sample Moving Average Filter

An average formed from two consecutive samples of the input signal, x[n], y[n] = 1 / 2 (x[n] + x[n − 1]).

M Sample Moving Average Filter

An M sample moving average filter can be expressed as y[n] = 1 / M \sum_{m=0}^{M-1} x[n - m].

First-Order Recursive Filter

Defined by the recurrence relation: y[n] = αy[n − 1] + (1 − α)x[n].

Digital Filter Frequency Response

Estimates signal with the frequency response of the filter.

Z-Transform

A z-transformer for filtering that transforms differential equation to algebriac equation.

Discrete Fourier Transform (DFT)

This takes a discrete-time signal, x[n], and computes a discrete- frequency spectrum

Spectrogram

This applies a FFT over a short sequence of N samples to produce a spectrum

Sonar/Radar/Lidar

Method to determine time delay in order to measure range to target.

Pulse Echo Operation

Occurs by sending a modulated pulse of energy and timing when an echo from a target is received.

Triangulation Range Sensing

Estimated range by illuminating target with beam of IR light to measure angle of received beam.

Oscilloscope

Tool used to measure responses in electric circuits.

Sensor Fusion

Weighted measurements combined from different sensors to get lower variance estimate.

Estimator

A function of the observed random process.

Adaptive Filter

Filters automatically adjust, like a control system.

Fourier-Domain

Analyses arbitrary signals with the frequency response.

Frequency Shift

Breaks Hermitian symmetry and creates a complex time signal.