instrumentation exam 1

transducer

a device that translates energy from one form to another (ex: light bulb, motor)

biotransducer

a device that converts energy from a physiological process into a voltage (or current) with an amplitude proportional to the input energy

biotransducers establish the _____ or ______ of a particular system

risk or invasivness

encoding

process of representing information in the form of a signal(s) (ex: human speech vs morse code)

continuous signal

signal encoded via amplitude (intensity)

discrete signal

signal transmitted as pulses at specific intervals, encoded via pulse length

(stair steps)

analog

continuous signal that is encoded linearly

ex: temp=2*voltage amplitude

digital

analog signals represented by a series of discrete samples

analog signals must be _______ in both time and amplitude to digitize

sliced

time slicing

discretization

amplitude slicing

quantization

quantization

the process of changing a continuous set of values to a discrete set, usually refers to binning signal magnitude

discretization

the process to transform a continuous time signal to discrete time process

nyquist frequency

=2*highest frequency of signal

maximum signal

=2ⁿ-1

resolution of the ADC / system voltage =

ADC reading / analog voltage measured

two major types of systems concerning bioinstruments

linear vs nonlinear

linear systems

feature a proportional relationship between input and output y=f(x)

nonlinear systems

do not hold to a proportional relationship

electric charge (Q)

physical property of matter, positive or negative, units coulombs [C]

Current (I)

flow of charge, measured through an element with respect to time, units of Amperes [A]

Voltage (V)

potential energy per charge, measured across an element, units volts [V]

resistivity (ρ)

a material dependent constant

R=

ρ*l/A

resistors in parallel

R1*R2/R1+R2

resistors in series

R1+R2

kirchoffs voltage law

sum of voltages around a loop is equal to 0

kitchoffs current law

sum of currents at any node is equal to 0

resistive sensors

use the fact that an element can have a resistance change due to an external stimulus

wheatstone bridge circuit

two voltage dividers in parallel, used to measure resistances of unknowns

a wheatstone bridge circuit is balanced when

Ra/Rx=R1/R2

strain gauge

resistor based sensor, resistance changes with strain, use a bridge circuit to measure resistance

measuring temperature

thermocouple, thermistor

voltage division formula

V0=Vin *(R2/R1+R2)

wheatstone bridge circuit formula

V_1,2=Vin(Rx/Rv+Rx - R2/R1+R2)

linear system

feature a proportional relationship between input and output

nonlinear system

do not hold a proportional relationship

capacitor

stores energy

-CV=Q → I=C(dV/dT)

capacitors are useful in

local energy storage, voltage spike supression, signal filtering, resist sudden changes in voltage

parallel plate capacitors are composed of

conductive plates, insulating dielectric, nonconductive material

charging capacitor

fully charged capacitor

inductor

results from magnetic fields around the conductor

-V=L(dI/dT)

inductors are used for

control spikes in current, create oscillators, proximity sensing applications

analog circuit relationships

Z=R+jX where Z is total impedence, R is resistance, X is capacitance/ inductance

network reduction is a process of ________ the number of elements in a complex circuit to simplify its analysis

reducing

-90 degree

fully charged reactance

+90 degrees

fully inductance

inductor XL=

jωL

capacitor Xc=

1/jωC

resistor and inductor in series ZL=

RL+jωL

resistor and capacitor in series Zc=

Rc-j/ωC

voltage current method

applies a known voltage across two nodes of interest and measures the current

Zeq= Vknown/Imeasured

used when circuit is unknown

RC circuit

1st order linear differential equation with constant coefficient

t=0 capacitors

capacitor acts as a short circuit, current flowing but enough time has not passed

t→ ∞ capacitor

acts as an open circuit, charge is now saturated, so current effectively becomes 0

discharging

decreasing voltage, negative spike in current

charging

increasing voltage, spike in current then decreases

t=0 inductors

acts as an open circuit, no current flowing

t→∞ inductor

acts as a short circuit, current flows freely through the element because field is maximized

RLC circuit

a 2nd order differential equation with constant coefficient

laplace transform

in cases where signals change suddenly

examples of when to use laplace transforms

stepwise, transient

sinusoidal signals

offer unique properties for many useful signal analysis

many complex signals can be broken down into…

sinusoids or a series of sinusoids (fourier), signals must be periodic

sinusoids have energy at…

only one frequency (pure tones)

a sinusoidal input into a linear system will…

yield a similar sinusoidal output (same frequency and shape, different magnitude and phase)

given that two sinusoids are harmonically related…

they are orthogonal to each other, this means that they can be independently decomposed without interference

when can fourier analysis be used

in cases where signal is not changing in stepwise (transient) fashion

Fourier transforms

used to shift from the time domain to the frequency domain

transfer functions

describes the behavior in the frequency or s- domain

H(s)=

H(jω)=Vout/Vin

low pass filter

nonlinear circuit elements _______ use superposition

cannot

diode

only lets current go one way

LED

light emitting diode

photodiode

used for measuring light

rectfier circuit

half recitifier

negative component becomes 0

full wave rectifier

negative component becomes positive

transistor

semiconductor devices used to amplify or switch electronic signals

Bipolar Junction Transistor (BJT)

composed of two diodes, sandwhich an n-type or p-type semiconductor material generating 2 n-p junctions

three terminals of BJTs

base, emitter, collector

BJTs are useful in amplifiers due to…

controllable by small base current, low input impedence device

two types of Field-Effect Transistor (FETs)

junction FET (JFET), metal-oxide FET (MOSFET)

JFETs feature a

p-n junction

MOSFETs feature a

insulating material

three terminals of FETs

drain, source, gate

both types of FETs have

a high input impedence, control a drain-source current via an applies gate-source voltage

FETs are useful…

in amplifiers (most of market share in commercial devices) and in power switching applications

op amp

critical for amplification or active filtering, powered element, two inputs, 1 output, 2 DC power inputs

2 inputs for an op amp

inverting and noninverting

2 DC power inputs op amps

positive and negative power supply (ceiling and floor)

basic op amp

amplifies difference in inputs

OP Amp saturation

comparator

use the fact that omp amps saturate very easily

ideal op amp

infinite gain and no offset voltage, infinite input impedence, zero output impedence, no noise, infinite bandwidth, no change with temperature

noninverting amplifier

gain= (noninverting)

why use op amps

two inputs are isolated from each other