28-34;Magnets/Thermocouples/Pressure Transducers/Evaluation of VA Characteristic of crystal diode Flashcards
simple magnets
have 2 poles N/S
if N of 2 magnets brought together = repels, N+S attract
arrows along field lines = direction of magnetic field, density of lines = relative strength of magnetic fields
field strongest at pole, directed outwards from N
EG magnetic compass, needle is small magnet = rotates to align N pole/direction of earth’s magnetic field = used to map
diamagnetic
when substances of small -ive magnetic character lines up at right angles to non-uniform magnetic field = exhibits paramagnetism
ferromagnetism
result of long-range ordering of atoms of solids into domains = small ordered region = the domains act like a tiny magnet
EG Iron, Nickel
what happens when u heat up magnet
destroys magnetic ordering = won’t show ferromagnetic property
electromagnet
electric current flowing though straight wire to generate magnetic field
if long current-carrying wire bent into loop = magnetic fields add together inside loop = stronger magnetic field = solenoid
X - large current required for useful magnetic field
how are practical electromagnetics made
adding iron core to solenoid = small magnetic field causes domains of iron’s ferromagnetic core to line up = produces additional magnetic field
interaction btw electricity and magnetism
electricity and magnetism are manifestations of the same basic force = electromagnetic force
does magnetic field exert force on charge
magnetic field exerts no force on a charge at rest or charge moving parallel to magnetic field
if MF small = charge passes through = deflects charge from OG path
if MG large enough to trap charge = charge moves in circular path = MF provides centripetal force necessary to move charge in circle
electric motor principle
current-carrying wire in MF experiences force perpendicular to wire
electric motor
collection of wire loops arranged on rotor suspended in MF and spins freely
when electric current flows through loops, force produced perpendicular to each section or wire
MF up on 1 side of coil, down on other = produces torque to rotate motor = moving coil meter
magnetic flux
measure of no. of magnetic field lines that cross a given area
faraday’s law
describes induction by relating EMF induced in circuit to rate of change of magnetic flux through circuit
-ive sign = induced magnetic field opposes the change that created it
EG Ultrasound scan, NMR imaging, doppler pulse
sensing elements for physiological measurements/transducers
no. of physiological measurements made using sensors that covert physiological data to small electrical signals.
electrical image can be easily transmitted to remote monitoring point, amplified and displayed to be measured
thermocouples
temp sensor consisting of junction between 2 different metals
2 tiny wires spot-welded together at sensing junction, ref junction connected to measuring device to measure thermal electromotive force/thermo emf
temp-voltage transducer = V depends on metal wire and Temp
electrical resistance thermometer
thermal agitation of atoms of metal increases w/ temp = resistance to electric current flow increases
temp sensors of platinum wire
most accurate, cannot be miniaturised
thermistor
similar to electrical resistance thermometer, electric resistance changes w/ temp = as R increases T decreases
can be miniaturised, more sensitive, easily calibrated, doesn’t have extreme accuracy
pressure transducer
produces electrical signal proportional to pressure exerted upon it
EG. microphones=form electrical image of P variation in air caused by sound
oximeter
EG of sensing element using light to determine O2 content of blood
small sample of blood illuminated w/ red light, reflected light from blood enters photoelectric cell = amount of light reflected determine % of O2 saturation of Hb
electrodes for pH/CO2/O2
pH electrode = small glass bulb selectively permeable to H+, inside bulb is silver electrode coated w/ AgCl and immersed in buffer sol of pH1 = when electrode placed in liquid of unknown pH = diffusion process = small V on electrode = determines pH
amplifiers
produce distortion free replica of OG signal
require large amount of electrical power to display physiological data
display devices
numerical values in physiological data taken from display device
EG. oscilloscope
transistor
found in amplifiers which use = miniaturized solid-state integrated circuits w/ many transistors
oscilloscope
cathode ray oscilloscope display for monitoring physiological data
visual display of V varies w/ time
cardiac monitor = repetition rate + detailed shape of ECG V pattern +several physiological variables (SP/DP) observed
meters and chart recorders
moving coil meter = current-carrying wire experiences force when placed in magnetic field = exerts force both sides = torque = proportional to current through coil = indicating needle attached to coil, its position calibrated in terms of coil
adopted to measure V or R
large resistor in series w/ coil = Voltmeter = I flowing thru coil proportional to V across combination
Ohmeter= battery ok known V in series w/ coil
x slow response
digital display
LED/LCD = small and dependable = electrical signal converted to digital form = used for other functions
defibrillator
high V device, large capacitor for emergency resuscitation from heart stoppage or ventricular fibrillation
momentary large I flows through heart - stops fibrillation and normal heart rhythm resumes
electrosurgery/cautery
electrosurgical instruments used for cutting/welding tissue together
high I density/V freq causes cutting/cauterizing action
