Download Chapter 9 (Part B)

Chapter 9. Principles of Electricity for Electrotherapy (Part B)
Electrical Generation/Conversion
•Process of converting another form of energy into ________________ energy
•Most electricity is converted from thermal, chemical, mechanical, or solar energy.
•Look at only two:
–Chemical:
Zn
–Mechanical:
Cu
H2 SO4 H2 SO4
Chemical Generation of Electricity
H2 SO4
H2 SO4
•Most common form =
•Two different __________ plates are put into a solution
•____________ are liberated from 1 plate and _________ on the other plate
•If a __________ is attached to the 2 plates, ____________ will flow from the plate with
____________ electrons, through the ____________, to the plate that lost
______________ (deficit)
2−
•SO4 attracts Zn2+ from the zinc plate, leaving it _______________ charged.
•SO42− and Zn2+ combine to form ZnSO4, which then precipitates to the bottom of the
battery.
Zn -
Cu
SO--
4 H SO
Zn++H SO
2
4
4
2
ZnSO 4 2H+ + SO-- 4
•H+ ions pull an ____________ from a copper molecule and becomes free ____________. (#2)
•The copper plate becomes ___________________ charged (Cu2+).
Zn -
+ Cu
o
o o o
o
2H
H2 SO4
H2 SO 4
ZnSO 4 2H + SO-- 4
+
•As the process continues, charges accumulate and a difference in potential (voltage) develops
between the negatively charged Zn2− plate and the positively charged Cu2+ plate.
•If a wire is attached between the two plates, electrons flow from the plate with the extra
electrons to the plate that lost electrons.
–Which way do electrons flow?
–Which way does current flow?
•Remember: Although electrons flow from the Zn− pole to the Cu+ pole, we say that current
flows from the Cu+ pole to the Zn− pole.
•Because electrons always flow from one pole to the other, it is called direct current.
1
Types of Batteries
• (1) Galvanic or wet cells
•A wet cell consists of two __________ and an _____________________ solution
(earlier example)
–Example:
•(2) Dry cell
–Electropaste rather than solution
–Zinc-carbon battery
•Zinc tube filled with __________________ and a carbon rod inserted into the
middle
–Example:
•Storage batteries
–
–An electric current passes through it, causing a reverse chemical reaction.
•Restores the H2SO4
–Reaction can go again.
Mechanical Power: Generation/Conversion
•Based on the relationship between _________________
and ___________________
•Magnetic field
–Force that develops when a critical number of a
substance's ________________ molecules
________________
–The substance is said to have
____________________
–A ________________ field develops between the
two ________________ and is called a
_______________ field.
Generating AC Current, Simplified
Electromagnetic induction
•When _________________ passes through a wire, a ________________ field is
created.
•Conversely, when a coil of ________________ wire is moved toward or away from a
____________________, electricity flows in the wire.
•An electrical generator consists of:
–A bar _________________ mounted on a rotating pedestal
–Two ____________ plates positioned at the end of the magnet and connected
with a large loop of wire (or a metal core with a coil of wire around)
–Source of ______________________ energy to keep the bar magnet spinning in
a circle.
–Common mechanical forces:
2
•Magnet in starting position
–Its ___________ pole attracts _____________
–Its ___________ pole repels _____________
•Electrons flow through the core, inducing electron flow
in the wire coil,
•Rotate the magnet 180°.
•The poles are now reversed, so electrons move in the opposite direction.
•Continue rotating, and AC flows through wire coil.
•As long as there is __________________ power keeps the magnet turning, _____ current will
flow
Electrical Motor vs. Electrical Generator
•Electric motor: conceptually the same as but ________________________ of generator
–Consist of the same basic components, except the processes are opposite
•Generator converts ______________________ energy to __________________ energy
•Electrical motor converts __________________ energy to _________________ energy
AC Terms
 Impulse
•Current flow in a _______________ direction
•Appears as a half ___________
•Portion of graph representing current flowing from
_________________ to ____________________ in
_____ direction and back to the ______________
•When generating AC current, represents electron flow
during time magnet rotates __________
3
•Cycle
–Two
impulses
•Portion of graph representing current flow from _________________ to
__________________ in ___ direction, back across _________________ to
__________________ in _________________ direction, and back to
______________________
•Electron flow as magnet rotates __________
•Frequency
–Cycles/sec (cps): the number of _________________ completed each ____________
–Low-frequency current: <1000 cps
–High-frequency current: >1,000,000 cps
Devices for Measuring and Regulating Electricity
•Based on electromagnetic effects of current
–Permanent _______________ and
________________________ that can rotate
–When charged, ______________ repel each other, causing
the ________________________ to rotate away.
–Repulsion is proportional to the strength of the
electromagnet (proportional to the amount of
________________).
•Ampmeter (ampere meter)
–Measures ______________ of flow of current
•Voltmeter
–Measures ___________________
•Ohmmeter
–Measures ___________________ to current flow
4
Output Current Characteristics
•Input current (AC or DC) is manipulated, regulated, and adjusted to create different output
current forms.
•Sends (outputs) to tissue:
–
–
–Continuous flow of electrons in a _______________ direction
–
–
–Continuous back-and-forth flow of ____________________
–Defined by ____________________ or cycles per __________________
–Can be turned off and on to create bursts
–
–
–
– _____________________ electron flow
–The simplest form of interruption is to turn
the switch _____ and __________
Current Modulation
•Includes all manipulating, regulating, and adjusting to create a variety of specific output wave
forms
•Most output pulsed or as ____________ trains
•Factors modulated
–
–
–
–
–
5
Pulse and Cycle Characteristics
•Phase shape
–Sinusoidal
–Rectangular
–Spike
•Pulse
•Finite period of charged particle _______________, separated from other pulses by a
finite _____________ during which ____ current flows
•Made up of one or more _____________
•Pulse named by _________________ of phases
–Monophasic
•
•Current
flows in ____ direction only.
–Biphasic
•
•Current
flows in _______ directions.
–Polyphasic
•
6
•Phase charge
–Electrical charge of a ____________ phase, expressed as
coulombs
–Time integral; result of both amplitude and width
•Pulse charge
–Electrical ____________ of a single ______________
–
 Pulse symmetry
•Applies only to biphasic pulse
•Relationship between ___________________ of the two phases
•Symmetrical:
•Asymmetrical:
 Pulse charge balance
•Applies only to biphasic pulses
•Charges of two phases equal (balanced) or different
•Independent of whether the phases are symmetrical
•Train
–A _________________ _____________________ series of pulses at a fixed frequency
–Polyphasic
–Pure AC
•Burst
–Finite series of ____________ flowing for a finite _____________ period followed by
no _________________ flow
•Think of it as turning a pulse train or AC current on and off.
–Burst interval
•
–Interburst interval
•
7
Duty Cycle
–Ratio of time _____ vs. total time
•Thus current with an on time of 10 msec and an off time of 40 msec would have
a 20% duty cycle
Current Timing Modulation
•Phase duration
– ___________ during which current flows in a _________________ direction
•Rise time
– ___________ from beginning of a phase until maximum _____________________
•Decay time
– ___________ from maximal amplitude to end of a ________________
•Pulse width (pulse duration)
– ___________ required for each ___________ to complete its _____________
–Reported in microseconds or milliseconds
•Short pulse duration: <150 µsec
•Long pulse duration: >200 µsec
•Interpulse interval
– ___________ between successive ____________
8
•Period
–Beginning of the ____________ to the beginning of the subsequent ______________
•Pulse rate (frequency)
–Rate at which _____________ are repeated
–Pulses per second
•Amplitude (______________, ______________)
–Measured in two ways
• __________________ delivered to the electrodes
•Current flowing through the _____________
•Peak current
–Highest ___________________ of the pulse
•Average current
–Average _____________ of a ____________
–Computed in two ways
•Average current during the _____________
•Average current during the ______________
•Includes the ______ time between pulses
Stimulation Pattern
•Constant stimulation
– _________________ of successive pulses (or cycles) is the same
•Surged stimulation
–Individual _______________ gradually increase from __________ to a maximum
preset ___________________
•Surge characteristics
•Ramp up
–Time during which the intensity _____________________
•Plateau
–Time during which pulses remain at _________________ preset ___________
•Ramp down
–Time during which the intensity _____________________
9
•Time on
–Time during which _________________ flows; from the _________________
to the _____________ of a surge
•Time off
–Time during which current does ______ flow; time _________________ surges
Commonly Used Wave Forms
•Modulation of DC and AC currents produces a variety of output forms.
•Direct (galvanic) wave form
–Pure __________ current
–Used for ________________________
•Interrupted DC wave form
– __________________________ flow caused by ___________ and _______________
turning on and off of the current
–Also called modified square wave
–Similar to _____ but modulated from AC input current
– ____ and _____ times are not necessarily equal
•Sinusoidal wave form
–Pure __________ current
–Polyphasic, symmetrical, balanced, sinusoidal
10
•Faradic wave form
–Induced ______________________ ______ current
–Biphasic, asymmetric, unbalanced, spiked
–Positive portion: ___________ duration,____________ amplitude, and spiked
–Negative portion: __________ duration, _________ amplitude, and curved
–Faradic has a double meaning
–Used to describe any ____ current
–Similar to galvanic as a synonym for DC current
•Biphasic wave form
–Symmetrical, balanced, rectangular, pulsed
•Twin pulse wave form
–Monophasic, pulsed, twin spiked
–Common wave form of high-volt _______________ simulators
–Has been called high-volt galvanic and pulsed direct current
–However, not _____ current
11
•Russian wave form
–Polyphasic, symmetrical, sinusoidal, burst
•Interferential wave form
–Symmetrical,
sinusoidal, high frequency (2000–5000 Hz) AC
_____ channels, with different _____________________, used simultaneously
–Two currents cause a ______________ _________________ _________________
modulation
–
•Interferential wave form: current amplitude modulation
•Two identical currents (a)
•Two opposite currents (b)
•Two offset currents (c)
12