Download V - Preparing for Anaesthesia Exams

Electricity And
Electrical Safety
Dr Shiv Kumar Singh
Consultant Anaesthesia
Royal Liverpool University
Hospital
[email protected]
[email protected]
“Knowledge is of two kinds: We know
a subject ourselves, or we know where
we can find information about it."
Samuel Johnson
Today’s Lec
•  Basics of electricity
•  Electrical and electronic components in
anaesthesia equipments
•  Electrical Safety: Principles and examples
•  Electrical symbols: What do they mean
and importance
•  Diathermy: Principle and electrical safety
issues
Basics of Electricity
Conductors, insulators and
semiconductors
Current,Voltage & Resistance
Insulator
Conductor
ELECTRONIC CLASSIFICATION OF SOLIDS
Semi-conductor
Conductors, Insulators and Semi-conductors
Conduction band
Conduction band
Forbidden band
Valence band
Valence band
Conduction band
Forbidden band
Valence band
Electric Field Direction
Conduction Band
Hole
Forbidden Band
Valence Band
(Filled)
COUPLING
HOLES
P TYPE
SEMICONDUCTOR
ELECTRONS
N TYPE
SEMICONDUCTOR
Current flow
Electrons
Relation between current,
voltage and resistance ?
Ohm’s law
Resistance
Potential
difference
T
Flow
V
I =
R
V
R=
--I
V
I
V
I=
R
--R
V=IXR
The power supply
Generator
Turbine
Steam
Water
Boiler
Condenser
Electricity
Magnet
Live 1
Induction
Coils
Live 2
Live 3
Neutral
Generator
POWER
Power
Station
STATION
toaster
Substation
Earth
POWER
Power
Station
STATION
Socket
Fuse
Live
Substation
Neutral
Plug
Earth
Soil
R.M.S and Peak voltage
•  U.K main Voltage:
230V [ 253 V (+10%) and 216 V (-6%)]
•  R.M.S value of the voltage.
•  The Peak Voltage:
1.413 (√2) x 240 V i.e 340 V
Square
P
o
t
e
n
t
i
a
l
Mean
Root mean square potential
Square
root
Electricity
Components & applications
Cell
Capacitor
Resistor
Battery
Cell
Resistor
Battery
Transformer
Capacitor
Inductor
Diode
Amplifier
Transformer
Inductor
Capacitors
V
Insulator
Capacitor
plates
++++++++ ++
Q α V Capacitance (C) = Q / V
1 F = 1 Coulomb / 1 Volt
Separation
d
Area (A)
Area
A
Capacitance
α
Separation (d)
Charge Q
Voltage V
Energy stored
Q
E=QxV
V
Q α V  C = Q/V or Q =C X V
Area = Work done
=½QV
But Q = CV  Energy stored = ½ CV2
Charge
Q
V
Insulator
++++++++
E=½QxV
Voltage V
Q α V  C = Q/V or Q =C X V
Area = Work done
=½QV
But Q = CV  Energy stored (E) = ½ CV2
Capacitance and interference
50 Hz
Capacitance link
INSULATOR
CONDUCTOR
Inductors
Inductors
Magnetic field
Continuously
varying
magnetic field
Alternating
Current
Inductor
Switch
Inductance and interference
Diathermy
Oscillator
MAGNETIC
FIELD
CAPACITOR
INDUCTOR
CAPACITOR
INDUCTOR
Reactance and Frequency
Capacitors
And
Inductors
Reactance
Inductors
Capacitor
Frequency
Transformers
Application of Inductance
PRIMARY COIL
SECONDARY COIL
VP
VS
NP
NS
VP / VS = NP/NS
VS = VP x NS/NP
240 V
240 V
240 V
240 V
120 V
480 V
STEP
DOWN
STEP
UP
Diodes
Semiconductors
Diodes
Bridge Rectifier
Positive
cycle
Input
Output
Negative
cycle
Defibrillators
Circuit
Waveforms
Charging
Diode
5000-9000 V
Inductor
Diode
5000-9000 V
Inductor
Monophasic
Current (Amps)
50
Damped sine wave
40
30
20
10
0
-10
-20
0
4
8
Time (msecs)
12
Biphasic
Current (Amps)
Biphasic Truncated Exponential
- BTE (SMART, Philips)
50
40
30
20
10
0
-10
-20
0
4
8
Time (msecs)
12
Biphasic
Current (Amps)
Rectilinear Biphasic waveform
(Zoll)
50
40
30
20
10
0
-10
-20
0
4
8
Time (msecs)
12
Biological signals
Amplifiers
&
Filters
Amplifiers
Device that responds to a small input signal
(current, voltage, power)
and delivers a larger output signal
that contains the essential waveform features of
the input signal.
Amp
Single ended pre-amplifier
Output
Input
Ref earth
Amp
Single ended pre-amplifier
Output
Input
Ref earth
Amp
Differential / balanced pre-amplifier
Input
Inverting
NonInverting
Ref earth
Amp
Output
Differential / balanced pre-amplifier
Inputs
Amp
Output
Ref earth
Noise
Output
Input
Inv
Non
Inv
Amp
Inv
Non
Inv
Amp
Differential / balanced pre-amplifier
Input
-
+
-
-
RA
I
LA
II
III
LL
+
+
Ref earth
Output
Amp
Interference
Inv
Non
Inv
Amp
+
COMMON MODE REJECTION
Filters
What are they?
Why do we need them?
Filters
Arrangement of electronic components
that allow only those electric waves
lying within a certain range, or band, of
frequencies to pass
and block others
Output
Frequency
Output
Frequency
Output
Frequency
High f
Amplifier
Low f
Filters & amplifiers
Channel ? Filter
Volume? Amplifier
Resistances
Wheatstone Bridge
A
R1
R3
D
C
R2
R4
B
A
R1
R3
R2
R4
B
R1
R3
=
R2
R4
R1
Rv
R2
R1
Rv
=
R2 Rm
Rm =
R2
R1
Rv
Rm
R1
Rv
R2
Rm
R1
R2
Rv
Rm
R1
R2
Rv
Rm
R1
Rv
R2
Rm
12Kg
20 Kg
?
R1
RV
Pressure
R2
R1
RV
=
R2 RM
RM = RV
RM
Saline
Diaphragm
R2
R1
Strain gauge
SIMPLE CIRCUIT
BULB
-
+
SWITCH
BATTERY