ELT M1 S14 - 5
Transcript of ELT M1 S14 - 5
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RECAP
The Coulomb Force (fundamental force)
Voltage Ohms law
Resistance
Power
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Charge
Elementary charge e = 1.602 10 C
charge Q2distance r
charge Q1
Force between charges:
vacuum permittivity 8.854 10
Current: how many electrons are flowing by per time unit.
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Voltage
Current is driven by a voltage difference between two
points, i.e. a voltage difference tries to drive electrons to
the lower voltage point in order to eliminate thedifference.
Voltage (potential difference) is measured in Volt = Joule /
Coulomb, this is how much work each electron can
perform.The higher the voltage the harder are the electrons
pushed away from the higher voltage point. (like a
waterfall)
Voltage is relative by nature. Voltage makes only sensewhen compared/measured to a reference point. One
single point does not have a defined voltage.
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Ohms law
A voltage difference U (Volt) between two points causes a current I
to flow.
It is found that current is proportional to the voltage.
The (inverse) constant of proportionality is called the resistance R.
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1
1A 1000 1
1000
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1 1M
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Resistance of a regular shaped conductor
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Power
=
Voltage U
Resistor R
Current I
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Practical implementation
of resistors
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WIRE-WOUND RESISTORS (1)
Power dissipation: 5W 500W, resistance: typical < 1k
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WIRE-WOUND RESISTORS (2)
Power dissipation: 4W 17W, resistance: typical < 22k
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STANDARD LEADED CARBON OR METAL FILM RESISTORS
Power dissipation: 0.25W-3W, resistance: ~0.01 ~1G
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arbon Resistor Metal Film Resistors
+ cheap
+ can withstand higher
voltage
+ higher precision
+ less sensitive to changes in
temperature
+ lower noise
- larger tolerances
- higher noise floor
- more prone to aging
- a bit more expensive
(although the difference
flattens out)
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SURFACE MOUNTED DEVICE (SMD) RESISTORS
3mm
Power dissipation: 0.25W-3W, resistance: ~0.01 ~1G
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SURFACE MOUNTED DEVICE (SMD) RESISTORS
Power dissipation: 0.0625W-2W, resistance: 0 ~1T
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APPLICATION OF TEMPERATURE
COEFFICIENT
Temperature measurement
Some materials, e.g. platinum, have linear temperaturedependency
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Resistance vs. Temperature Pt100 element
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Reference: Lee, R. C, Dougherty, W., Electrical Injury:,
IEEE Trans. Dielectrics and Electrical Insulation, Vol. 10,No. 5, 2003
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