david powler

The R.M.S. Value of an Alternating Current (or
Voltage)
© David Hoult 2009
© David Hoult 2009
If an a.c. supply is connected to a component of
resistance R, the instantaneous power dissipated
is given by
© David Hoult 2009
If an a.c. supply is connected to a component of
resistance R, the instantaneous power dissipated
is given by power = i2 R
© David Hoult 2009
© David Hoult 2009
© David Hoult 2009
The mean (average) power is given by
© David Hoult 2009
The mean (average) power is given by
mean power = (mean value of i2) R
© David Hoult 2009
The mean value of i2 is
© David Hoult 2009
The mean value of
i2
I2
is
2
© David Hoult 2009
The square root of this figure indicates the
effective value of the alternating current
© David Hoult 2009
The square root of this figure indicates the
effective value of the alternating current
r.m.s. = root mean square
© David Hoult 2009
© David Hoult 2009
Irms =
I
2
where I is the maximum (or peak) value of the a.c.
© David Hoult 2009
Resistor Examples
Contact leads
Symbol for resistor
Resistor
Resistor Labels
• Wire-wound resistors have a label indicating resistance and power ratings.
• A majority of resistors have color bars to indicate their resistance magnitude.
• There are usually 4 to 6 bands of color on a resistor. As shown in the figure
below, the right most color bar indicates the resistor reliability, however, some
resistor use this bar to indicate the tolerance. The color bar immediately left
to the tolerance bar (C), indicates the multipliers (in tens). To the left of the
multiplier bar are the digits, starting from the last digit to the first digit.
Resistor value = AB 10  tol %()
C
Resistor Color Codes
Band color
Digit
Multiplier
Black
0
X1
Brown
1
X10
Color
Tolerance
Red
2
X100
Brown
1%
Orange
3
X1000
Red
2%
Yellow
4
X10000
Green
5
X100000
Blue
6
X1000000
Gold
5%
Silver
10%
Purple
7
X10000000
None
±20%
Grey
8
X100000000
White
9
X1000000000
Silver
-
x.01
Gold
-
x.1
6. Band rengi direncin değerinin sıcaklıkla ne kadar değiştiğini belirtir.
Birimi PPM/C dir. Yani C (santigrat derecede) milyon başına değişim
demektir (PPM=part per million)
∆R : Dirençteki değişim miktarı (ohm)
TCR : Sıcaklık katsayısı (PPM/ oC)
R0 : T0 da ölçülen direnç değeri (ohm)
R :T de ölçülen direnç değeri (ohm)
T0 : İlk Sıcaklık (oC)
T :Son sıcaklık (oC)
Örnek: Sıcaklık katsayısı 150 PPM/ oC olan 1Kohm luk bir direncin
ortam sıcaklığı 25 oC den 30 oC ‘ye çıkarsa direnç değeri ne kadar
değişir.
Example
•
•
•
•
The first band is yellow, so the first digit is 4
The second band is violet, so the second digit is 7
The third band is red, so the multiplier is10 2
Resistor value is 47 102  5%()
Source Transformations
Source Transformations
Source Transformations
Source Transformations
Source Transformations
Source Transformations
Source Transformations
Source Transformations