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impedance
impedance. what is it? how do we determine it? how do we represent it? lots of questions, thats for sure. we in the engineering field specify resistance as the force which resists a circuits ability to allow a current to flow. since voltage is the PRESENCE of electricity, CURRENT is ELECTRONS in motion. there are 2 different types of voltage. DC or direct current, is where the voltage is always the same. Right now, your coumputer is producing +5 volts DC to your CPU. However, the voltage coming out of your wall outlet ( where your computer is plugged in ) is 120 Volts AC or ALTERNATING CURRENT. if you try to plug a Pentium 4 into the wall -- well, you just lost a lot of money. somehow, we convert AC to DC. a power supply will do this for us. since a power supply has components that have resistance to DC and AC ( AC resistance is called IMPEDANCE ), maybe we can look at a power supply to see how all this impedance stuff works.
for starters, you're going to have to know TRIGONOMITRY. Simply put, there is a type of triangle called a RIGHT TRIANGLE. the reason we use right triangles is because we know 1 of the angles ( one angle of a right triangle is 90 degrees ) and the hypoteneuse. if we looked at a circuit as DC resistance being the X Axis of a grid, and AC resistance as being the Y Axis, then we can apply trig functions to determine the IMPEDANCE of the given circuit.
this type of GRAPH is called a CARTESIAN type with X and Y coordinates. in electronics, we can apply this type of graph to represent AC and DC resistances. thus
the phase angle theta simply tells us how much of the circuit is of the following 3 quantities :
Purely Resistive : means that the circuit has just resistors Purely Inductive : means the circuit has lots of inductors Purely Capacitive : means the circuit has Lots of capacitors
or some combination of the three types. So you may ask, whats this got to do with the price of tea in china ? well, in say a power supply, if we have lots of transformer, then we LOSE power out of the supply. if wehave lots of resistor, we get whats called MAXIMUM POWER TRANSFER. Pin = Pout this is called the efficiency of a circuit. when we place reactive components ( inductors and capacitors ) into a circuit, we get impedance. impedance has 2 components -- resistance and reactance. if we were to take the square root of the sum of the squares, we get impedance. this corresponds to the hypotenuse of a right triangle. the phase angle of the circuit, called Theta, tells us how much and what type of impedancew is in the circuit. if the phase angle is positive ( 0 - 179 degrees ) the circuit is more inductive. if the phase angle is negative ( 180 - 359 degrees ) the circuit is more capacitive. well, how do we fit this all together?
ideally, we want the value of Y to be much smaller than X. remember, AC resistance changes with frequency, inductance and capacitance. keeping the inductive and capactitive resistance values as low as possible in a reactive circuit will give you a greater power transfer and you will be saving that power for other things. or save a few dollars.
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impedance
impedance. what is it? how do we determine it? how do we represent it? lots of questions, thats for sure. we in the engineering field specify resistance as the force which resists a circuits ability to allow a current to flow. since voltage is the PRESENCE of electricity, CURRENT is ELECTRONS in motion. there are 2 different types of voltage. DC or direct current, is where the voltage is always the same. Right now, your coumputer is producing +5 volts DC to your CPU. However, the voltage coming out of your wall outlet ( where your computer is plugged in ) is 120 Volts AC or ALTERNATING CURRENT. if you try to plug a Pentium 4 into the wall -- well, you just lost a lot of money. somehow, we convert AC to DC. a power supply will do this for us. since a power supply has components that have resistance to DC and AC ( AC resistance is called IMPEDANCE ), maybe we can look at a power supply to see how all this impedance stuff works.
for starters, you're going to have to know TRIGONOMITRY. Simply put, there is a type of triangle called a RIGHT TRIANGLE. the reason we use right triangles is because we know 1 of the angles ( one angle of a right triangle is 90 degrees ) and the hypoteneuse. if we looked at a circuit as DC resistance being the X Axis of a grid, and AC resistance as being the Y Axis, then we can apply trig functions to determine the IMPEDANCE of the given circuit.
+Y
|
|
|
|
-X --------------------- +X
|
|
|
|
-Y
this type of GRAPH is called a CARTESIAN type with X and Y coordinates. in electronics, we can apply this type of graph to represent AC and DC resistances. thus
+AC resistance
| * Z or impedance
| /
| /
|/ <<phase angle Theta
-DC Resistance ----------- +DC Resistance
|
|
|
|
-AC resistance
the phase angle theta simply tells us how much of the circuit is of the following 3 quantities :
Purely Resistive : means that the circuit has just resistors Purely Inductive : means the circuit has lots of inductors Purely Capacitive : means the circuit has Lots of capacitors
or some combination of the three types. So you may ask, whats this got to do with the price of tea in china ? well, in say a power supply, if we have lots of transformer, then we LOSE power out of the supply. if wehave lots of resistor, we get whats called MAXIMUM POWER TRANSFER. Pin = Pout this is called the efficiency of a circuit. when we place reactive components ( inductors and capacitors ) into a circuit, we get impedance. impedance has 2 components -- resistance and reactance. if we were to take the square root of the sum of the squares, we get impedance. this corresponds to the hypotenuse of a right triangle. the phase angle of the circuit, called Theta, tells us how much and what type of impedancew is in the circuit. if the phase angle is positive ( 0 - 179 degrees ) the circuit is more inductive. if the phase angle is negative ( 180 - 359 degrees ) the circuit is more capacitive. well, how do we fit this all together?
Z = impedance
X = DC resistance
Y = AC resistance
Z = SQRT( (X^2) + (Y^2) )
ideally, we want the value of Y to be much smaller than X. remember, AC resistance changes with frequency, inductance and capacitance. keeping the inductive and capactitive resistance values as low as possible in a reactive circuit will give you a greater power transfer and you will be saving that power for other things. or save a few dollars.
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