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Arieh Nachum
Magnetism,
Induction and
Transformers
EB-3124
Arieh Nachum
Magnetism,
Induction and
Transformers
EB-3124
1_11
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translated, re-edited or broadcast without prior agreement in writing
from DEGEM Systems.
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 E-mail: [email protected]  Site: www.degem.com 
I
Contents
Preface ............................................................................................................. II
Experiment 1 – Electromagnet and Solenoid ............................................... 1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
Magnet................................................................................................... 1
Magnetic fields ...................................................................................... 3
Electricity and magnetism..................................................................... 4
Magnetic self and mutual induction ...................................................... 6
Magnetic penetrability .......................................................................... 8
Magnetic Hystheresis ............................................................................ 9
Electromagnet ..................................................................................... 10
The relay.............................................................................................. 11
Solenoid............................................................................................... 11
PWM signal......................................................................................... 12
Experiment 2 – The Transformer ................................................................ 23
2.1
2.2
Induced drive electro power................................................................ 23
The transformer ................................................................................... 25
Experiment 3 – Troubleshooting ................................................................. 31
EB-3124 – Magnetism, Induction and Transformers
II
Preface
The experiments in this manual are meant to be run on the experiment board
EB-3124 with the Universal Training System EB-3100.
The EB-3100 includes:
 5 voltages power supply (+12V, +5V, –5V, –12V and –12V to +12V
variable voltage).
 2 voltmeters.
 Ampere-meter.
 Frequency counters up to 1MHz.
 Logic probe (High, Low, Open, Pulse, Memory).
 Logic analyzer with 8 digital inputs and trigger input.
 Two channel oscilloscope (with spectrum analysis while connecting to the
PC).
 Function generator (sine, triangle and square wave signals) up to 1MHz.
 3.2" color graphic display with touch panel for signal and measurement
display.
 USB wire communication with the PC.
 20 key terminal keyboard.
 10 relays for switching the plug-in boards or for planting faults.
 48 pin industrial very low resistance connector for plug-in boards'
connection.
 Transparent sturdy cover covers the upper part of the plug-in boards in
order to protect the board's components that should be protected.
EB-3124 – Magnetism, Induction and Transformers
III
The EB-3100 boards are:
Electricity and Electronics
EB-3121
Ohm and Kirchoff Laws and DC circuits
EB-3122
Norton, thevenin and superposition
EB-3123
AC circuits, signals and filters
EB-3124
Magnetism, electromagnetism, induction and transformers
Semiconductor Devices
EB-3125
Diodes, Zener, bipolar and FET transistors characteristics and DC circuits
EB-3126
Bipolar and FET transistor amplifiers
EB-3127
Industrial semiconductors – SCR, Triac, Diac and PUT
EB-3128
Optoelectronic semiconductors – LED, phototransistor, LDR, 7-SEG.
Linear Electronics
EB-3131
Inverter, non-inverter, summing, difference operational amplifiers
EB-3132
Comparators, integrator, differentiator, filter operational amplifiers
EB-3135
Power amplifiers
EB-3136
Power supplies and regulators
EB-3137
Oscillators, filters and tuned amplifiers
Motors, Generators and Inverters
EB-3141
Analog, PWM DC motor speed control, step motor control, generators
EB-3142
Motor control – optical, Hall effect, motor closed control
EB-3143
AC-DC and DC-AC conversion circuits
EB-3144
3 Phase motor control
Digital Logic and Programmable Device
EB-3151
AND, OR, NOT, NAND, NOR, XOR logic components & Boolean algebra
EB-3152
Decoders, multiplexers and adders
EB-3153
Flip-flops, registers, and counters sequential logic circuits
EB-3154
555, ADC, DAC circuits
EB-3155
Logic families
Microprocessor/Microcontroller Technology
EB-3191
Introduction to microprocessors and microcontrollers
EB-3124 – Magnetism, Induction and Transformers
IV
The EB-3124 is connected to the EB-3100 via a 48 pin industrial connector.
It has a built-in microcontroller that identifies (for the EB-3100 system) the
experiment board when it is being plugged into the system, and starts a selfdiagnostic automatically.
The following figure describes the EB-3124 experiment board.
B1
B2
+12V
+12V
N.C.
R2
10K
+12V
COM
N.O.
D
G
AC
Power
Supply
Relay
S
+12V
R1
1M
Electromagnet
50 60
Hz
PWM
Signal
B4
B3
+12V
Switch
Solenoid
Pushbutton
EB-3124 Panel Layout
EB-3124 – Magnetism, Induction and Transformers
V
The experiment method:
The system uses an external switching power supply for safety reasons. The
power supply low voltage output is converted to the 5 voltages by linear
regulators for noise reduction.
Two potentiometers on the panel are used to setup the variable voltage and the
function generator amplitude.
The system cut-off the voltages in overload and displays a massage about that.
The plug-in cards are connected directly to system without any flat cable for
noise and resistance reduction.
The 10 relays are change over relays that can switch active and passive
components.
Every selecting of a relay configuration is saved in a non-volatile memory
located on the connected plug-in card.
The components are located on the board with silk screen print of the
analytical circuit and component symbols. The central part of the
experimenting board includes all the circuit block drawings and all the hands
on components, test points and banana sockets.
The protected components are located on the circuit board upper side, clearly
visible to the student and protected by a sturdy transparent cover.
On plugging the experiment board, it sends a message to the EB-3100 which
includes the board's number and which of its block are faulty. If there is a
faulty module (B1-B8), it will be displayed on the screen.
The experiment board checks itself while it is being plugged. This is why,
during the plug-in, any banana wire should not be connected on the
experiment board.
5 LEDs should turn ON on the top right.
EB-3124 – Magnetism, Induction and Transformers
VI
The system includes 5 power supply outputs. The system checks these
voltages and turns ON the LEDs accordingly.
+12V
+5V
–5V
–12V
–
–
–
–
Red LED
Orange LED
Yellow LED
Green LED
The fifth voltage is a variable voltage (Vvar) controlled by a slider
potentiometer.
The LED of the Vvar is both green and red: when the Vvar voltage is positive
– the color is red and when it is negative – the color is green.
There are no outlets for the power supply voltages on the
The voltages are supplied only to the 48 pin connector.
TSP-3100 panel.
The experiment boards take these voltages from the 48 pin connector.
EB-3100 Screens
The system has 3 operating screens: DVM, Oscilloscope and Faults.
Moving from one screen to another is done by the Options/Graph key.
The keyboard is always at Num Lock position.
The keys can also be used as function keys. In order to do so, we have to press
once on the Num Lock key and then on the required key. The keyboard
returns automatically to Num Lock mode.
On scope screen, pressing the Num Lock key and then the Digital key will
change the screen to Digital signal screen display.
Pressing the Num Lock key and then the Analog key will change the screen to
Analog signal screen display.
EB-3124 – Magnetism, Induction and Transformers
VII
DVM Screen
DVM
V1 [V]
0.00
V2–V1 [V]
0.00
Fout [KHz]
5.00
V2 [V]
0.00
I [mA]
0.0
Cin [Hz]
5.00
I (+5V) [mA]
I (+12V) [mA]
0
0
I (–5V) [mA]
I (–12V) [mA]
0
0
Num Lock
V1 is the voltage measured between V1 inlet and GND.
V2 is the voltage measured between V2 inlet and GND.
V2–V1 is the voltage measured between V1 and V2. It enables us to measure
floating voltage.
I is the current measured between A+ and A– inlets.
Cin displays the frequency is measured in the Cin inlet.
The EB-3100 includes a function generator.
The frequency of the function generator is displayed in the Fout field and can
be set by the arrow keys or by typing the required values.
The square wave outlet is marked with the sign
.
Near the analog signal outlet there is a sine/triangle switch marked with the
signs
/
.
EB-3124 – Magnetism, Induction and Transformers
VIII
Scope Screen
CH1 3.0VCH2
3.0V t 50s
CH1
1.0V
Num Lock Analog Run
The scope and the display parameters (CH1 Volt/div, CH2 Volt/div, time base
Sec/div, Trigger Channel, Trigger rise/fall, Trigger Level) appear on the
bottom of the screen.
The Up and Down arrow keys highlight one of the fields below.
The required field can be selected by touching it and can be changed by the
Up and Down arrows.
The function generator amplitude is changed by the amplitude potentiometer.
The sampling and display can be stopped by pressing the Num Lock key and
then pressing the Stop (8) key.
Performing a single sampling is done by pressing the Num Lock key and then
pressing the Single (9) key.
Running again the sampling is done by pressing the Num Lock key and then
pressing the Run (7) key.
EB-3124 – Magnetism, Induction and Transformers
IX
Digital Screen
Pressing the Num Lock key and then the Digital key on scope screen displays
the Digital screen.
D0
D1
D2
D3
D4
D5
D6
D7
D0
D1
D2
D3
D4
D5
D6
D7
t 50s
TRIG
Num Lock Digital Run
Check that.
The logic analyzer includes 8 digital inlets and one trigger signal inlet.
The controller waits for trigger and when it encounters a trigger pulse it
samples the 8 digital inputs.
If a trigger pulse is not found the sampling will be according to the time base.
The sampling and display can be stopped by pressing the Num Lock key and
then pressing the Stop (8) key.
Performing a single sampling is done by pressing the Num Lock key and then
pressing the Single (9) key.
Running again the sampling is done by pressing the Num Lock key and then
pressing the Run (7) key.
EB-3124 – Magnetism, Induction and Transformers
X
Logic Probe
The EB-3100 Logic Probe includes 5 LEDs indicating the Logic Probe (LP)
input state – High, Low, Open (unconnected), Pulses and Memory (registering
single pulse).
The Logic Probe also has a TTL/CMOS switch that determines which logic
level is selected.
When the LP is connected to a point with a voltage blow 0.8V (for TTL) or
1.3V (for CMOS), the L green LED should turn ON.
When the LP is connected to a point with a voltage above 2.0V (for TTL) or
3.7V (for CMOS), the H red LED should turn ON.
The voltage between these levels turns ON the OP orange LED.
Fault Screen
The EB-3100 includes 10 relays for fault insertion or for switching external
components.
The fault screen is selected by the Options/Graph key.
FAULTS
Please choose
Fault No.: 0–9
Activated fault
Number: 0
Num Lock
Typing a fault number and pressing ENTER operates the required relay for the
required fault.
Fault No. 0 means No Fault.
Which relay creates the required fault is registered in the plug-in experiment
board controller.
EB-3124 – Magnetism, Induction and Transformers
XI
On entering a fault number, the system addresses the experiment board
controller and asks for the relay number. After that, it executes the required
fault.
The experiment board controller saves the last registered fault number in its
memory. This memory is non-volatile.
This is why the system does not allow us to enter a fault number when no
experiment board is plugged.
When an experiment board that a certain fault (other than zero) is registered in
its memory is plugged into the system, a warning message appears on the
system's screen.
This feature enables the teacher to supply the students various experiment
boards with planted faults for troubleshooting.
Note:
It is recommended (unless it is otherwise required), to return the
experiment board fault number to zero before unplugging it.
EB-3124 – Magnetism, Induction and Transformers
XII
EB-3124 – Magnetism, Induction and Transformers
1
Experiment 1 – Electromagnet and Solenoid
Objectives:
 Introducing the magnet.
 Electromagnet and magnetic residue.
 Introducing the solenoid.
Equipment Required:
 EB-3100
 EB-3124
 Banana wires
Discussion:
1.1
Magnet
More than two thousand years ago, the Greeks discovered stones attracted to
iron in the city Magnesia in Turkey. They called these stones magnets after the
name of the isle.
In time it became apparent that magnet bars on an axle or hanging on a string,
will turn and always to arrange in the same direction. One side will always
turn to the North and the other to the South. This is why the magnet edges are
called poles – the North Pole (turning to the north side) and the South Pole
(turning to the south side).
The compass is actually a magnet bar floating in liquid which allows its
turning towards the north.
Another phenomenon which was discovered is that identical poles reject each
other and opposite poles attract each other. The North Pole rejects the north
and attracts the south and the South Pole rejects the south and attracts the
north.
EB-3124 – Magnetism, Induction and Transformers
2
The North Pole and the South Pole attract and are attracted to iron. The reason
for that is derived from the iron's character. Putting an iron near a magnet will
turn it to a magnet. The iron has magnetism character which is called
Ferromagnetism.
Ferrom = iron
Other matters with magnetism characters are called Ferromagnetism materials.
Each matter in nature contains tiny magnets. Each magnet has North and
South poles. The magnets are in disorder, thus the North poles cancel the
influence of the South poles and vice versa.
N – North
S – South
N S
Single
Molecule
Figure 1-1
In a magnet a large part of the tiny magnets are organized in a orderly fashion.
Figure 1-2
On the north side of the magnet, we find poles of the north kind and on the
south side, we find poles of the south kind. At the middle of the magnet, there
is no magnetic pull because the poles are canceling each other.
EB-3124 – Magnetism, Induction and Transformers
3
In iron, a large part of the internal magnets can be moved. When we put an
iron near a magnet, the internal magnets align in the right direction. If we
bring the North Pole of the magnet near an iron, the internal magnets will
align so that their South Poles will turn towards the magnet and the North
Poles will turn in the opposite direction (in order to get away from the North
Pole). The iron becomes a magnet, in an opposite polarity to the magnet we
put near it and so it is attracted to it.
If we bring one iron near another magnetize iron, the first iron will be drawn
to the magnet in the same way.
1.2
Magnetic fields
The magnetic attraction does not depend on any middle. It exists also in space.
The magnetic attraction grows wick as it draws away from the magnet poles.
The poles magnetic influence operates in all directions. On the other side, a
magnet near one of the poles will be influenced more from this pole then from
the distanced pole. If we put iron dust on a platform around the magnet, these
iron grains will become magnets. If we shake the platform the iron grains will
be arranged around the magnet in the following way:
N
S
Figure 1-3
The magnets will arrange along the line described above. Those in the center
will feel an equal influence of both poles, thus they will arrange in parallel to
the magnet rod. The others will turn according to their closeness to one of the
poles.
These lines describe the magnetic attraction influence and are called the
magnetic field lines. The magnetic field is the magnetic influence area.
EB-3124 – Magnetism, Induction and Transformers
4
1.3
Electricity and magnetism
In the past it was considered that the magnetic characters of matter does not
relate to other characters. In the 19th century it was discovered that there is a
relationship between magnetism and electric current. When a compass was put
near a conductor with electric current, the compass changed its direction
according to its location around the current carrying conductor.
Magnetic
Compasses
Electric
Current
Figure 1-4
Around the conductor with the electric current a circular magnetic field was
created. The magnetic field direction is according to the law called "the law of
the right hand".
Figure 1-5
When the thumb points in the direction of the current in the conductor, the
magnetic field lines move according to the fingers direction.
EB-3124 – Magnetism, Induction and Transformers
5
If we bend the electric conductor to a ring shape and current will flow in the
conductor, we will get magnetic filed lines centralization inside the ring which
all in the same direction.
Conductor Wire carrying current
Figure 1-6
Inside the ring, which is called bind, we get a stronger magnetic field. If we
will create a large number of binds from the conductor, we will get an electric
coil with a strong magnetic field in its center.
We see that a magnetic field is derived from electrical charges movement.
Even the tiny magnets inside the matter are derived from charges movement.
The charges which move in the matter are called electrons.
The electron has two types of circular movement. One movement it rotates
around the nucleus and the second movement it rotates around itself. The
rotation around itself is called Spin. The spin creates the stronger magnetic
field.
In a Ferromagnetic matter, external magnetic influence causes the electrons to
align, so that the magnetic field created by their spin, matches the external
magnetic field lines.
EB-3124 – Magnetism, Induction and Transformers
6
1.4
Magnetic self and mutual induction
As we saw in the previous section, a magnetic field appears around the current
carrying conductor. This magnetic field is called magnetic induction (of the
current). The magnetic field units are Weber. To express the size of the
magnetic field in a certain point, we use the concept magnetic flow and it
depends on its distance from the conductor according to the following law:
B0 
 0I
2a
B - The magnetic field flow density at a certain point
a
I
- The point distance from the conductor
- The current volume in the conductor
0 - A constant called magnetic frequency
 Wb 
 m 2 
[n2[
[A]
 Wb 
 A  m 
In a circular bind, the magnetic flow density in the bind incision is consistent
in all the incision points and its value is calculated according to the following
formula:
B0 
 0I
2r
r – radium of the circular bind.
In a coil with N dense binds we will get magnetic flow density:
B0 
 0 NI
2r
If the coil is 1 length, we will get magnetic flow density according to the
formula:
B0   0
NI
l
The last formula relates to the magnetic flow density of a 1 length coil, which
is much longer than its radius and not near the coil edges. This coil is called
solenoid.
EB-3124 – Magnetism, Induction and Transformers
7
The magnetic field lines in a solenoid look as follows:
c
d
x
b
a
Figure 1-7
From the outside, the solenoid behavior is similar to the behavior of the
ordinary magnet. The difference is that inside the solenoid binds there is a
magnetic field with a defined direction.
If we create a coil in circular wrapping we will get a component called toroid.
Figure 1-8
In this coil, all the magnetic flow flows inside the coil and does not come out.
In spite the current flow in the coil binds, the magnetic field is not detected
outside the coil.
EB-3124 – Magnetism, Induction and Transformers
8
1.5
Magnetic penetrability
The magnetic flaw density formula in the coil:
B0   0
NI
l
Relates to a Brick coil (the result is similar in the air).
NI
l
causes the magnetic field. It is marked by the letter H and called the
magnetic power of the coil.
H
NI
l
The magnetic flaw density depends on the magnetic power and the magnetic
penetrability of the Brick medium.
B0  0H
If we insert Ferromagnetic matter (matter that can be magnetized) into the
coil, this matter will becomes a magnet and amplify the magnetic flaw,
according to the Ferromagnetic characteristics of the matter.
B  K m 0
NI
 K m 0 H
l
Km is the relative penetrability of the matter.
The Km0 product is defined as the matter penetrability and is marked with
the letter .
  K m 0
B  H
EB-3124 – Magnetism, Induction and Transformers
9
1.6
Magnetic Hystheresis
The formula:
B  H
When:
H
NI
l
Describes, so to speak, a linear connection between B and H or between B and
I. This is not so. When the coil core is not magnetized and we gradually raise
H (by increasing the current in the bindings), the magnetic flaw density will
grow as follows:
B
H
Figure 1-9
At first B will increase in a relatively large slope and afterwards the slope will
change to a very moderate slope.
The reason for that is that at the beginning the influence of H on the core
magnetism is great, but at a certain situation the core reaches a maximum
magnetism and does not grow anymore. The core reaches a saturation state.
If we will decrease H gradually now, B will not decrease by the characteristic
described in the figure. When H equals 0 (I equals 0), there will be magnetic
flaw in the core because the current stays magnetized. To reset the magnetic
flaw H should get negative (reversed current)
EB-3124 – Magnetism, Induction and Transformers
10
The magnetic flaw characteristic depending on H of the coil with a
Ferromagnetic core looks like this:
B
c
h
b
d
i
Br
f
a
j
0
e
m
g
H
Hc
l
k
Figure 1-10
1.7
Electromagnet
A coil which current flows through it becomes a magnet. Adding a core of
Ferromagnetic matter (usually iron) strengthen considerably the magnetic
field. Stopping the current weakens the magnetic field and leaves the magnetic
residue in the core.
This kind of coil with a core is called electromagnet. It is a magnet operated
by electric current. Because we want the magnetization to stop when the
current stops, we use a soft iron core with a small magnetic residue.
Electromagnet is used to lift cargos. There are electromagnets that can lift
hundreds of Kilograms.
EB-3124 – Magnetism, Induction and Transformers
11
1.8
The relay
The electromagnet can be found in every electro-mechanic relay. The relay is
a system where the electromagnet closes two electric contacts when current
flows in its coil.
C
D
A
B
Figure 1-11
Sending current between A and B causes the electromagnet to operate and the
switch connected to points C and D to close.
The influence of the electromagnet is limited in range (millimeters to
centimeters only)
1.9
Solenoid
The concept solenoid means a coil where the core inside is moving. When we
put a soft iron rod inside a coil and send current through the coil, the core will
magnetize. If it can move, it will move until it will be in equal distance from
the two sides of the coil.
The solenoid is used as a lever for operating valves, taps and opening locks
electrically. In the regular state of the solenoid, the spring pulls the core
outside.
Figure 1-12
EB-3124 – Magnetism, Induction and Transformers
12
1.10
PWM signal
There are two ways to regulate power in a consumer. One is an analog way by
changing the consumer's voltage.
The second way is to supply the consumer digital pulses and controlling the
width of these pulses. The ON duration of the pulses dictates the intensity of
the power to the consumer.
The consumer reacts to the average voltage of the signal.
The following drawing describes two PWM signals with different average
voltages.
Average
Voltage
Average
Voltage
Figure 1-13
EB-3124 – Magnetism, Induction and Transformers
13
Preparation questions:
1.
Where the magnetic force will be higher – in a coil with an iron core or in
a coil without an iron core?
(a)
(b)
(c)
(d)
2.
The magnetic force will be higher in a coil with an iron core.
The magnetic force will be higher in a coil without an iron core.
The magnetic force will be the same in both cases.
It depends on the coil wire thickness.
Two signals were supplied to an electromagnet.
Signal A
Signal B
Which of them creates a higher magnetic force?
(a)
(b)
(c)
(d)
Signal A creates a higher magnetic force.
Signal B creates a higher magnetic force.
Both signals create the same magnetic force.
It depends on the voltage.
EB-3124 – Magnetism, Induction and Transformers
14
3.
What will happen when the pushbutton is pressed?
+12V
12V
(a)
(b)
(c)
(d)
Nothing will happen.
The electromagnet is turned OFF.
The electromagnet is turned ON.
The relay is ON and the electromagnet is OFF.
EB-3124 – Magnetism, Induction and Transformers
15
Procedure:
Step 1:
Connect the EB-3100 to the power supply.
Step 2:
Connect the power supply to the Mains.
Step 3:
Turn ON the trainer. The DVM screen should appear on the display.
Step 4:
Plug the EB-3124 into the EB-3100.
Step 5:
Observe the display and check that the experiment board name
appear and no fault is detected.
The EB-3124 includes the power supply outlets +12V.
It also includes a digital PWM signal generator and an AC 50/60Hz
power supply.
Step 6:
Hang a paper clip on the sewing thread 2cm before the transformer
without the core. This paper clip will function as a pendulum and
will allow us to observe the electromagnet power created.
Step 7:
Connect the transformer B (without the core) primary coil to 12V.
+12V
GND
Step 8:
Press the pushbutton.
The paper clip should move towards the transformer.
EB-3124 – Magnetism, Induction and Transformers
16
Step 9:
Release the pushbutton.
The paper clip should go back to its original place.
Step 10: Connect the voltage in the opposite direction.
Again, the paper clip should move towards the transformer. Why?
Step 11: Return the voltage to the previous direction.
Step 12: Insert paper clips to the space inside the transformer.
As more paper clips will be added, the electromagnetic power will
grow and the hanged paper clip will move closer to the transformer.
Step 13: After filling the transformer with paper clips, check the angle
created between the hanged paper clip and the transformer core.
This is a type of an electromagnet.
Step 14: Disconnect the transformer from the voltage source.
Is the paper clip came loose completely or stayed at a certain angel
to the transformer?
It is reasonable to assume that the paper clip stayed at a certain
angle because of the magnetic residue at the core.
Step 15: Reverse the voltage direction in the transformer.
Is the paper clip was rejected or was drawn again to the
transformer?
Explain why?
Step 16: Pull out the paper clips from the core.
Step 17: Put one paper clip in the hole, but take care to let most of it hang
out.
EB-3124 – Magnetism, Induction and Transformers
17
Step 18: Press the pushbutton.
The paper clip will jump into the core.
This is a type of a solenoid.
Step 19: Repeat steps 17 and 18 in different ways and from different
directions.
Step 20: Connect the primary coil of the transformer A with the core to
points +12V and GND.
Step 21: Bring the paper clip closer to the transformer core.
Is the paper clip cling to it?
Is the core function as an electromagnet?
Probably not.
Explain why.
Real electromagnet:
Step 22: Implement the following circuit using the board electromagnet in
B3.
+12V
Electromagnet
Step 23: Bring the hanged paper clip near the electromagnet.
EB-3124 – Magnetism, Induction and Transformers
18
Step 24: Press the switch and observe the paper clip moving.
The angle of the paper clip thread represents the intensity of the
electromagnet pull.
The FET circuit is used as a driver circuit for the electromagnet.
Step 25: Release the pushbutton switch and observe the paper clip moving
back.
Step 26: We can control the electromagnet intensity using the PWM signal.
We must also use the FET driver in B2.
Implement the following circuit:
+12V
CH1
PWM
Signal
R2
10K
Electromagnet
R1
1M
Step 27: Connect the PWM signal generator output to the scope probe CH1.
Step 28: Change the PWM generator potentiometer and observe the effect on
the electromagnet intensity.
EB-3124 – Magnetism, Induction and Transformers
19
A relay:
Step 29: The relay is an electromagnet that manipulates a changeover switch,
like the one on the EB-3124.
Implement the following circuit:
+12V
+12V
Electromagnet
Relay
Step 30: Pressing the pushbutton switch will operate the relay (you should
hear a click) and will close the electromagnet circuit with the 12V
power supply.
Press the pushbutton and check the relay and the electromagnet
behavior.
Step 31: Release the hanged paper clip.
Real solenoid:
Step 32: Implement the following circuit:
+12V
Solenoid
EB-3124 – Magnetism, Induction and Transformers
20
Step 33: The solenoid contains an internal rod with a spring.
Press the pushbutton switch.
The rod should enter into the solenoid.
Step 34: Release the pushbutton and the rod should exit the solenoid because
of the spring.
EB-3124 – Magnetism, Induction and Transformers
21
Summary questions:
1.
Where the magnetic force will be higher – in a coil with an iron core or in
a coil without an iron core?
(a)
(b)
(c)
(d)
2.
The magnetic force will be the same in both cases.
It depends on the coil wire thickness.
The magnetic force will be higher in a coil with an iron core.
The magnetic force will be higher in a coil without an iron core.
Two signals were supplied to an electromagnet.
Signal A
Signal B
Which of them creates a higher magnetic force?
(a)
(b)
(c)
(d)
Signal A creates a higher magnetic force.
Both signals create the same magnetic force.
It depends on the voltage.
Signal B creates a higher magnetic force.
EB-3124 – Magnetism, Induction and Transformers
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3.
What will happen when the pushbutton is pressed?
+12V
+12V
Electromagnet
Relay
(a)
(b)
(c)
(d)
The relay is ON and the electromagnet is OFF.
The electromagnet is turned ON.
The electromagnet is turned OFF.
Nothing will happen.
EB-3124 – Magnetism, Induction and Transformers
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Experiment 2 – The Transformer
Objectives:
 Introducing the transformer.
 The transformer's core function.
 Transformer in direct current and alternate current.
Equipment Required:
 EB-3100
 EB-3124
 Banana wires
Discussion:
2.1
Induced drive electro power
As we saw, electric current in a bind or a coil causes a magnetic field inside
the bind or the coil.
It seems that if somehow the magnetic flaw is changed in the bind, an electric
voltage will be induced between the bind terminals. The electric voltage is a
function of the change speed. This voltage is called induced drive electro
power.
If we mark the magnetic flaw with the letter , then the induced Drive Electro
Power (D.E.P) E is:
E

t
In a coil with N binds we will get the following induced D.E.P:
EN

t
EB-3124 – Magnetism, Induction and Transformers
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If the bind or coil is closed in an electric circuit, current will flow through
them according to the induced D.E.P. This current is called induced current.
Lenz law:
Lenz determined a useful rule for determining the direction of the induced
current:
"An induced current is always in such a direction as to oppose the motion or
change causing it".
Thus, if the magnetic flow is small, a voltage will be induced, which will try
to send current through the bind to increase the magnetic flow, and vice versa.
If we bring a magnet closer to an electric coil or pass a magnet by an electric
coil, D.E.P will be induced at the coil's triggers as described in the following
drawing:
N S
Figure 2-1
The induced D.E.P direction is according to the binds direction and Lenz law.
EB-3124 – Magnetism, Induction and Transformers
25
2.2
The transformer
We can change the magnetic flow in another way. We take two coils, arranged
thus that the magnetic flow created in one coil passes through the second coil
as well. If we change the current in one coil it will cause a flow change in the
two coils and the appearance of induced D.E.P in the second coil. This system
is called a transformer.
You can wrap a coil on top a coil and you can use a closed core to transfer the
magnetic flow from coil to coil.
Figure 2-2
The EB-3124 includes two identical transformers with one distinction: one
transformer with a core and one without. We will use the transformer without
the core to demonstrate electromagnetic phenomenon.
The transformers are bound as follows:
Figure 6-15
EB-3124 – Magnetism, Induction and Transformers
26
Preparation questions:
In the following transformer:
A
AC Power Supply
B
C
D
E
NAB = 1000
NCD = 250
NDE = 250
1.
If VAB = 6V, what will be the value of VCD?
(a)
(b)
(c)
(d)
2.
If VAB = 6V, what will be the value of VCE?
(a)
(b)
(c)
(d)
3.
6V
3V
12V
1.5V
6V
3V
12V
1.5V
If VCD = 3V, what will be the value of VAB?
(a)
(b)
(c)
(d)
6V
3V
12V
1.5V
EB-3124 – Magnetism, Induction and Transformers
27
Procedure:
Step 1:
Connect the EB-3100 to the power supply.
Step 2:
Connect the power supply to the Mains.
Step 3:
Turn ON the trainer. The DVM screen should appear on the display.
Step 4:
Plug the EB-3124 into the EB-3100.
Step 5:
Observe the display and check that the experiment board name
appear and no fault is detected.
The EB-3124 includes the power supply outlets +12V.
It also includes a digital PWM signal generator and an AC 50/60Hz
power supply.
Step 6:
Connect the 12V direct current to the primary coil of the transformer
A with the core.
+12V
A
C
D
B
E
GND
Step 7:
Measure the voltage at the secondary coils (CD, DE, CE).
The voltage should be 0V.
Transformer does not pass direct voltage.
EB-3124 – Magnetism, Induction and Transformers
28
Step 8:
Connect the transformer primary coil A to the AC power supply
output in the trainer (TP3).
A
AC Power Supply
B
Step 9:
C
D
E
Connect point A to CH1 and point C to CH2.
Step 10: Connect points B and E to GND.
Step 11: Measure the alternate voltage between the inputs AB.
Write it down as VAB.
Step 12: Measure the alternate voltage between the inputs CE.
Write it down as VCE.
Step 13: Calculate the coiling ratio between AB and CE.
n AB/CE 
VAB
VCE
Step 14: Connect point D to GND.
Step 15: Measure the voltage VCD between the outputs CD.
Step 16: Calculate the coiling ratio between AB and CD.
n AB/CD 
VAB
VCD
Step 17: Connect point D to CH2 and point E to GND.
Step 18: Measure the voltage VDE between the outputs DE.
EB-3124 – Magnetism, Induction and Transformers
29
Step 19: Calculate the coiling ratio between AB and DE.
n AB/DE 
VAB
VDE
Step 20: Check if:
VC E  VC D  VDE
Step 21: Connect the AC power supply to the secondary coil CD.
Step 22: Measure the voltage received at the AB primary coil's triggers.
Step 23: Check in the ratio between VCD and VAB is maintained.
VAB  n AB/DC  VCD
Step 24: Connect the AC power supply to the secondary coil DE.
Step 25: Measure the voltage received at the AB primary coil's triggers.
Step 26: Check in the ratio between VDE and VAB is maintained.
VAB  n AB/DE  VDE
Step 27: Connect the AC power supply to the primary coil of the transformer
B without the core.
A
AC Power Supply
B
C
D
E
Step 28: Measure the voltages in the secondary coils CE, DC, and DE.
Step 29: Compare the values you've got with the transformer without the core
and the values you've got with the transformer with the core.
Although they have the same coils, the values are much lower.
EB-3124 – Magnetism, Induction and Transformers
30
Summary questions:
In the following transformer:
A
AC Power Supply
B
C
D
E
NAB = 1000
NCD = 250
NDE = 250
1.
If VAB = 6V, what will be the value of VCD?
(a)
(b)
(c)
(d)
2.
If VAB = 6V, what will be the value of VCE?
(a)
(b)
(c)
(d)
3.
1.5V
12V
6V
3V
1.5V
12V
6V
3V
If VCD = 3V, what will be the value of VAB?
(a)
(b)
(c)
(d)
1.5V
12V
6V
3V
EB-3124 – Magnetism, Induction and Transformers
31
Experiment 3 – Troubleshooting
Objectives:
 Troubleshooting faults in an electrical circuit.
Equipment required:
 EB-3100
 EB-3124
 Banana wires
Discussion:
The EB-3100 includes 10 relays for fault insertion or for switching external
components.
The fault screen is selected by the Options/Graph key.
FAULTS
Please choose
Fault No.: 0–9
Activated fault
Number: 0
Num Lock
Typing a fault number and pressing ENTER operates the required relay for the
required fault.
Fault No. 0 means No Fault.
Which relay creates the required fault is registered in the plug-in experiment
board controller.
On entering a fault number, the system addresses the experiment board
controller and asks for the relay number. After that, it executes the required
fault.
EB-3124 – Magnetism, Induction and Transformers
32
The experiment board controller saves the last registered fault number in its
memory. This memory is non-volatile.
This is why the system does not allow us to enter a fault number when no
experiment board is plugged.
When an experiment board that a certain fault (other than zero) is registered in
its memory is plugged into the system, a warning message appears on the
system's screen.
This feature enables the teacher to supply the students various experiment
boards with planted faults for troubleshooting.
Note:
It is recommended (unless it is otherwise required), to return the
experiment board fault number to zero before unplugging it.
EB-3124 – Magnetism, Induction and Transformers
33
Procedure:
Step 1:
Connect the EB-3100 to the power supply.
Step 2:
Connect the power supply to the Mains.
Step 3:
Turn ON the trainer. The DVM screen should appear on the display.
Step 4:
Plug the EB-3124 into the EB-3100.
Fault No. 1:
Step 5:
Use the B1 and B4 components and implement the following
circuit.
A
AC Power Supply
B
Step 6:
C
D
E
Enter fault no. 1.
What is the fault?
(a)
(b)
(c)
(d)
Coil AB is disconnected.
Coil DC is disconnected.
Coil DE is disconnected.
There is no voltage source.
EB-3124 – Magnetism, Induction and Transformers
34
Fault No. 2:
Step 7:
Use the B1 and B4 components and implement the following
circuit.
+12V
CH1
Electromagnet
PWM
Signal
Step 8:
Enter fault no. 2.
What is the fault?
(a)
(b)
(c)
(d)
The D leg of the transistor is disconnected.
The D leg of the transistor is short-circuited to GND.
The S leg of the transistor is disconnected.
There is no voltage source.
EB-3124 – Magnetism, Induction and Transformers
35
Fault No. 3:
Step 9:
Use the B1 and B4 components and implement the following
circuit.
+12V
CH1
Electromagnet
PWM
Signal
Step 10: Enter fault no. 3.
What is the fault?
(a)
(b)
(c)
(d)
The D leg of the transistor is disconnected.
The D leg of the transistor is short-circuited to GND.
The S leg of the transistor is disconnected.
There is no voltage source.
EB-3124 – Magnetism, Induction and Transformers
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Fault No. 4:
Step 11: Use the B2 and B3 components and implement the following
circuit.
+12V
+12V
Electromagnet
Relay
Step 12: Enter fault no. 4.
What is the fault?
(a) The relay coil is disconnected.
(b) The common terminal of the relay switch is disconnected.
(c) The Normally Open terminal of the relay switch is
disconnected.
(d) There is no voltage source.
EB-3124 – Magnetism, Induction and Transformers
37
Fault No. 5:
Step 13: Use the B2 and B3 components and implement the following
circuit.
+12V
+12V
Electromagnet
Relay
Step 14: Enter fault no. 5.
What is the fault?
(a) The relay coil is disconnected.
(b) The common terminal of the relay switch is disconnected.
(c) The Normally Open terminal of the relay switch is
disconnected.
(d) There is no voltage source.
EB-3124 – Magnetism, Induction and Transformers
38
Fault No. 6:
Step 15: Use the B2 and B3 components and implement the following
circuit.
+12V
+12V
Electromagnet
Relay
Step 16: Enter fault no. 6.
What is the fault?
(a) The relay coil is disconnected.
(b) The common terminal of the relay switch is disconnected.
(c) The Normally Open terminal of the relay switch is
disconnected.
(d) There is no voltage source.
EB-3124 – Magnetism, Induction and Transformers
39
Fault No. 7:
Step 17: Implement the following circuit using the B2 and B3 components.
+12V
Electromagnet
Step 18: Enter fault no. 7.
What is the fault?
(a)
(b)
(c)
(d)
The pushbutton switch is disconnected.
The electromagent is short-circuited to GND.
The electromagnet coil is disconnected.
There is no voltage source.
EB-3124 – Magnetism, Induction and Transformers
40
Fault No. 8:
Step 19: Use the B1 and B4 components and implement the following
circuit.
A
AC Power Supply
B
C
D
E
Step 20: Enter fault no. 8.
What is the fault?
(a)
(b)
(c)
(d)
Coil AB is disconnected.
Coil DC is disconnected.
Coil DE is disconnected.
There is no voltage source.
EB-3124 – Magnetism, Induction and Transformers