View
6
Download
0
Category
Preview:
Citation preview
Capacitor Transients – Simulator Applet Updated 20 JUN 2019
A Practical Exercise Name:________________ Section: ____________
I. Purpose.
1. Review the operation of the oscilloscope.
2. Review the measurement of DC voltages using an oscilloscope.
3. Introduce the capture and display of an electrical signal with the oscilloscope.
4. Introduce the variation of voltage across a capacitor during charging and discharging.
II. Equipment.
Agilent E3620A Dual DC Power Supply
Oscilloscope
Relay and Trigger Box, Ink Pen, 12ft of 24 AWG wire, 15000-μF capacitor w/ discharge resistor
47Ω resistor
Safety Glasses
Circuit Simulator Applet
An introduction to the Circuit Simulator Applet
III. Pre-lab calculations. Show all work.
Step One: Determine the expected steady-state voltage VC across the capacitor in the circuit of Figure 1
when the switch is in position a (charging circuit is BOLD). Remember that capacitors act like an open
circuit under steady-state DC conditions.
DC DC
V124 V
V212 V
2 kΩ DischargeResistor
Coil Resistance0.3 Ω
+ -15,000 µF
PushbuttonTrigger
Relay Switch
47 ΩCurrent Limiting Resistor
b a
VC = _____
Figure 1
Capacitor Transients
2 of 17
Step Two: Charging Transient
□ Determine the equation for the voltage across the capacitor while it is charging. Assume the
capacitor is initially discharged with the pushbutton trigger pressed closed. The transient will begin
when the pushbutton trigger is released and the relay switch moves to position a.
Hint: this is not the simple circuit first discussed in the lecture. You must find the Thèvenin equivalent
of the circuit, treating the capacitor as the load. The Thèvenin resistance will be used in calculating the
time constant.
vC (t)= __________________________
□ How long do you predict the charging transient will last?
t = ______________
□ Sketch the voltage across the capacitor during the charging transient. Label the axis for peak voltage
and time.
Capacitor Transients
3 of 17
Step Three: Firing Transient
□ Determine the equation for the voltage across the capacitor while the coil gun is firing. Assume the
capacitor is initially fully charged with the switch in position a. The transient begins when the
trigger is pressed and the relay switches to position b (discharging circuit is BOLD). The inductance
of the coil is negligible when determining the discharge transient of this circuit. The coil can be
treated as a simple resistor of 0.3 ohms.
DC DC
V124 V
V212 V
2 kΩ DischargeResistor
Coil Resistance0.3 Ω
+ -15,000 µF
PushbuttonTrigger
Relay Switch
47 ΩCurrent Limiting Resistor
ab
vC (t)= __________________________
□ How long do you predict the discharge transient will last?
t = ______________
□ Sketch the voltage across the capacitor during the discharge transient. Label the axis for peak
voltage and time.
Capacitor Transients
4 of 17
Step Four: Discharge Transient
□ Determine the equation for the voltage across the capacitor while it is discharging. Assume the
capacitor is initially fully charged with the pushbutton trigger switch open. The transient begins
when the power source is turned off. Hint: when the power supply is turned off, it acts as an open
circuit.
DC DC
V124 V
V212 V
2 kΩ DischargeResistor
Coil Resistance0.3 Ω
+ -15,000 µF
PushbuttonTrigger
Relay Switch
47 ΩCurrent Limiting Resistor
ab
vC (t)= __________________________
□ How long do you predict the discharge transient will last?
t = ______________
□ Sketch the voltage across the capacitor during the discharge transient. Label the axis for peak
voltage and time.
Step Five: Instructor verification that pre-lab calculations are complete.
_____________________
Capacitor Transients
5 of 17
IV. Lab Procedure. Time required: 60 minutes. Check-off each step as you complete it.
WARNINGS:
1. SAFETY GLASSES MUST BE WORN AT ALL TIMES. Violation will result in a 0 lab
grade for the term.
2. CAPACITORS HAVE DANGEROUS AMOUNTS OF ENERGY. FOLLOW ALL
PROCEDURES EXACTLY AND VERIFY ZERO VOLTAGE BEFORE TOUCHING.
Step One – INSTRUCTOR DEMONSTARION:
□ Ensure V1 and V2 of the power supply are both set to 0V. Turn off power supply.***
□ Wrap the ink pen barrel with the 24 AWG wire provided to construct your coil gun. You may add as
many layers of wire coils as you desire, but you must leave 1ft of wire on each end to plug into the
firing circuit. For best results, ensure the current is flowing the same direction in all the coils (i.e.
clockwise or counter clockwise) and that the coil begins directly in front of the loaded projectile as
shown below.
Capacitor Transients
6 of 17
□ On your QUAD board, construct the coil gun circuit using Figures 3 and 4 below. Ensure that the
capacitor’s polarity is correct
***DO NOT TURN ON POWER SUPPLY UNTIL YOUR CIRCUIT HAS BEEN CHECKED.
DC DC
V1 V2
2 kΩ
+ -15,000 µF
1Trigger
A
4
7
Trigger and Relay Box
47 Ω
Figure 2
4
7
1
A
Figure 3
DMM
Volts
Capacitor Transients
7 of 17
Step Two – INSTRUCTOR DEMONSTARION: Test fire coil gun
□ 24V Test Fire: Set V1 to 24V and V2 to 0V. Verify that the DMM reads ~ 24V. For safety, the
DMM provides constant monitoring of the capacitor voltage. DO NOT TOUCH THE
CAPACITOR WHILE THE DMM READS MORE THAN 500 mV.
□ With the projectile loaded and coil gun aimed in a safe direction, press the trigger to fire the
projectile. The projectile should only travel a few inches. If not, adjust the coil position by
sliding it up and down the pen until you get a successful launch.
□ 36V Test Fire: Set V1 to 24V and V2 to 12V. Verify that the DMM reads ~ 36V.
□ With the projectile loaded and coil gun aimed in a safe direction, press the trigger to fire the
projectile. The projectile should travel a few feet. If needed, adjust the coil position for best
performance.
□ 48V Test Fire: Set V1 to 24V and V2 to 24V. Verify that the DMM reads ~48V.
□ With the projectile loaded and coil gun aimed in a safe direction, press the trigger to fire the
projectile.
□ The equation for energy stored in a capacitor is below and is proportional to voltage squared.
Therefore, you should have observed an exponential increase of velocity and distance as the
voltage was increased.
Step three: Create Circuit in Simulation Applet
□ Build the following circuit. NOTE: The inductor is being modeled by a 0.3 Ohm resistor.
21
2CW Cv
24 VDC Source 12 VDC Source
Push Switch Relay Polarized 15000 µF Capacitor
0.3 Ohm Resistor When constructing the circuit,
PAY ATTENTION TO THE
NODES (where connections
occur). The nodes are
annotated by the white dot.
Just because a wire crosses
does not mean it’s connected.
Connections only occur at the
nodes.
Capacitor Transients
8 of 17
Step Four: Capture a capacitor discharging while firing
□ Select “View in Scope” for the Polarized Capacitor
□ RUN simulation until the capacitor voltage reaches the steady state voltage calculated in step 1 of
the pre-lab.
□ In the Scope Properties, set the Scroll Speed to 2ms/div and set the Simulation Speed to about 2/3
red.
□ Click and hold the Push Button until the Capacitor has discharged for half the scope (about 2-3 sec)
and in RAPID succession STOP the simulation.
NOTE: If you do hold the Push button long enough or do not STOP the simulation quick enough and
need to recharge the capacitor to try again, you can charge the capacitor more quickly by changing the
Scroll Speed to 200ms/div and the Simulation Speed to fully red. Remember to reset the settings before
discharging the Capacitor.
□ Sketch the picture on the scope for the capacitor transient on Figure 4. (Hint: It should look similar
to the Firing Transient of the pre-lab.) Label the voltage at the start of the firing transient.
Capacitor Transients
9 of 17
Time: _____ s/div
Figure 4
□ Count the divisions between the voltage when it is fully charged and when the capacitor reaches
fully discharged. NOTE: The fully discharged voltage is not 0V, but can be calculated using 5τ and
the vC (t) equation in Step Three of the pre-lab.
How much time did the capacitor take to fully discharge? _______________
How does the charge time compare to the values calculated in step 3 of the pre-lab?
Exact__________ Very close__________ Very Different_________
Step Five: Capture the capacitor recharging after firing
□ In the Scope Properties, set the Scroll Speed to 200ms/div and set the Simulation Speed to fully red.
Capacitor Transients
10 of 17
□ Run the Simulation until the Capacitor has fully charged (about 30 - 35 sec) and in RAPID
succession STOP the simulation.
□ Sketch the picture on the scope for the capacitor transient on Figure 5. (Hint: It should look similar
to the Charging Transient of the pre-lab.) Label the voltage at the end of the firing transient.
Time: _____ s/div
Figure 5
□ Count the divisions between the voltage when it is fully discharged and when the capacitor reaches
fully charged. NOTE: The fully charged voltage is not 35.17 V, but can be calculated using 5τ and
the vC (t) equation in Step Two of the pre-lab.
How much time did the capacitor take to fully charge? _______________
How does the charge time compare to the values calculated in step 2 of the pre-lab?
Exact__________ Very close__________ Very Different_________
1
Capacitor Transients
11 of 17
Step Six: Analyze your results
□ Run the Simulation and allow the capacitor to continue charging for 1 minute.
What is Maximum voltage that your capacitor charged to: ________________
How does this voltage compare to the value of VC calculated in step 1 of the pre-lab?
Exact__________ Very close__________ Very Different_________
What is the minimum voltage that your capacitor discharged to? _______________
When the capacitor reached its maximum voltage, how much current should be flowing through the
capacitor? _______________________________________________________________________
When the capacitor reached its maximum voltage, how much energy is stored in the capacitor?
WC =______________
Step Seven: Circuit Submission
□ Save the circuit to your computer and submit the circuit text file to your instructor for lab credit.
21
2CW Cv
Capacitor Transients
12 of 17
Practical Exercise Submission Form Name:________________ Section: _____
III. Pre-lab calculations. Show all work.
Step One: Determine the expected steady-state voltage VC across the capacitor in the circuit of Figure 1
when the switch is in position a (charging circuit is BOLD). Remember that capacitors act like an open
circuit under steady-state DC conditions.
DC DC
V124 V
V212 V
2 kΩ DischargeResistor
Coil Resistance0.3 Ω
+ -15,000 µF
PushbuttonTrigger
Relay Switch
47 ΩCurrent Limiting Resistor
b a
VC = _____
Figure 1
Capacitor Transients
13 of 17
Step Two: Charging Transient
□ Determine the equation for the voltage across the capacitor while it is charging. Assume the
capacitor is initially discharged with the pushbutton trigger pressed closed. The transient will begin
when the pushbutton trigger is released and the relay switch moves to position a.
Hint: this is not the simple circuit first discussed in the lecture. You must find the Thèvenin equivalent
of the circuit, treating the capacitor as the load. The Thèvenin resistance will be used in calculating the
time constant.
vC (t)= __________________________
□ How long do you predict the charging transient will last?
t = ______________
□ Sketch the voltage across the capacitor during the charging transient. Label the axis for peak voltage
and time.
Capacitor Transients
14 of 17
Step Three: Firing Transient
□ Determine the equation for the voltage across the capacitor while the coil gun is firing. Assume the
capacitor is initially fully charged with the switch in position a. The transient begins when the
trigger is pressed and the relay switches to position b (discharging circuit is BOLD). The inductance
of the coil is negligible when determining the discharge transient of this circuit. The coil can be
treated as a simple resistor of 0.3 ohms.
DC DC
V124 V
V212 V
2 kΩ DischargeResistor
Coil Resistance0.3 Ω
+ -15,000 µF
PushbuttonTrigger
Relay Switch
47 ΩCurrent Limiting Resistor
ab
vC (t)= __________________________
□ How long do you predict the discharge transient will last?
t = ______________
□ Sketch the voltage across the capacitor during the discharge transient. Label the axis for peak
voltage and time.
Capacitor Transients
15 of 17
Step Four: Discharge Transient
□ Determine the equation for the voltage across the capacitor while it is discharging. Assume the
capacitor is initially fully charged with the pushbutton trigger switch open. The transient begins
when the power source is turned off. Hint: when the power supply is turned off, it acts as an open
circuit.
DC DC
V124 V
V212 V
2 kΩ DischargeResistor
Coil Resistance0.3 Ω
+ -15,000 µF
PushbuttonTrigger
Relay Switch
47 ΩCurrent Limiting Resistor
ab
vC (t)= __________________________
□ How long do you predict the discharge transient will last?
t = ______________
□ Sketch the voltage across the capacitor during the discharge transient. Label the axis for peak
voltage and time.
Step Five: Instructor verification that pre-lab calculations are complete.
_____________________
Capacitor Transients
16 of 17
IV. Lab Procedure.
Step Four: Capture a capacitor discharging while firing
□ Sketch the picture on the scope for the capacitor transient on Figure 4. (Hint: It should look similar
to the Firing Transient of the pre-lab.) Label the voltage at the start of the firing transient.
Time: _____ s/div
Figure 4
□ Count the divisions between the voltage when it is fully charged and when the capacitor reaches
fully discharged. NOTE: The fully discharged voltage is not 0V, but can be calculated using 5τ and
the vC (t) equation in Step Three of the pre-lab.
How much time did the capacitor take to fully discharge? _______________
How does the charge time compare to the values calculated in step 3 of the pre-lab?
Exact__________ Very close__________ Very Different_________
Step Five: Capture the capacitor recharging after firing
□ Sketch the picture on the scope for the capacitor transient on Figure 5. (Hint: It should look similar
to the Charging Transient of the pre-lab.) Label the voltage at the end of the firing transient.
Time: _____ s/div
Figure 5
1
1
Capacitor Transients
17 of 17
□ Count the divisions between the voltage when it is fully discharged and when the capacitor reaches
fully charged. NOTE: The fully charged voltage is not 35.17 V, but can be calculated using 5τ and
the vC (t) equation in Step Two of the pre-lab.
How much time did the capacitor take to fully charge? _______________
How does the charge time compare to the values calculated in step 2 of the pre-lab?
Exact__________ Very close__________ Very Different_________
Step Six: Analyze your results
What is Maximum voltage that your capacitor charged to: ________________
How does this voltage compare to the value of VC calculated in step 1 of the pre-lab?
Exact__________ Very close__________ Very Different_________
What is the minimum voltage that your capacitor discharged to? _______________
When the capacitor reached its maximum voltage, how much current should be flowing through the
capacitor? _______________________________________________________________________
When the capacitor reached its maximum voltage, how much energy is stored in the capacitor?
WC =______________
Step Seven: Circuit Submission
□ Save the circuit to your computer and submit the circuit text file to your instructor for lab credit.
21
2CW Cv
Recommended