Introduction to Engineering
Camera Lab #4
Procedure
1.1
Introduction
In Lab 4 you perform measurements on various parts of the camera flash
circuit while each of the core functions is being executed. You will be using a
digital multimeter and an oscilloscope to measure voltages. The digital
multimeter will allow you to measure steady DC voltages and monitor voltages
that are slowly changing with time. With the oscilloscope you will be able to
display time histories of voltages that are changing rapidly with time.
In many cases we would like to know currents flowing in the circuit,
however, it is difficult to measure currents directly. To directly measure current
we would have to break the circuit and insert the measuring instrument in series
with the component whose current we wish to measure. That would require us to
unsolder one end of the component from the circuit board and clip or solder the
current meter between that end of the component and the point on the circuit
board to which it was originally attached. That is not practical in many cases,
and the limited time for Lab 4 does not allow us to do that. In addition, while the
digital multimeter has a current measuring capability, the oscilloscope is not
designed to measure currents.
To extract information about currents flowing in the circuit you will
therefore need to use voltage measurements along with the equations presented
in this document.
In addition to the digital multimeter and oscilloscope, you will be using a
test box that will simplify some of your connections. These connections are
called ‘test points’ and are labeled on the test box.
Warning: To minimize the chance of accidentally contacting high voltage,
only one team member at a time should be handling the test box
or connecting wires. We suggest that while one member of a
team is making the connections the others carefully watch to
make sure that the correct connections are made in a safe
manner. AN ELECTRICAL SHOCK CAN OCCUR IF ANY TWO
PARTS OF A PERSON’S BODY CONTACT ANY TWO
BINDING POSTS AT THE SAME TIME.
Warning: Always connect the test leads to the measuring instrument first.
Then connect to the appropriate test point on the test box.
Handle the test leads by holding only the insulated portions.
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Procedure 08/07/02 mjh
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1.2
Preliminary Tasks
Insure you have the following items available at your work table:
o
o
o
o
o
a two-channel oscilloscope (scope) with two test probes,
a test box,
a digital multimeter (DMM),
a stopwatch or your wristwatch with seconds reading, and,
a set of two wires with banana plugs at each end.
Now, plug the power cord from the scope into a wall outlet, and push the
power button, located below the lower right corner of the display screen, to
the ‘ON’ position. Press the ‘Save/Recall’ button, then press the ‘Default
Setup’ softkey. Now press the ‘Run/Stop’ button and that button’s color
should turn from green to red.
Connect the test probes to the scope as shown below. The connectors are
called BNC type and they must be slid onto the scope mating connector and
given a quarter-twist clockwise to fasten. A quarter-twist counter-clockwise
will release the connector. Note the alignment pin on the scope portion of
the connector, and the swiveling action of the test probe connector. To
properly connect the test probes, always hold the connector by the portion
with grooves in it and always line up the alignment pins with the ‘slots’. This
method will allow easier connection and disconnection.
SOFT KEYS
OSCILLOSCOPE
(scope)
POWER Push ON
Push OFF
TEST PROBES
CH 1
CH 2
DIGITAL
MULTIMETER
(DMM)
A DMM is shown above. Remove the test leads from the DMM at your table and
attach the banana plug leads to the DMM with the BLACK LEAD plugged into the
‘COM’ hole and the RED LEAD plugged into the ‘VmA’ hole. Turn the large
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knob on the DMM ‘one click’ counter-clockwise from the OFF position. This
action will put the DMM on a 600 volt DC scale.
The test box is shown below.
Note the location of the various test points
(binding posts labeled ‘TP x’ below). Reference to the test points is made
throughout the rest of the procedure. The easiest way to use the test points is to
carefully unscrew the outer plastic ‘nuts’ until a small hole through the center post
is viewable. The test probes can clip to each respective post with the help of that
hole. Note also the location of the POWER switch and the CHARGE and FLASH
buttons.
CAPACITOR (TP 1)
INDICATOR
LIGHT (TP 2)
FLASH
TRIGGER (TP 3)
POWER
CHARGE
1.3
FLASH
CAPACITOR (TP 4)
CAPACITOR +
(TP 5, TP 6)
Task 1 - Transient Measurement: Capacitor Charging Function
1. Insure the test box POWER switch is in the OFF position. IF YOU ARE
EVER IN DOUBT ABOUT THE ELECTRICAL STATUS OF THE TEST
BOX, FLIP THE POWER SWITCH TO ‘OFF’ AND ASK FOR HELP !!!
2. Connect the BLACK LEAD of the DMM to the test box TP 4
‘CAPACITOR–‘ RED POST (positioned towards the bottom of the of test
box panel). Connect the RED LEAD of the DMM to the test box TP 5
‘CAPACITOR +’ BLACK POST.
3. Connect Channel 1 (CH 1) test probe of the oscilloscope to the TP 6
‘CAPACITOR +’ test point. Connect the small black alligator clip of the
CH 1 test probe to the TP 1 ‘CAPACITOR –‘ test point. Connect Channel
2 (CH 2) test probe to the TP 2 ‘INDICATOR LIGHT’ test point. The small
black alligator clip of the CH 2 test probe is not used.
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4. Both scope CH 1 and CH 2 must be ‘ON’, as indicated by channel select
buttons’ lights being lit to green. Press CH 2 button to turn on CH 2. (CH
1 should already be on). The reference position for each channel should
be set to one division above the bottom of the display (use the small knob
below the channel select button to adjust the reference position).
5. Now the scope must be set up to record the voltages from the two test
points (the capacitor voltage and the indicator light voltage). Both scope
channels can be set to the same vertical scale of 50 volts/div. Use the
large knob above each channel select button in the Vertical control section
to set the respective vertical scale. Read the respective value in the
upper left corner of the display. That reading should show ’50.0V/’ when
properly adjusted. The horizontal scale (time base) must be set to 2
sec/div. Use the large knob in the Horizontal control section to adjust the
time base. Read the time per division in the top central portion of the
display. The reading should show ‘2.00s/’ when properly adjusted. Now
use the small knob in the Horizontal control section to position the display
trace start time to 9.00s seconds (turn the knob counter-clockwise). Read
the time in the upper middle part of the display. The highlighted reading
should show ‘9.00s’ when properly set. In the Trigger control section
press the ‘Mode/Coupling’ button. Press the Softkey 1 three times to
select ‘Normal’. Use the small knob in the Trigger control section to set a
trigger level of ’20.3V’ as shown in the highlight in the upper right corner of
the display. Finally, press the ‘Single’ button in the Run Control section.
The scope is now ready to record voltages from the capacitor charging
cycle.
6. Turn the test box POWER switch ‘ON’.
7. Prepare the stopwatch (or wristwatch) for timing. You are to have one
team member use it to time the seconds from pressing the CHARGE
button until the indicator light comes on. Also, have another team
member watch the DMM reading and note the reading when the indicator
light comes on. A third team member should call out when the CHARGE
button is pushed and when the indicator light comes on. This allows the
other two members to just listen for the time ‘mark’ at which to record a
value. (The person doing the callouts should be the person to press the
button and watch for the light).
8. Press the black CHARGE button. The scope should begin displaying two
traces, one for the capacitor voltage and one for the indicator light voltage.
Remember to manually time the event as well. Record the values.
Manual Readings: Time _______ seconds
Voltage ________ volts
9. Wait for the “Run/Stop’ button to change to the color Red. Press the
‘Cursors’ button in the Measurement section. Cursors are dashed lines
that can be used to pick values from the display screen. There are two ‘X’
cursor lines (X1 and X2) and two ‘Y’ cursor lines (Y1 and Y2), but only one
set can be active at a time. The softkeys are used to select the particular
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set and line within a set. The small knob to the left of the ‘Cursors’ button
is used to move the chosen cursor line around on the display.
 Insure Softkey 1 shows ‘Normal’, Softkey 2 shows ‘1’, and Softkey
3 shows a checkmark under ‘X’.
 Press Softkey 4. Use the small knob to move the X1 cursor line to
where the CH 1 trace just begins to change from the reference
position (far left of the display).

Press Softkey 5. Use the small knob to move the X2 cursor line to
where the CH 2 trace makes a rapid ‘jump’. Read and note the X
reading from the lower left of the display screen.
1. Reading is _______ seconds.
2. Compare this value to the value you timed.
3. Are the two values representative of the same event ?
_________(Yes or No).
4. What is the percentage difference in your value
compared to the value from the scope? Percentage
Difference ____________ %. (Remember how to
compute a percentage difference: ((MyValueScopeValue)/ScopeValue)*100.
5. Which measurement method do you think is more
accurate and why?
10. Press Softkey 3 to select the “Y” cursors. Press Softkey 4 to select the Y1
cursor line. Move Y1 to the reference line (0.00V). Press Softkey 5.
Move Y2 to the point where the X2 cursor line intersects with the trace for
CH 1 (upper trace). Read and note the Y(1) reading at the lower right of
the display screen. Compare this value to the DMM reading you noted
earlier. How do they compare? How different are they and why are they
different? Include the answers in your report.
 Note the Y(1) value here: ___________________
11. Use the Y2 cursor line to pick the overall maximum capacitor voltage and
the corresponding CH 2 voltage.
 Note the values here:
 CH 1 _______ maximum, CH 2 ________.

Note the CH 1 and CH 2 voltages just before and just after the
‘jump’: CH 1 Before _________ CH 2 Before __________
CH 2 After _________ (Note: CH 1 is about the same
before/after).
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12. Mark the axes of the grid below to correspond to the oscilloscope display.
Label the axes with the variable (and units) being plotted (e.g. voltage in
volts and time in seconds). Mark the locations of zero (reference) for both
the time and voltage. Record the volts/div and time/div and mark the
gridlines on the axes accordingly. Make a sketch of the display. Your
sketch should be consistent with the data as recorded.
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1.4
Task 2 - Transient Measurement: Capacitor Discharge and Flash
This task will involve triggering the flash tube so DO NOT LOOK DIRECTLY
INTO THE TEST BOX WHEN PUSHING THE FLASH BUTTON !!! YOUR EYES
WILL BE DAMAGED IF THEY ARE EXPOSED TO SUCH BRIGHT LIGHT !!!
1. For the remainder of the measurements we will only use CH 1, so TURN
OFF CH 2 on the oscilloscope (press the CH 2 select button and the
select light should go out). You may disconnect the CH 2 test probe from
the test box but that action is not necessary. It is sufficient to simply
TURN OFF CH 2.
2. Adjust the display start time to 0.00s (use the small knob in the Horizontal
control section). Use the large knob in the same control section to set the
time per division to ‘200 S/’. Adjust the display start time to 600 S.
(You must follow this step or the start time may be ‘lost’).
3. Set the trigger level to ‘291V’. (Use the small knob in the Trigger control
section).
4. Press the ‘Edge’ button found in the Trigger control section. Then press
Softkey 1 just one time. (This will make the scope trigger (start) when the
input is decreasing through the set level).
5. Press the charge switch and make sure the capacitor has a full charge.
6. Press the ‘Single’ button in the Run Control section, then press the
FLASH button. A trace should immediately appear on the display screen.
7. Turn the test box POWER switch to ‘OFF’.
8. Press the ‘Cursors’ button and use the measurement cursors to get values
for the voltage column in the following table. Also record the "smallest"
capacitor voltage as measured at the end of the discharge trace.
Calculate the values for the other columns in the table. Remember Time
= 0 is when the trace begins its rapid decrease (not when the trace begins
on the display screen).
Smallest Voltage Value is __________ volts.
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Time
s)
Capacitor
Voltage
(volts)
t s)
V (volts)
I (amps) - see
below
0
100
100
100
200
100
300
100
400
100
500
100
600
100
700
1. The capacitor current is given by I  C
dV
.
dt
V
or
t
in words (current)  (value of capacitor)  (change in voltage) / (time
interval). The approximation is reasonable provided the time interval t
is small when compared to the overall time of the event.
2. Repeat the calculation for each of the time intervals in the table.
3. Do you observe any trends? Explain.
We can approximate the derivative in this equation to give I  C
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Mark the axes of the grid below to correspond to the oscilloscope display. Label
the axes with the variable (and units) being plotted (e.g. voltage in volts and time
in seconds). Mark the locations of zero (reference) for both the time and voltage.
Record the volts/div and time/div and mark the gridlines on the axes accordingly.
Remember that the time scale for this trace is different than for the previous
trace.
Make a sketch of the new trace. Your sketch should be consistent with the data
in your table.
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1.5
Task 3 - (Optional) Flash Trigger Measurement
This task is optional. If completed and included in the report, additional
points will be awarded.
The flash trigger signal is used to ‘fire’ the flash tube. The flash trigger
signal magnitude is greater than the 500 volt maximum for the scope. To
keep from damaging the scope, the signal must be reduced by some
method. This reduction is done for you inside the test box; but you must
understand how much the voltage is reduced so you can properly adjust
your values. The attenuation (reduction) is accomplished through a voltage
divider comprised of a 100 K resistor, a 1000 K (1 M) resistor, and the
1000 K input resistance of the oscilloscope.
Note: We would really like the input resistance of the oscilloscope to be
infinite, but since it isn't, and since its value is comparable to the other
resistors in the divider we need to account for the current going from our
circuit into the oscilloscope in calculating the voltage attenuation factor.
A schematic of the voltage divider is shown below. A 100 K resistor is in
parallel with the 1000 K input resistance of the oscilloscope. A 1000 K
resistor is connected in series with the parallel combination. The voltage to
be attenuated is Vtrig with the reference voltage Vref. The attenuated
voltage (Vdiv) is measured by the scope (VOscope) and the attenuation
factor is applied to get the value for Vtrig.
Vtrig
1000 K
Oscope
Vdiv
100 K
1000 K
Vref
Schematic
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of the voltage divider for the flash
trigger measurement.
10
The attenuation factor in this case is given by the following equation (where
K=1000):
VOscope
Vtrig

100K
 0.0833
1000K  100K  1000K 100K  1000K
1. Turn the test box POWER switch to ‘OFF’.
2. Remove the scope test probes and reference alligator clip from all test
points on the test box.
3. Connect the CH 1 test probe to the TP 3 ‘Flash Trigger’ test point.
4. Connect the CH 1 black alligator clip (reference) to TP6 ‘Capacitor+’.
5. Adjust the scope display start time to 0.00s (use the small knob in the
Horizontal control section). Use the large knob in the same control section
to set the time per division to ‘5.00 S/’. Adjust the display start time to 10
S. (You must follow this step or the start time may be ‘lost’).
6. Adjust the scope CH 1 reference position to mid-display (0.0V) by using
the small knob below the channel select button.
7. Adjust CH 1 vertical scale to ’20.0V/.’
8. Set the trigger level to ‘6.24V’. (Use the small knob in the Trigger control
section).
9. Turn the test box POWER switch ‘ON’ and PRESS the CHARGE button.
Make sure the capacitor has a full charge (voltage reading on DMM
greater than 300 volts).
10. Press the ‘Single’ button in the scope Run Control section, then press the
FLASH button. A trace should immediately appear on the display screen.
IMPORTANT: For this measurement you will need to divide your measured
voltages by approximately 0.0833 (or multiply by 12) to correct for the
attenuation provided by the voltage divider.
TURN THE TEST BOX POWER TO ‘OFF’
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Mark the axes of the grid below to correspond to the oscilloscope display.
Label the axes with the variable (and units) being plotted (e.g. voltage in volts
and time in seconds). Mark the locations of zero for both the time and
voltage. Record the volts/div and time/div and mark the gridlines on the axes
accordingly. Remember that the true voltage for this graph is not the same as
that shown directly on the oscilloscope screen. You should re-scale the
voltage axis by dividing by approximately 0.0833 (or multiplying by 12). Also
remember that the time scale for this trace is different than for the previous
traces.
Make a sketch of the trace.
Use the voltage (Y) and time (X) cursors to record the voltage and time of the
first 3 peaks and first 3 valleys of the displayed transient. Adjust the scope
voltages you recorded by applying the attenuation factor (0.0833) to get a
Corrected Voltage. The Corrected Voltage will be the actual trigger voltage
that existed in the circuit.
Time
Valleys
Voltage
Corrected
Voltage
Time
Peaks
Voltage
Corrected
Voltage*
It is important to note the reference test point was changed for this part of
the lab. The real trigger voltage value is the Corrected Voltage PLUS the
capacitor voltage value just prior to flash discharge.
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Turn the test box POWER switch to ‘OFF’. Disconnect all probes and leads.
Finish the hands-on part of the lab by turning OFF the oscilloscope and DMM
and cleaning-up the work area.
GENERAL INFORMATION:
For those so motivated, the oscilloscope does have a floppy disk drive that can
be used to save the scope traces. IBM formatted diskettes are used. They
following procedure may be used to save scope traces to floppy disk.
With CH 1 and/or CH 2 displaying a trace(s):
1.
2.
3.
4.
5.
Press the ‘Utility’ button.
Press Softkey 2 (‘Print Confg’)
Select ‘Disk’ with Softkey 1
Select ‘CSV Data’ with Softkey 2
Press ‘Quick Print’ button in the File control area
The data are saved in a .csv file with a name of ‘PRINT_xx’ where xx can be 01
through 99 depending on how many ‘PRINT’ files exist on the particular floppy. A
message is printed to the display when the data file is successfully ‘printed’. The
files are sequentially numbered by the scope software. These .csv files can be
directly opened in Microsoft Excel on a PC where you can manipulate the data in
any suitable manner. Then, you could even include charts in your lab reports for
instance.
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Report Instructions for Camera Lab 4
Your report should generally follow the lab report format handed out to you
earlier in the quarter. Specific instructions on what to include in each of the
sections follows. Write in sentences and paragraphs, not as a bulleted list, for all
sections of the report.
Team Report: This is a team report. Your entire team should submit one report.
Length: The written part of the report, not including the cover page or the tables
and figures (see below), should be about three to four pages long.
Cover Page: Include the names of all members of the team and your team
number.
1.6
Introduction
In addition to what is specified in the report format handout, include a
sentence giving the identifying number for the test box you used.
1.7
Experimental Methodology
Mention that an oscilloscope was used to record the behavior of the core
functions of the camera flash circuit. A DMM was also used for what?
1.8
Results and Description
1.8.1 Task 1: Charging Transient
 Description of the charging graph and table from Task 1. Be sure to refer to
the appropriate figure.
 How is the neon lamp turning on related to the data in the figure?
 Use Ohm's law to calculate the current flowing through the 3.9 M resistor at
the following times: 1) just before the jump in resistor voltage, 2) just after the
jump, 3) when the capacitor voltage was at its maximum value.
 Channel 1 of the oscilloscope has an input resistance of about 1M It was
connected in parallel with the 3.9 M resistor and therefore has the same
voltage across it. Calculate the current flowing through the input of Channel 1
at the same three times (Ohm's law again).
 Use the above two currents to estimate the current flowing through the neon
lamp at the same three times.
 Determine the voltage across the neon lamp at the same three times.
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1.8.2 Task 2: Flash Discharge Transients
 Description of the flash discharge graphs and tables from Task 2. Be sure to
refer to the appropriate Figure.
1.8.3 Task 3: (Optional) Flash Trigger Transient
 Description of the flash trigger graphs and tables from Task 3. Remember to
correct the voltages for the attenuation caused by the voltage divider. Be
sure to refer to the appropriate Figure.
1.9
Discussion

Discuss at least the following. You may add discussion of other
interesting observations.
1.9.1 Task 1: Charging Transient
 Any trends you observed.
 What happens to the capacitor during charging that causes the voltage to
change?
 What voltage is required to turn on the neon lamp?
 What else happens when the neon lamp turns on? Why does the neon lamp
resistor voltage ‘jump’?
1.9.2 Task 2: Flash discharge Transients
 Any trends you observe.
 After the capacitor is charged and the charging circuit has turned off, but
before the flash is triggered, the voltage on the capacitor will slowly decrease.
(Many minutes for it to fall so low that the neon lamp turns off.) What differs
in the path of the current for the flash discharge that causes the flash
discharge to be so much faster?
 Why doesn't the capacitor voltage go all the way to zero during the flash
discharge?
1.9.3 Task 3: (Optional) Flash Trigger Transient
 Make a table of estimates of the duration of charging, flash discharge and
trigger transients.
 Charging transient: The time it takes the voltage to go from zero to 90% of
its peak value.
 For the flash discharge transient calculate Vstart - (90%)(Vstart - Vend). Use
your graph to estimate the time at which this voltage is reached.
 For the flash trigger transient use one-half the time between the first peak
and valley.
 Compare the time scales for these three events with each other.
 Compare these time scales to the shutter and light flash speeds you
measured in an earlier lab.
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
Why must the flash trigger be so fast?
1.10
Summary and Conclusions

1.11
Follow the guidelines in the report format handout.
Figures and Tables
Include your figures and tables in this section. Put hand sketches here.
Start this section on a new page and attach it at the end of the report. Give each
figure a number and caption (e.g. Figure 1: Plot from Task 1). Also give each
table a table number and caption. If a table includes results of calculations,
include a sample calculation in the caption. It is OK to cut and paste the filled in
tables and figures from your Camera Lab 4 instructions. It is OK for the captions
and sample calculations to be hand written. However, you may want to
familiarize yourself with the equation editor tool in Word. It will be useful to you in
your future course work. Just like Tables and Figure, Equations get numbers
too.
Example:
 1

1
1
R parallel   

 ... 
 R1 R2 R3

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1
(Equation 1)
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