Lab #1
Measuring by Hand
Read Before Coming to Lab:
+ Resistors and Diodes (Chapter 1)
+ Resistor color codes (Chapter 2)
+ RS Multimeter Quick Start
+ The Thermister (Chapters 2 and 6)
+ The Thermocouple (Chapter 6)
+ Signal Generator Quick Start
+ Tek TDS210 Quick Start
Before you can begin learning instrument control, you must first know your instrument. You
must know what your instrument can measure, how to adjust it for best performance, how to
read the measurement correctly and how to estimate the uncertainty in the measurement. This
first lab consists of a series of hands-on exercises reading a DMM, producing a signal with a
signal generator, operating a power supply and an oscilloscope, and using some basic sensors.
Each exercise is given a suggested time for completion so you can pace yourself. We ask you, as
proof of your participation, to report your results on a Results Page that you will hand in to your
instructor at the end of the lab.
Exercise 0. Warm Up
Suggested Time for Completion: 10 min
Check List
Locate the equipment that should be placed at your
workstation. If any of the following items are missing
alert your instructor:
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One Radio Shack Manual/Auto Range digital
multimeter (DMM)
One Instek signal generator, Model GFG-8016G,
or its equivalent
One Tektronix TDS210 digital oscilloscope
One Agilent Technologies Programmable power
supply Model E3640A
One orange box with thermocouple and signal
conditioning circuitry
One orange box containing a chemical cell
A case of components (to be described in detail
below). This case is issued you for the duration of
the course; please keep it safe.
One silicon solar array mounted in a protective
frame and placed in a light-tight box (to remain in
the lab)
A box with four banana plug tie points for your
convenience in wiring circuits.
Banana and coaxial cables hanging up in the lab;
you will have to forage for what you need.
Many students use the physics lab and your workspace may have been left untidy. To get off to a clean
start do the following:
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If ON, turn any and all instruments OFF.
Clear away any and all connecting cables and
wires from all apparatus.
Examining the Components
See if you can identify the following items. In
particular…
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Identify the orange box with the attached K-type
thermocouple. The circuit contained in this box is
described in Chapter 6. The box is equipped with
plugs to enable it to be plugged into the DMM.
• Identify in the case the three carbon composition
resistors of nominal resistance 12 kΩ, a 200 Ω
resistor, two diodes (probably one of silicon and
one of germanium), one light-emitting diode
(LED) and one thermistor. If necessary, your
instructor will assist you in these identifications.
• Identify those values of the components by sight
or by color code that you can.
Let us proceed to Exercise 1.
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Lab #1
Exercise 1. DC Measurements
Suggested Time for Completion: 45 minutes
This exercise consists of taking a series of DC measurements with the DMM. In each case you are
welcome to connect the component you wish to study to two of the banana tie points on the box.
Then you can use banana cables to connect the two ends of the component to the DMM. As you
finish each task add your results to the appropriate spaces on the Results Page.
Using the Instrument
The front panel of the Radio Shack (RS) Manual/
Auto Range DMM is reproduced in Figure L1-1. In
the beginning, we shall give you detailed instructions
on how to use it. The number of these instructions
will diminish as you gain more experience and
become more independent.
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Set the DMM’s function/range switch to some
“Ω” position (200 Ω is probably best since you
expect the resistance of the cable to be small).
Insert one end of the cable into the “VΩ” socket,
the other end into the “COM” socket.
Turn the DMM ON and note the number on the
display. Don’t be surprised if you don’t get zero.
Using a connecting cable with a very small resistance as a load, you are reaching the lower limit of
what the DMM can accurately measure.
Using the range as a guide and the specification
sheet (Table A1-1) calculate the uncertainty in the
measurement. Does the result agree with zero
ohms to within the uncertainty?
Pull one end of the cable out from its socket on the
DMM and observe the display briefly. Can you
interpret what you observe? Insert the cable
again.
You can use a DMM to test if an electrical continuity
exists between two positions in a circuit. If it does (if
the resistance is less than a certain amount) the DMM
exits a ringing sound. To continue...
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Figure L1-1. The RS multimeter (Cat. No. 22-168A)
1 Measuring a Resistance
The resistance of components can vary over a wide
range, from the very small to the very large. Sometimes the instrument itself can affect the value of resistance obtained. You will measure the resistance of (i) a
length of connecting cable, (ii) a carbon composition
resistor, and (iii) the thermistor.
(i) Pick any length of connecting cable you can find
that has banana plugs on its two ends. Then do
the following:
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Rotate the range switch two positions counterclockwise to the “continuity test” position. This
position is indicated by a symbol of a musical
note on the panel. What do you observe?
+ Add your results to the Results Page.
(ii) Pick one of the carbon composition resistors and
deduce its resistance from the color code. Measure its
resistance with the DMM.
IMPORTANT: To get the most precise measurement
of anything with a DMM, always rotate the range
selector to the range that gives the maximum number
of non-zero digits in the display. This caution will not
be repeated in the instructions to follow.
Lab #1
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Calculate the uncertainty in the measurement.
+ Add your results to the Results Page.
(iii) For the thermistor do the following:
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Measure the resistance of the thermistor placed in
air (without you touching it).
Can you detect any evidence of self-heating
(heating of the thermistor by the DMM) or other
evidence of drift?
From the resistance vs temperature calibration
curve (Figure 2-10) estimate the temperature of
the air in the room.
Hold the tip end of the thermistor between your
fingers so as to heat it and observe the display on
the DMM. Does the number displayed increase or
decrease, that is, does the temperature of the
thermistor rise or fall?
+ Add your results to the Results Page.
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+ Add your results to the Results Page.
(iii) For the thermocouple do the following:
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2 Measuring a DC Voltage
Like resistance the voltage produced by a sensor can
vary widely. You will use your DMM to measure the
voltage of (i) your chemical cell, (ii) the silicon solar
array, and (iii) the thermocouple.
(i) For the chemical cell do the following:
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Set the function switch on the DMM to the
appropriate “V” position. You can anticipate the
voltage to be about 3.0 V.
Ensure the DMM is set to measure DC.
Plug the orange box with the chemical cell directly
into the DMM. The positive end goes to the “VΩ”
socket, the negative end to the “COM” socket.
Turn the DMM ON and measure the voltage.
Comment on the stability of the voltage. Is it constant to the 2 nd decimal place? 3rd decimal place?
+ Add your results to the Results Page.
(ii) For the silicon solar array do the following:
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Measure the DC output voltage when the array is
in the dark (with the cover in place) and then in
the light.
What happens to the voltage output when the
array is in the dark? You will no doubt conclude
that a silicon solar array is a good detector or
sensor of light.
Plug the orange box containing the K-type
thermocouple directly into the DMM.
Set the DMM to measure DC voltage on the 2V
range.
Allow the measuring junction to be free in air
(without you touching the end).
What value of voltage do you get from the DMM?
Calculate the room temperature from the calibration constants (Chapter 6).
Repeat the above with the thermocouple in the ice
bath.
Comment on the practicality of getting the icepoint temperature with an ice bath.
+ Add your results to the Results Page.
3 Measuring a DC Current
A silicon solar array delivers current as well as voltage. You will now measure the current delivered by
the array in a “Closed Circuit” state. Do the following:
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Ensure the DMM is set to measure DC.
Connect the array to the DMM with banana
cables. If you wish to get a positive reading,
connect the red output to the “mA” socket, the
black output to the “COM” socket.
Measure the current with the array in the light
and in the dark. Are your observations consistent
with what you observed earlier?
+ Add your results to the Results Page.
4 Testing a Diode
Good quality DMMs can be used to test and identify a
semiconductor diode. The voltage yielded by the test
will reveal if the diode is made from germanium or
silicon (Chapter 2). When a diode is tested with the
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Lab #1
diode oriented in the forward direction the DMM
displays the voltage that must be applied across the
diode in order to induce a current of 1 mA to flow
through it. Do the following:
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Set the function switch to the diode test position
(indicated by the diode symbol).
Connect the diode to the DMM (via the box), with
the end of the diode indicated by a band (cathode)
connected to the “COM” socket and the other end
connected to the “VΩ” socket.
Turn the DMM ON and read the display.
Repeat for the other diodes (including the LED).
From what you have learned about diodes from
Chapters 1 and 2 identify the diodes.
+ Add your results to the Results Page.
The main point to be learned from this exercise is that
a DMM can be used to measure many different things.
Thus far you have made DC measurements. Some
sources give a measureable output. Other sources, like
the thermocouple, require amplification before measurement for the most accurate usage.
We have seen in this exercise that a chemical cell is
the most common source of a DC voltage or a DC
current. But a DC voltage and a DC current can also
be obtained from a so-called power supply. We
continue in the next exercise with a first look at a newgeneration power supply whose output is controllable
from a computer. In keeping with the intent of this
lab, we shall concentrate here on the front panel controls you can activate manually.
Exercise 2. The Programmable Power Supply
Suggested time for completion: 30 min
This exercise will give you the opportunity of operating a modern high-quality power supply
manually. We assume you have worked your way through the Quick Start for the Agilent power
supply in Appendix A. In any case, you will be reminded of critical issues as we move along.
The Task
In the previous exercise you used a DMM to directly
measure the resistance of a carbon composition resistor. Now a carbon composition resistor is one of those
elements that obey Ohm’s Law (Chapter 1). That is to
say, the resistance of such an element can be calculated by measuring the voltage across the element and
the current through the element and then dividing.
The resistance is constant, independent of V and I.
You will do this here using the programmable power
supply.
With the power supply OFF,
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Connect the 200Ω 2W resistor to the output
terminals of the supply. (We shall use this resistor
instead of one of the 12 kΩ resistors since it will
result in a better resolution with the supply and it
has higher power rating.)
Turn the supply ON.
WARNING. If set incorrectly the supply has the
capacity of quickly destroying an element connected
to it. Therefore do the following...
When the supply is first turned on it goes into its
power-on/reset state, meaning the output is disabled
(the display shows output OFF) and the low voltage
range is selected (the instrument has two voltage
ranges 0 to 8V and 0 to 20 V). You can confirm this by
examining the lower left hand corner of the display
(“8V” is printed there). To enable the output...
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First Boot
Ensure the power supply is OFF before you begin.
To prevent confusion clear away any and all connecting cables and wires from all apparatus.
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Press the “Output On/Off” button.
Select the 20V range by pressing the Voltage
Range “High” button.
Lab #1
Notice at this stage that the display reads “00.00V”
and “0.000A”. The supply automatically displays the
voltage out and the current out. Resolution of thje
voltage is 0.01V and of current 0.001A. Also notice
that “CV” is printed at the right hand end of the display to indicate the supply is functioning as a constant
voltage source.
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Planning Ahead
When setting out to use this kind of programmable
power supply it is always a good idea to check to see
if there is any chance the device connected to the output may be damaged. In this case we are using a 200
Ω resistor of 2W capacity over a voltage range that
will not exceed 20 V. This means that the current
through the resistor will not exceed
Imax =
This happens to be the rating of the resistor (surprise!)
so the resistor should not be damaged at maximum
output. To continue...
20(V )
≈ 0.1A
200(Ω)
At maximum output the power dissipated in the
resistor will be
Pmax = ImaxVmax = 0.1(A)20(V)
= 2W .
Rotate the output control clockwise to increase the
voltage applied across the resistor.
At several values of output voltage between 0 and
20V note and record the output current.
Tabulate the ratio V/I.
+ Add your results to the Results Page.
Analysis
How well do your ratios agree with the expected
value of 200 Ω?
NOTE: Rather than calculate the individual ratios a
better strategy is to plot V vs I and fit a straight line to
the data. If time permits do this using the application
pro Fit (described in Appendix F).
+ Add your results to the Results Page.
When you have finished this exercise cleanup your
workstation.
Exercise 3. AC Measurements
Suggested Time for Completion: 2 hours
We assume you have worked your way through the Quick Starts for the signal generator and
oscilloscope in Appendix A.
Setup
The first task at hand is to set up the signal generator
and oscilloscope to display a working AC signal. Try
the following:
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Turn the signal generator ON and select a 1.000
kHz sinewave.
Set the amplitude control to about half-way up.
Use a coaxial cable to connect the output of the
signal generator to CH1 of the oscilloscope.
Turn the oscilloscope ON and perform an
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AUTOSET.
Manipulate the MEAS buttons so that the MEAS
boxes display the kind of information as shown in
Figure L1-2. (The actual numbers needn’t be the
same.)
Oscilloscope Measurements
The oscilloscope has an internal computer with which
it can measure a number of waveform parameters.
These measurements are displayed in the MEAS
boxes down the right hand side of the display. What
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Lab #1
is the frequency? What is the period? Is the frequency
number displayed really equal to the inverse of the
period number displayed? If the frequency and period
are not shown you will have to select them via push
button controls. Alert your instructor to explain how
to do this.
hand. How closely does the peak value and the rms
value obey the relationship:
Vrms =
Vpeak
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2
…[1]
+ Add your results to the Results Page.
Recall from Chapter 1 that this relationship should
hold only if the waveform is sinusoidal and has very
low distortion.
Triggering
Figure L1-2. A typical display on the Tek TDS210 DSO. At
this stage your oscilloscope display need only resemble what
is shown here.
Analysis By Hand
You can always check the oscilloscope measurements
by measuring the same parameters yourself with the
cursors the oscilloscope provides. To begin, switch the
oscilloscope to cursor mode (alert your instructor if
you don’t know how to do this) and invoke the
voltage (horizontal) cursors. Try measuring the peak
value of the waveform by manipulating the cursors by
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When you performed an AUTOSET above the oscilloscope was triggered automatically as part of the
AUTOSET sequence. Sometimes you will have to
trigger your oscilloscope by hand so it is useful to
know how to do this.
Most beginners on the oscilloscope find triggering
to be the trickiest function to master. A waveform displayed on the screen of an oscilloscope is said to be
triggered when it appears to be motionless. This
means that a waveform that appears to be moving to
the right or to the left is not triggered. To trigger a
waveform satisfactorily you need to set the timebase
control, the amplitude and the trigger level properly.
The trigger level is the voltage the input signal must
reach before the waveform is written to the screen. A
waveform can appear motionless only if the waveform is written to the screen beginning at the same
voltage level on each sweep cycle.
Lab #1
Results Page
Name:_____________________________
Student #:______________________
Exercise 1 DC Measurements
resistance ± uncertainty
continuity indication? (Y/N)
1 wire cable
color code: red, black etc.
value from Color Code
value ± uncertainty
1 resistor
resistance @ room temp
interpolated room temp
when heated, resistance rises?
1 thermistor
value ± uncertainty
stable to 2rd, 3rd place?
2 cell voltage
open circuit voltage ±
voltage with array covered ±
2 solar array
(air) voltage ± ∆v
air temperature (˚C)
2 thermocouple
(ice bath) voltage ± ∆v
ice-bath temperature (˚C)
2 thermocouple
current in the light
current in the dark
3 solar array
L1-7
Lab #1
voltage ± uncertainty
probable diode type
voltage ± uncertainty
probable diode type
voltage ± uncertainty
probable diode type
4 diode 1 test
4 diode 2 test
4 diode 3 test
Exercise 2 The Power Supply
V vs I Data for 200 Ω 2W resistor
Current I (Amperes)
∆I (Amperes)
Voltage V (Volts)
∆Voltage (Volts)
R = V/I (Ohms)
Results from Curvefit:
Exercise 3 AC Measurements
Volts (peak)
Volts (rms)
Volts (peak)
Volts (rms)
% Diff (from eq[1])
By scope
By cursor
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% Diff (from eq[1])
Lab #1
The graph area of a Tek TDS210 digital oscilloscope is reproduced below.
The scaling of the graph is:
each vertical division: 200 mV
each horizontal division: 500 µs
Using a pen indicate on the graph the
(i) peak-to-peak voltage
(v) trigger position
(ii) peak voltage
(vi) pre-trigger data
(iii) rms voltage
(vii) post-trigger data
(iv) period
Enter the following numerical values:
peak-to-peak value (V)
peak value (V)
rms value (V)
Voltage
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