EGR 101
Resistance Experiment
• READ this before class on Thursday
1
Reminder about Teaming
• Share the technical load
• Make sure each team member
understands what’s going on
2
Digital Multimeter (DMM)
Used to measure the following:
Voltage – DC and AC
Current – DC and AC
Resistance
Capacitance
Temperature – w/ extra probe
Also used to check:
Diodes
Transistors
3
We’ll Use the DMM to Measure
Resistance
• Resistors restrict the flow of current, given a
fixed voltage
• Unit = Ohms, Ω
• They come in different packages
4
Color Code
• The resistors we’ll test have a color code
to identify their resistance and tolerance.
5
Resistor Color Band Code
Band 1 (closest to the end) – first
digit
Band 2 – second digit
Band 3 – power of ten multiplier
(most cases simply the number of
zeros)
Band 4 – tolerance (Red = 2%,
Gold = 5%, Silver = 10%, none =
20%)
Color
Value
Color
Value
Black
Brown
Red
Orange
Yellow
0
1
2
3
4
Green
Blue
Violet
Gray
White
5
6
7
8
9
6
What is “Tolerance” about?
• If a resistor has a nominal value of 1000 Ω
and a tolerance of ± 10 % then individual
resistors with the same nominal value are
allowed to vary in their actual values from
900 Ω to 1100 Ω and still be considered
acceptable.
• Any resistor fabricated with an actual
value outside that range should be
rejected as “not meeting specifications”.
7
Ultimate Goal of this Exercise
• To generate a histogram demonstrating
how many of your resistors meet
specifications.
• A histogram is a plot that shows how many
of an item fall into specific “bins”.
8
Example Histogram
Table Generated by Excel
Raw Data
Value
1
1000
2
1050
3
990
4
1075
5
950
6
899
7
1102
8
1080
9
1005
10
1020
Number of
resistors with
values < or =
to 900
Bin
Number of resistors
with values from
1051 through 1100
Frequency
900
1
950
1
1000
2
1050
3
1100
2
More
1
Plot of Excel Table Data
Histogram for 1000 Ohm Resistors
3.5
Number in Range
R#
3
2.5
2
Frequency
1.5
1
0.5
0
900
950
1000
1050
Measured Value
1100
More
9
Practice Problems
•
•
•
•
Brown Blue Red =
Yellow Violet Gold =
33 k Ohms =
1.8 Ohms =
10
Resistance Experiment – Part 1
(45 minutes)
• Each team will be given a package of resistors.
• For each resistor,
– Determine the expected value of resistance by
applying the color code.
– Measure the actual value of the resistance by using
the ohmmeter function on the Digital Multimeter.
– Compare the actual and expected values of
resistance – does the actual value fall within the
allowable range?
– Enter your results in an EXCEL table, as shown on
the next page.
11
Data for Resistance Lab – Part 1
Names:
ITEM #
Team #
NOMINAL
VALUE
TOLERANCE
ALLOWABLE
RANGE
MEASURED
VALUE
VARIATION
(in %)
1
2
3
4
5
6
7
8
9
10
Eg: 450-510 Ohms
Determined from color band
code
Leader:
Timekeeper:
Recorder:
100*(Meas-Nom)/Nom
12
Resistance Experiment – Part 2
(55 minutes)
• Each team will be given a sample of
resistors having the same nominal value.
• For each resistor:
– Determine the nominal value from the color code.
– Measure and record the resistance of each resistor in
the sample.
– Enter your data in an Excel table (sheet 2) as shown
on the next page.
– Plot a histogram bar graph of the measured values
and determine the mean and the standard deviation
of the resistance values.
13
Data for Resistance Lab – Part 2
TEAM #
NAMES
NOMINAL VALUE
TOLERANCE
=
ALLOWABLE RANGE
MEASURED
VALUE
1
2
3
4
5
6
7
8
9
10
=
=
AVERAGE
STD DEV
Leader:
Timekeeper:
Recorder:
14
Preparing to Plot a Histogram
• Before you start to generate a plot,
generate a sequence of 5 numbers in your
Excel sheet, equally spaced, from the
minimum of your allowable range to the
maximum of your allowable range.
• For example, if my range was 400-800, I
would generate the following sequence:
400
500
600
700
800
15
Generating a Histogram Table
• Click on the “Tools” pull-down menu
• Select “Data Analysis”
– (If you don’t see Data Analysis, click Mcrosoft logo,
click excel options at the bottom, select “Add-Ins” and
then select “Analysis ToolPak”)
• Select “Histogram”
• For Input Range
– Enter the cell range with your resistance
measurements (e.g. a4:a20)
• For Bin Range
– Enter the cell range of your 5 values
• For Output Range
– Enter the cell that you want to be the upper left corner
of your histogram table
16
Generating a Histogram Plot
• Select (click and drag the cursor over) the table
that was created using the histogram command
• Click on the “Insert” pull down menu
• Select “Chart”
• Select “Column” chart type (default), click “next”
• You’ll see a preview of your plot, click “next”
• Enter a label for the x axis and change the plot
title from “frequency” to something with your
nominal resistor value in it, click “next”
• Select “as object in sheet 2” in last step then
click “finish”
17
What needs to be turned in:
• Everyone's practice problems
• A printout of the data table from the 1st
experiment
• A printout of the data table from the 2nd
experiment including:
– The original data
– The histogram table
– The histogram plot
• Each participating team member needs to
print and sign his/her name
18