Download Bike Lab #3 - Gateway Engineering Education Coalition

Introduction to Engineering
Bike Lab # 3 - 1
Agenda
 Analog and digital recording and
displays
 Presentation of Bike Lab #3
Procedure
Engineering Measurements
Quantities that engineers need to measure:
Strain
Force
Pressure
Moment
Torque
Displacement (position)
Velocity
Acceleration
Flow velocity
Mass flow rate
Volume flow rate
Temperature
Frequency
Color
pH
O2 level
Engineering Measurements
MECHANICAL
MEASUREMENT
SYSTEMS
ELECTRONIC
Advantages of electronic measurement systems:
• Potentially more accurate
• Provide an electrical output that can be stored,
transmitted, or used for control
Analog and Digital Display and Recording
 Physical quantities can be displayed or recorded
by analog or digital means.
Analog:
 Measured quantity is displayed and/or recorded
continuously
 Can have any value within a range.
 Examples: tire pressure gage, analog
speedometer, analog bathroom scale, stripchart recorder, cassette tape.
Analog and Digital Display and Recording
Digital:
 Measured quantity is displayed with discrete
resolution.
 Can be recorded at selected times
 An output signal is converted to a number that
can be stored using digital code
 Accuracy of the record depends on the
resolution (number of bits) and frequency of
sampling (how often a record is made)
 Examples: digital speedometer, digital
bathroom scale, music CD.
Analog and Digital Display and Recording
Strip-chart recorder
Analog and Digital Display and Recording
Analog and Digital Display and Recording
Analog and Digital Display and Recording
Analog and Digital Display and Recording
Digital speedometer of a
Harley Motorcycle
Components of an Electronic
Measurement System
Transducer
Conditioning
Circuit
Converts
measured
quantity
(mechanical,
thermal,
chemical etc.)
to measurable
electrical
quantity
Amplifie
r
Recorder
Amplifies
conditioner
output
Converts
transducer
output to
electrical
quantity to
be amplified
Records
amplifier
output.
Recorder
may be
analog or
digital
Data
Processing
Computer
analysis,
display
graphs,
tables
Digital Recording
3 Bits, sampling every 20 seconds, full scale 7 V,
resolution 1.0 V (FS/7)
AMPITUDE (V)
7
Original signal
6
5
4
Recorded
Signal
3
2
1
0
0
10
20
30
40
50
60
TIME (s)
70
80
90
100
Digital Recording
3 Bits, sampling every 10 seconds, full scale 7 V,
resolution 1.0 V (FS/7)
Original signal
AMPLITUDE (V)
7
6
5
4
Recorded
Signal
3
2
1
0
0
10
20
30
40
50
60
TIME (s)
70
80
90
100
Digital Recording
AMPLITUDE (V)
4 Bits, sampling every 5 seconds, full scale 7.5 V,
resolution 0.5 V (FS/15)
Original signal
7
6
5
Recorded
Signal
4
3
2
1
0
0
10
20
30
40
50
60
TIME (s)
70
80
90
100
Digital Recording
AMPLITUDE (V)
5 Bits, sampling every 5 seconds, full scale 7.75
V, resolution 0.25 V (FS/31)
Original signal
7
6
5
Recorded
Signal
4
3
2
1
0
0
10
20
30
40
50
60
TIME (s)
70
80
90
100
Part II - Measuring load on a bicycle fork
Loads applied by rider
STRAIN GAGE
A sensor that
measures strain
When the bicycle is loaded (a person is riding), the fork is
loaded. Due to the load, the fork deforms. The STRAIN
GAGE is used to measure the strain in the fork.
Loads on a Bicycle Fork
Loads applied by rider
Compression
Bending
Loads applied by the road
Shearing
The fork is loaded
by a combination
of compression
shear and bending
Transducer: Strain Gage
The strain gage is a resistor.
Its resistance changes if its
length changes.
Measured Quantity: strain
Measurable Electrical Quantity:
resistance.
The strain gage is cemented to
the bicycle fork. When the
bicycle is loaded the fork is
strained and the strain gage
resistance changes
Backing Film
Grid
(electrical resistor)
Copper-plated
Solder tabs
Conditioning Circuit: Wheatstone Bridge
 The strain gages are connected as the four
resistors in the Wheatstone Bridge.
 The bridge converts the change in the strain
gage resistance to an output voltage (Vout) that
is proportional to the strain in the fork due to the
bending loading.
 The output voltage is fed to an amplifier.
Conditioning Circuit: Wheatstone Bridge
The change in the output voltage from the Wheatstone
Bridge is related to the strain of the strain gage by:
Vout  Vin  A  S g
where:
Vin  7.6 Volts
 is the strain
A  460 (amplificat ion ) Vout is the change in the voltage
S g  2.085 (gage factor)
The equation can be solved to give the strain as a function of
the output voltage.
Conditioning Circuit: Wheatstone Bridge
The stress (s) in the fork can be calculated from
the strain (), by using Hooke’s law:
s  E
Where E is the Modulus of Elasticity
For the bike fork material E = 29.0 x 106 psi.
In Our
Experiment:
Strain
Gage
Transducer
Converts
measured
quantity to
measurable
electrical
quantity
Wheatstone
Bridge
Conditioning
Circuits
Amplifier
Converts
Amplifies
transducer
conditioner
output to
output
electrical
quantity to
be amplified
Recorder
Records
amplifier
output.
Recorder
may be
analog or
digital
Data
Processing
Computer
analysis,
display
graphs,
tables
Measuring Load on a Bicycle Fork
In Lab:
The goal in this lab is to find a correlation
between the weight of the bicycle rider and
the stress/strain due to bending in the front
fork.
Lab Procedure
1. Set up the data logger as described in the
instruction sheet
2. Collect voltage data with the data logger for
each member of your group. Use the following
sequence for tests (all times are approximate):
In the riding position: the feet are on the pedals and the
hands are on the handle bars.
Lab Procedure
 Use the following sequence for collecting voltage
(all times are approximate):
 5 seconds for an unloaded bike.
 5-10 seconds for rider 1 in riding position (no
pedaling).
 15 seconds for rider 1 pedaling
 5 seconds for unloaded bike.
 5-10 seconds for rider 2 in riding position (no
pedaling).
 15 seconds for rider 2 pedaling.
 Repeat
Lab Procedure
3. Unload the data from the data logger to
the PC and save it to a disk.
4. Import the data into Excel and save it as
a spreadsheet.
After Lab
1. In the spreadsheet, create a column of
time data as described in the data logger
instructions.
2. Draw the raw voltage data vs. time and
identify each event on the graph, i.e.
unloaded bike, rider 1 gets on, rider 1
sits on bike, rider 1 pedals bike, etc…..
3. Calculate the strain at each data point.
After Lab
4. Calculate the stress at each data point.
5. Create a graph of stress vs. time. Label
your graph.
6. Using average value of stress for each
rider in the riding position while pedaling,
create a plot of stress vs. weight of each
rider. Create a linear trend line for the
data and show the equation of the line on
the graph.
After Lab
Prepare a team Lab Report using the
standard format given and include the
following:
 Plot of raw voltage data with activities labeled
 Plot of stress vs. time
 Plot of stress vs. rider weight with trend line
equation
 First page of spreadsheet (don’t include all
pages of data)
 Sample calculations (calculating strain from
voltage, calculating stress from strain)
Assignment
 Read Bike Lab #3 Procedure carefully!