Computer Software Module
UCCS Physics Labs
Table of Contents
Computer Startup
LabPro Interface
Logger Pro Program
Motion Detector
Photogate
Calibrating Sensors
Force Sensor
Accelerometer
Pressure Sensor
Getting Help
2
3
3
8
9
10
11
12
12
13
FYI
FYI
Astronauts are not allowed to eat beans before they go into space because passing wind in a spacesuit
damages them.
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Computer startup
This section will be an instruction manual for the lab computers and the software
we will be using this semester. If you have a good knowledge of computers and
windows then you only need to follow the steps. For those of you who are
unfamiliar or dislike computers read the full explanation for each of the steps.
• Turn on the power
To start the computer you first need to turn on the power. Computers
seem to have an endless variety of power switch locations, so this may not be
trivial to do for the first time. The computer may already be on first try move the
mouse and see it the computer wakes up. If this does not work the computer will
have to be powered up. To power up the computer push the larger of the two gray
oval buttons located in about the middle of the front panel of the computer. Some
lights will turn on and the computer will begin to go through its start-up
procedure.
• Starting Windows XP®
The computer should load the windows program automatically on boot-up.
If it fails to do to load Windows tell your instructor right away. You will need to
use your UFP account name and password. Be sure to log-off before you leave!
You can save any data files to your UFP account and access them later from any
other machine on or off campus (with a network connection to the campus). See
the IT department to setup your account or further information on the computer
network.
• Connecting the LabPro
Connect the power cord to the LabPro (lower left corner of the box). The
LabPro will make a series of beeps when it is powered up. The USB cable is
connected to the port on the middle of the right side of the box and to either port
on the back of the computer. Sensors connect to either the slots on the left
marked “Ch 1” to “Ch 4” or on the right side to the “Dig/Sonic” ports. Each
sensor has its own kind of plug if it does not work on one bank of inputs try the
other. DO NOT force a connection.
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How does the LabPro box work?
We live in an analog world, meaning that most of the
measurements we make are in the base 10 numbering system,
e.g.: 2.35 miles, -1038 kg, 0.0034 sec, etc. Computers are only
capable of understanding ON or OFF, or 1’s and 0’s. This is a
base 2 numbering system. The computer fools us into thinking
it knows more because it can display analog numbers. It does
this by combining large amounts of 1’s and 0’s, e.g.: 12 as seen
by the computer takes 4 digits: 1, 1, 0, 0. The problem
becomes, how do we get our measurements into the computer?
The answer is something called an Analog-to-Digital converter
(A/D for short). The LabPro box contains four of these A/D’s,
one for each input channel. An A/D does exactly what its
name implies; it can convert an incoming analog signal into its digital equivalent. This
digital number can then be transferred to the computer. The A/Ds in the LabPro are
capable of converting up to 70,000 readings per second and are 12 bits wide. The higher
the number of “bits” the more accurately it can convert an analog number into a digital
number.
The Logger Pro program
•
Open the Logger Pro program
•
Open the icon on the desktop that is called “Logger Pro 3.~”.
•
To open a program you need to double-click on the program icon. A
double-click is a rapid succession of two left button mouse clicks over
the program group or program icon.
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•
Opening screen
•
The first screen you will see is the default experiment window. It will contain
a data table and a graph window. If you already have sensors connected when
you start up the program the lab pro can detect them and might automatically
set up the window accordingly. Neat!
Menus: These are drop-down lists
of all the features in the program.
Data Table:
Data is
displayed in
a tabular
form.
Tool Bar: Contains buttons
of the most commonly used
functions in the program.
Plotter/Graph: Where
data is displayed in a
graphical format.
Clicking on the
numbers at the
ends of the axis
can change the
limits of the axis.
Figure 1 – Logger Pro opening screen.
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•
If you see the following screen it means the lab pro has not been setup
properly.
Or a window similar
indicating that the lab
pro is not connected.
•
Make sure the USB cable is firmly attached at both ends.
•
Make sure the interface has power.
•
If you still do not get a connection ask instructor for help.
The Menus
File menu
This menu is basic to most windows
programs. It contains the tools
needed to open, close, create and
save files. It also contains printing
commands and the exit
command.
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Experiment menu
This menu contains the tools needed to
setup and adjust the Lab Pro and
whatever sensors are connected.
The Toolbar
This is where you find the most used commands.
This is the most important button in the program!
This button starts the data collection process. Data collection will
only stop if the preset time limit is reached or the start button is hit
again (which will turn into a “stop” when running).
These tools are used to scale the graph. From left to right:
Auto scaling, Zoom in and Zoom out.
Auto scale: This button will adjust the graph so that all the
data will be shown.
Zoom in: If you want to get a closer look a part of a graph,
drag-out a box around the area and click on this button.
Zoom out: Clicking on this button will zoom out your view
of the graph.
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This button will bring up the sensor dialog box. From this
window you can select which sensor is connected to each of the
ports. The lab pro is capable of automatically detecting a sensor
when it is plugged in. Calibration of each of the connected
sensors can be also be performed from this screen.
I will write individual programs for each lab.
This toolbar will allow you to navigate through
the program pages.
Data Collection
Clicking on this button will bring up the controls for
the timing and data collection.
Use this dialog box to
set/adjust the total
collection time. Set the
data collection to stop
after the time expires or
repeat on a continuous
loop. Sampling rate and
collection triggering are
other options.
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Motion Detector (Sonic Ranger)
One of the most effective methods of describing motion is to plot graphs of
distance, velocity, and acceleration vs. time. From such a graphical representation, it is
possible to determine in what direction an object is going, how fast it is moving, how far
it traveled, and whether it is speeding up or slowing down.
In this experiment, you will use a Motion Detector to determine this information
by plotting a real time graph of your motion as you move across the classroom, as well as
a ball in freefall. The Motion Detector measures the time it takes for a high frequency
sound pulse to travel from the detector to an object and back. The computer takes this
information and calculates a distance measurement.
Figure 2: Motion Detector
It can then use the change in position to calculate the object’s velocity and acceleration.
All of this information can be displayed either as a table or a graph.
Motion Detectors are powerful tools for measuring the distances to objects and
exploring the laws of kinematics. They are easy to use if you keep two limitations in
mind.
1.) Min/Max Distance: The Motion Detector will have difficulty measuring
distances to objects that are less than about 15 cm or greater than 6 m away
from the sensor.
2.) Obstructions: The sound pulse is emitted in a cone from the front of the
detector. Make certain that the cone only intersects the object you are trying to
monitor. Keep other objects, such as the detector’s cord, the edge of the lab
table, or stools out of the sound cone.
Figure 3: Motion detector
cone of detection
Motion
detector
Object
Ultrasonic cone
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Photogates
A photogate is a very accurate and flexible timer. It projects a beam of light that
can record the time when the beam is blocked and for how long it is blocked. Big Deal,
right? Well just think back on experiments #1 and on how much trouble you had in
recording the time with a stopwatch accurately. Measuring a distance accurately is an
easy task with relatively simple and inexpensive lab equipment. Measuring the time is
the weak link in determining the velocity, and therefore the acceleration of an object.
The study of mechanics, which is the study of motion, requires you to know the velocity
and acceleration of objects. The following is a typical application of a photogate:
Time blocked
= 0.2654 s
Photogate
not blocked
by ball.
Ball’s leading
edge breaks the
beam of light.
Timing started.
Photogate
still blocked.
Timing
continuing.
Ball no longer
blocking
photogate.
Timing stopped.
The photogate will record the time the ball took to pass through the gate. If you
measure the diameter of the ball you can calculate the ball’s velocity (distance/time) with
great accuracy. When you think of photogates, think happy thoughts and have pity on
those before you who did not possess the power of the photogate.
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How do you Calibrate Logger Pro?
If you think back on how the Lab Pro box works, all sensors send signals back to
the Lab Pro that are only related to the real-world values, like Newtons.
Example: The raw data sent back from the force sensor is a voltage in the range
of –5 volts to +5 volts. What a calibration does is convert this raw voltage data into
something meaningful, like Newtons. The relationship between the raw data (voltage)
and needed data (Newtons) happens to be linear. Therefore, if we can find the equation
Useful data (Newtons)
of this relationship we can convert any raw data into useful data.
Calibration point
#2
#1
To calibrate the force sensor, we need to find
this calibration line. We need a minimum of
two points to define any line. The two easiest
forces to get are the force from a hanging mass
(measured with a well calibrated digital
Raw data (voltage)
balance) and zero force (nothing hanging from
the sensor).
Now that you know how a calibration works you can perform one by hand if
needed. However, this will take up too much of your time to do by hand. The Logger
Pro software has a calibration package, use it to calibrate any of the sensors.
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Calibrating the Force Sensor
ƒ
Connect a Dual-Range Force Sensor to the LabPro Interface. Set the Force
Sensor to the appropriate range by flipping the switch on the sensor. Each of the
range setting uses a different calibrating mass:
10N range
295 g mass (2.89 Newtons)
50N range
~1 kg mass (~9.81 Newtons)
ƒ
Choose ‘Experiment>>Calibrate…’ from the menu bar.
ƒ
Click on the Force icon. Click the
ƒ
Remove all weight from the Force Sensor and hold it vertically with the
button.
hook pointed down.
ƒ
Type 0 in the Value 1 edit box.
ƒ
When the displayed voltage reading for Input 1 stabilizes, click
ƒ
Add the 0.295 kg (2.89 N) mass to the hook of the Force Sensor.
ƒ
Type 2.89 in the Value 2 edit box.
ƒ
When the displayed voltage reading for Input 1 stabilizes, click
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Keep
.
Keep
.
Calibrating the Accelerometer
ƒ
Follow these steps to calibrate the Accelerometer:
ƒ
Choose ‘Experiment>>Calibrate…’ from the menu bar.
ƒ
Click on the Acceleration icon.
ƒ
Click the
ƒ
Point the arrow on the Accelerometer straight down. (It is important that
button.
the sensor is vertical and held steady. You may want to hold the sensor
against a table top to steady it.)
ƒ
Type – 9.81 in the Value 1 edit box.
ƒ
When the displayed voltage reading for Input 2 stabilizes, click
ƒ
Point the Accelerometer arrow straight up.
ƒ
Type 9.81 in the Value 2 edit box.
ƒ
When the displayed voltage reading for Input 2 stabilizes, click
then click
Keep
.
Keep
,
.
Calibrating the Pressure Sensor
ƒ
Follow these steps to calibrate the Pressure sensor:
ƒ
Choose ‘Experiment>>Calibrate…’ from the menu bar.
ƒ
Click on the Pressure icon. Click the
ƒ
Use the syringe with the Pressure Sensor to produce a pressure very near
button.
zero. The sensor has a 3-way valve at the end of a plastic tube leading
from the sensor box. With the syringe connected to position 3, align the
blue valve control to position 1 (see the diagram below).
2
1
3
Push the plunger on the syringe all the way in and move the blue stem
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control to position 2, thus closing both the syringe and Pressure Sensor to
atmosphere. To produce the near-zero pressure, pull the plunger out to the
20-cc position. If everything is sealed, the voltage reading should be very
near zero. If not, repeat this step.
ƒ
Type 0 in the Value 1 edit box.
ƒ
When the displayed voltage reading for Input 1 stabilizes very near zero,
click
ƒ
Keep
.
Open the Pressure Sensor to atmosphere by moving the blue valve control
to position 3.
ƒ
Enter the current atmospheric pressure in kPa (get this value from your
instructor) in the Value 2 edit box.
ƒ
When the displayed voltage reading for Input 1 stabilizes, click
then click
Keep
,
.
Getting Help On-line
You can always talk to your instructor for help!
If you need help and your lab instructor is busy you can get help using the
computer. You can use the help program located under the Help menu. Hitting the “F1”
key will also bring up the help program.
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