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Computer-Based Laboratory




Probeware

The computer is a tool that is commonplace in real-world science labs and their use in the classroom allows students to conduct science in an authentic atmosphere. The computer-based laboratory utilizes a computer, a data-collection interface, electronic probes, and graphing software, allowing students to collect, graph, and analyze data in real-time. This real-time atmosphere allows students to attend to and process important details in each experiment.





LabPro Computer Interface

LabPro is a data collection interface that has three different connections. The first connection supplies power to the LabPro through an AC adapter when used in the classroom, but the LabPro can also run on 4 AA batteries if used remotely, such as collecting data while riding a roller coaster. The second connection transfers data from the LabPro to the computer via a USB cable, but the LabPro can also be connected to a TI graphing calculator or used as a stand-alone data logger.







The third connection links LabPro to various
data-collection probes (listed separately below) through its four analog channels (CH1, CH2, CH3, and CH4) and two digital channels (DIG/SONIC 1 and DIG/SONIC 2). The probes send electrical signals to LabPro. Logger Pro, a software package, takes the signals from LabPro and interprets them numerically. Data can then be studied in tabular form, graphical form, or both.




Motion Detector (Sonic Ranger)

This probe sends out an ultrasonic signal (inaudible to humans) that bounces off of objects and back to the detector. This signal fills a cone-shaped area about 15 to 20° off the axis of the center line of the beam.

Based on a) the time it takes the signal to make a round trip from the detector to the object and back to the detector and b) the speed of sound, Logger Pro can determine the distance between the detector and object at any given clock reading.




This probe has limitations:
  1. It has a range between 10 cm and 6 m.
  2. Care must be taken to avoid spurious signals. Some troubleshooting tips are listed below:
    • Make sure that the motion detector is not directly beside the computer monitor. RF signals from the monitor may interfere with the detector.
    • Remove any objects that may reflect the signal prematurely—it will collect data for the closest and/or largest object in the signal cone.
    • Note that the signal cone extends downwards which can be a problem when using the detector on a hard, horizontal surface. If this is the case, try pivoting the motion detector slightly upward.
    • Place a soft cloth just in front of and below the motion detector to absorb spurious signals.
    • Change the data collection rate.
    • Affix a large, flat, vertical surface to the object being studied to better reflect the signal.
  3. Technically, this probe must be calibrated to the temperature at which the probe is being used (temperature affects the speed of sound), but for the range of temperatures found in the physics room, this effect will be negligible.
Motion detectors are connected to LabPro using a DIG/SONIC channel. While the motion detector is operating, you will hear a clicking sound and a green LED on the face of the detector will light. The clicking is a result of the gadget that is producing the ultrasonic signal, and it's frequency is dependent on the signal rate.

The motion detector also has a sensitivity switch (shown at right). The switch will, for most objects, be set to the ball/person icon. The only time you might set the switch to the cart icon is when studying low friction environments with the dynamics cart/aluminum track system.




Photogate

A photogate contains two diodes; one emits an invisible infrared signal and the other detects the infrared signal. This signal is aimed across the threshold of the photogate such that the signal will be interrupted by an object (known as a flag) passes through the gate. The interruption or resumption of the signal (as seen by the detecting diode) is read by the Logger Pro software. This probe is usually used to measure time intervals. If one photogate is used, the time interval recorded is the time during which the signal was blocked. If two photogates are used, the time interval recorded is usually the time between when the first gate is first blocked and when the second gate is first blocked.

The modular phone jack of the connecting cable inserts into the photogate housing and the other jack inserts into one of LabPro’s DIG/SONIC channels. To test the operation of the photogate, block the infrared beam and check that the red LED found in the photogate housing is on or check the status bar at the bottom of the main Logger Pro window.

Photogate Accessory: Picket Fence

A picket fence is a rectangular piece of plastic with alternating black and transparent strips. The function of the black strips is to block the infrared beam of the photogate, and the function of the transparent strips is to allow the infrared beam to pass through to the detecting diode.

When passing through the photogate, LoggerPro starts timing when the beam is first blocked and will record the clock reading associated with each consecutive block of the beam. By running the picket fence through a photogate, 8 different events of position and clock reading can be collected. Picket fences can be used as stand-alone objects as well as attached to a dynamics cart.

Photogate Accessory: Smart Pulley

The smart pulley is a spoked pulley attached to a photogate. The pulley serves the same function as a picket fence; the spokes block the infrared beam of the photogate and the openings between spokes allow the infrared beam to pass through to the detecting diode. Like the picket fence, the spacing between the front edge of each spoke is constant and LoggerPro will start timing when the infrared beam is first blocked. An unlimited number of clock reading and position events can be collected.







Dual-Range Force Sensor

This probe is used to measure the force between two objects. It can measure either a push or a pull. When a force is applied to the probe, a small plate inside of the probe bends. The amount of bending is dependent on the amount of force applied, much like the extension or compression of a spring is dependent on the amount of force applied. The force probes are calibrated so that Logger Pro can compare measured forces and the amount of strain they exert on the small plate to a known force and the amount of strain it exerts on the small plate.

These probes can measure force in a range between 0.01 N and 50 N. They are attached to LabPro through any of the four analog channels (CH1 – CH4).




Wireless Dynamic Sensor System (WDSS)

This probe contains a force sensor, a 3-axis accelerometer, and an altimeter. It communicates with a computer and LoggerPro software using a Bluetooth wireless connection. The wireless connection removes the problem of cords dragging along a surface as found on a conventional force probe and the internal battery allows the user to program the probe to work remotely. While in the classroom we typically use only the force sensor, but the accelerometer and altimeter suite is ideal for using remotely while riding roller coasters, bungee jumping, or skydiving. The 3-axis accelerometer provides information about the g-factor the rider experiences throughout the ride while the altimeter provides a profile for the ride, providing a record of where the rider is along the ride (on hills, in valleys, in loops, etc.)

The WDSS communicates with other devices via Bluetooth, which requires either a Bluetooth-ready device or a Bluetooth dongle, a small receiver that connects to a computer through a USB port.



Light Probe

This probe can be used to measure the intensity of light being emitted from any light source. The switch on the box allows you to select the intensity range appropriate for any given light source:

0-600 lux is used for low levels of illumination
0-6000 lux is generally appropriate for indoor light levels
0-150,000 lux is mainly used for measurements in sunlight.

The light sensor is attached to LabPro through any of the four analog channels (CH1 – CH4).