appendix b: mbl hardware and software [out of date] · 2005. 5. 17. · appendix b: mbl hardware...

© 1992-93 Dept. of Physics and Astronomy, Dickinson College Supported by FIPSE (U.S. Dept. of Ed.) and NSF Portions of this material may have been locally modified and may not have been classroom tested at Dickinson College.

APPENDIX B: MBL HARDWARE AND SOFTWARE

[OUT OF DATE]

I. USING MACINTOSH MBL SOFTWARE – EVENT COUNTING AND EVENT TIMING

A. Overview – What Are Microcomputer Based Laboratories? In most modern experimental laboratories, electronic sensors are used to collect data automatically. Sensors are used to time events, detect movement, and count beta particles emitted from radioactive nuclei. Sensors can also be used to measure temperatures, light levels, voltage, current, and many other quantities. It is possible to attach sensors to electronic circuitry that allows the sensor signals to be interpreted by micro-computers. This is a very, very powerful capability, because microcomputers can analyze the signals mathematically and display the results rapidly and automatically in either numerical or graphical form. By coupling the collection of real data with a symbolic representation of it in the form of a graph, you can obtain an immediate picture of how the data is changing in time and thus better understand the significance of the data as it is being collected. As part of the Dickinson College Workshop Physics project, started in the fall of 1986, a special interface unit (referred to as the Universal Lab Interface (or ULI) and computer software have been designed to bring signals to the Macintosh computer from a Geiger counter, a photogate sensor that can be used for timing events, an ultrasonic motion detector, a force sensor, and a temperature probe. The hardware and software used to empower microcomputers to sense, process, and analyze signals from the outside world have come to be known as Microcomputer Based Laboratory equipment (or MBL). We are still in the process of developing the MBL circuits and computer software for the Macintosh computers. In this manual, we will describe two MBL's developed for the Macintosh computer: (1) a counting system for recording beta particles and other "events", and (2) a timing system for recording the rate at which an object passes through a device known as a photogate. Eventually this manual will be updated to describe new Macintosh MBL equipment as it is developed.

Workshop Physics II: Appendix B – MBL Hardware and Software Page B-2 Authors: P.W. Laws, P. Rosborough, R.J. Boyle, & S. Sanborn V2.0.7/93 – 5/17/05




B. Information on the Universal Lab Interface The ULI is a serial interface developed by Ron Budworth of Transpacific Computer Company for curriculum development projects at TERC, Dickinson College, and Tufts University. It features compatibility with most of the familiar TERC MBL sensors distributed by HRM and Queue. It is also compatible with several new sensors developed at Dickinson College and Tufts University. The ULI can be linked to any host computer with an RS232 or 422 modem port, as well as to the 16 pin dip game paddle ports on Apple IIe/II plus computers. Thus, the same interface and sensors can be used with the Apple II, Macintosh, and IBM Compatibles.

Power Digital In Voltage In Digital Out Resistive In

RCA

Jacks

Universal Lab Interface

Top View

Universal Lab Interface

On

LED

STATUS LED

A/D CONV

RAM

EPROM

ADR

LATCH CPUPLD

R/C TIMER8 BIT

LATCH

9v POWER

RECEPTICLE

EXPANSION

PORT

Port 1 Aux Port 2

1 2

TCC

RS-232

1 2 1 2 1 2 1 2

ON/OFF SWITCH

DIN 1

DIN 2

Power for IR LEDS

plug in here (Red Plug)IR sensors (yellow) and

Geiger Counter plug in here

Note: The firstIR sensor plugs in Digital In 1,

the second in Digital In 2

V



C. Setting Up the ULI

Supplying Power: To supply power to the ULI, you should attach the 9V power transformer into the appropriate power receptacle in the upper right hand corner of the ULI unit and plug the 9V transformer into a 110 VAC outlet. Connecting the Unit to the Macintosh Computer: To connect the ULI to the Macintosh, you should attach the 25 pin modem cable to the serial port on the right side of the ULI and the round 8 pin connector to the modem port of the Macintosh. Turning the ULI On: To turn the ULI on, flip the toggle switch in the upper right corner of the ULI to the left.



II. EVENT COUNTING WITH A GEIGER COUNTER

A. What is a Geiger Counter? A Geiger counter is used for detecting the presence of gamma particles or beta particles that are emitted from the nuclei of atoms. It consists of a tube from which the air has been removed and to which argon gas has been added. The tube has an electrode in it which can be placed at a high voltage. When a beta or gamma particle passes through the Geiger tube, electrons are ripped away from the argon atoms and attracted to the high voltage electrode. The burst of electrons that results can trigger electronic circuits to send out a signal that can be detected as an "event". The small Geiger counter used with the MBL Event Counting System is a battery operated Heathkit Model RM-4 Radiation Monitor. It consists of a Geiger tube housed in a plastic case along with electronic circuitry, an audio beeper, and a rate meter.

B. The Macintosh Version of the MBL Event Counter for Nuclear Radiation Detection The Macintosh MBL Event Counter when used for radiation detection consists of —

• A Macintosh computer • a ULI (serial interface to bring electronic signals from the Radiation Monitor to the Macintosh computer) with a communications cable and a power supply • A Heathkit RM-4 Radiation Monitor & a radioactive source • MBL Event Counter software (MacNuke) developed at Dickinson College

The set up is shown in the diagram below —

RadioactiveSource

GeigerTube

MBLInterface



C. The Macintosh Event Counter Hardware and Software (V3.1) The Radiation Monitor, ULI, and computer should be hooked up properly before data can be collected. To do this —

1. Plug the ULI into the modem (telephone) port at the back of the Macintosh Computer. Make sure the 9V power transformer is plugged in properly. Turn the ULI on by flipping the switch located in the lower right hand corner. 2. Plug the Radiation Monitor into the ULI by inserting the phonojack into digital input #1. 3. Turn on the Radiation Analyzer by sliding the switch in front to the right.

The Event Counter software was developed by Brock Miller at Dickinson College. To open it, you should:

1. Turn the Macintosh on. 2. Open the Workshop Physics Folder and find the Event Counter program. (It is usually in a folder called MBL, or some such.) 3. Double click on the Event Counter icon.

D. Software Summary You can produce a display of the number of counts in a pre-designated time interval as a function of time. This is shown in the graph on the next page, in which the time interval was set for one second. The graph shows that from 0-1 seconds 5 nuclear events were detected by the Radiation Monitor, from 1-2 seconds only 2 nuclear events were detected, and so on. The Run Time was preset to 10 seconds even though only 8 seconds is displayed on the sample graph. The average of the 10 Counts/Interval values that were recorded turned out to be 3.0 with a standard deviation of 1.2 Counts/Interval.



You can also display a Distribution plot which consists of a histogram of the number of times each possible number of Counts/Interval was observed. This is shown in the diagram below for a situation in which 600 counting intervals were recorded. Although the diagram below doesn't have a scale on the vertical axis, the histogram shows that a Counts/Interval of 29 was observed the most times, while a Counts/Interval of 16 was observed only once and so on.

Data for the Counts/Interval vs. time and for the Times Observed v. Counts/Interval can be displayed in either graphical or tabular form. Displaying Data and Pasting it into Other Software for Analysis The display of a graph of Counts/Interval vs. time, or a graph of Times observed vs. Counts/Interval can be set up either before or after data is collected. Once data is collected it can be displayed in a table. The resulting data table can be copied into the clipboard and later pasted into a spreadsheet or other graphing software for further analysis.

E. Becoming Familiar with the Event Counter Software 1. Getting ready to record Counts/interval vs. Time: Follow the instructions in Section II.C. of this manual to plug in the Radiation Monitor and load the Event Counter Software v.1.0.b for event counting. When the software is loaded, you should see a Counts/Interval vs. time graph on the computer screen which has been pre-configured for an interval of 1 second and a 10 second run time.



2. Collecting Data: Place the radioactive source close to the wire mesh that protects the window to the Geiger tube in the Radiation Monitor. Verify that the ULI has been turned on, and click on the Start button at the bottom of the screen to start counting some of the beta and gamma particles emitted from the source. Watch what happens during the next 10 seconds. Repeat this step and move the source around a bit until you understand how the location of the radioactive source affects what is happening on the screen. 3. Displaying a Data Table: To see the data you collected in a data table simply select Table in the Display window. 4. Configuring the Data: To change the configuration of the data either before or after you collect it, select any of the following items from the Configure window:

• Run Time: You can choose the total elapsed time for your experiment from a range of times that varies from as little as 1 second to as much as 24 hours. You can choose the maximum number of times observed you expect to record on a distribution graph from 10 to 5000. • Interval: You can choose the time interval over which successive counts will be recorded from a range of intervals that varies from 1/20th of a second up to 60 minutes. • Counts/Interval: You can choose the maximum number of counts/interval that you might expect to have to accommodate on a graphical display of an experiment from 10 to 1000. You can estimate this by collecting some sample data.

5. Displaying the Frequency Distribution: Play with the Distribution feature, which provides a histogram of the number of times observed for each of the counts/interval values you obtained. To do so, select:

• Distribution in the Display window • Table in the Display window • Graph in the Display window

6. Transferring Data to the Clipboard and other Programs: Practice placing data in the clipboard or scrapbook by selecting the appropriate type of Data Table in the Display window. Now pull down the Edit window and highlight Select All. Then select Copy from the same window. The data will now be in your clipboard and you can use normal procedures to Paste it into another program or into your clipboard.



7. Saving Files: It is possible to save data files along with graph scaling factors. To do this, pull down the File menu and select Save. You will then be asked to name your file.



8. Retrieving Files: To reload a file you should already have opened the Event Counter application. Then pull down the File menu and select the Open option. Then select the file you want to open. 9. Printing Data and Graphs: To print your data table or graph you should display the table or graph you want. Then pull down the File menu and select Print.



III. EVENT TIMING WITH PHOTOGATES A. How Does an MBL Photogate Work? A photogate is a device that can be used with a microcomputer to measure time intervals with more accuracy than a stop watch can. For example, a microcomputer can be programmed to calculate the time it takes for strips of tape mounted above a moving cart to pass through a photogate. These times can then be 'saved' by being written into a data file on your disk. Later you can read these times from your disk into a spreadsheet.

A photogate consists of an infrared light-emitting diode (or IR LED) and a light sensitive device called a photodetector. They are placed opposite each other in a rig as shown below. A timer can be started when the IR light shining on the photodetector is interrupted and stopped when the beam is restored. Thus, we can measure the time it takes for an object to pass by the photogate. If the size of the object is known, its average speed can be calculated. Furthermore, if the direction of motion is known, then you can determine the velocity of the object from its speed.



All computers are run by accurate clocks that can be "read" with special programs. Electrically, a photodetector acts like an open switch when it is in the dark and like a closed switch when it is flooded with light. If a photodetector is attached to an input line on a microcomputer, the computer can be programmed to keep track of the time interval when light is blocked from a photogate. This use of the computer's input is probably less entertaining but more useful than zapping aliens! B. The Macintosh Version of the Photogate Event Timer The Macintosh MBL Event Timer consists of —

• A Macintosh computer • A ULI (a serial interface box to bring electronic signals from the photogate to the Macintosh ) with a communications cable and a power supply • A photogate system – holder, IR LED, photodetector • MBL Event Timer software developed at Dickinson College

C. The Macintosh Event Timer Hardware and Software

The photogate, serial interface, and computer should be hooked up properly before data can be collected. To do this:

1. Plug the ULI into the modem (telephone) port at the back of the Macintosh. Make sure the 9V power transformer is plugged in properly.



Turn the ULI on by flipping the switch located in the upper right hand corner of the unit.



2. Plug the photodetector into the ULI by inserting the yellow phonojack into digital input #1. Obtain power for the infrared LED by plugging the red phonojack into one of the ULI receptacles labeled POWER. (Note: If you want to use two photogate systems at the same time you can follow the same procedure and plug the second photodetector into digital input #2 in the ULI.) 3. Set the photodetector and IR LED opposite to each other in the photogate holder.

The Event Timer software was developed by David Egolf at Dickinson College. To open it, you should:

1. Turn the Macintosh on. 2. Open the Workshop Physics folder and find the file called Event Timer in one of the available folders. 3. Double click on the MBL Event Timer Icon to open the Event Timer software.

D. Software Summary You can produce a graph of raw data showing when a photodetector is blocked and when it is unblocked as shown below.

You can also configure the data collection to allow the micro-computer to calculate time intervals, ∆t, that are of interest. For example, you may be interested in the time interval between the time the gate is blocked and the next time it is blocked for each time those two types of events happen. These times can be displayed on a graph or in a data table as shown below in which two such time intervals were recorded.



Setting the Configuration Setting the configuration in the event timer software determines which time intervals are calculated for further display and analysis. The user may designate either one or two different sets of time intervals (i.e., configurations), to be calculated by the computer. These time intervals are denoted ∆t1 and ∆t2. To choose a configuration:

1. Select Configure... from the Set Up window. 2. If you want 2 configurations, click on the box marked Two Configurations. 3. To configure ∆t1, set the Start Condition by clicking inside the rectangle to the right of Start Condition, and select which gate and gate condition you want to start the timing. 4. Set the Stop Condition by clicking inside the rectangle to the right Stop Condition, and select which gate and gate condition you want to stop the timing. 5. Select the number of passes between each time interval that is selected. Ordinarily you should leave this at the pre-selected value of 1, but if you are doing timing for a pendulum, you may want to set this at 2 or some larger value so the computer will determine ∆t1 by selecting the 2nd, 3rd, or so on, occurrance of the stop condition. 6. If you have selected 2 configurations, you will want to set the start, stop, and number of passes for ∆t2, as well.



Designating Display of Special Functions of Time Intervals The photogate timing system is highly useful for measuring velocities and accelerations of rapidly falling objects. A special feature of the software allows a user to enter a constant c into the computer that represents the distance between strips of tape. Then the user can choose a function, f(x) involving c and a time interval ∆t. This function will be plotted or placed in a data table. Two particularly useful preselected functions are vel(x) and acc(x) representing velocity and acceleration, respectively. One possible relationship between time intervals that the user has preconfigured and velocity and acceleration is shown in the diagram below.

(b) If c is the distance from the leading edge of one tape to the leading edge of another and ∆t is the time interval from the block to block condition on the photodetector, then the average velocity of the lucite strip as it passes the gate can be computed at the average time at which the two leading edges passed by the photodetector. If several such average velocities are calculated, then the average acceleration for successive pairs of tapes can be calculated. Displaying Data and Pasting it into Other Software for Analysis The display of a certain function can be set up either before or after the user designates a configuration for the determination of time intervals, determines a run time, and collects data. The resulting data table can be copied into the clipboard and later pasted into a spreadsheet or other graphing software for further analysis.



E. Becoming Familiar with the Event Timer Software 1. Displaying a Graph of Raw Data: Follow the instructions in Section III.C. of this manual to prepare the photogate system and load the Event Timer Software. When the software has loaded, you should see a Raw Data graph on the computer screen that has been preset for a 10 second Run Time. 2. Collecting Data: Verify that the ULI has been turned on and click on the Start button at the right edge of the screen and then click the mouse to start data collection. During the 10 seconds after clicking the mouse, wave your hand back and forth inside the photogate rig. Watch what happens. Repeat this step until you understand how blocking and unblocking the photogate affects what is happening on the screen. Note: On your initial run, the program will require you to calibrate the photogates by blocking and then unblocking them. Follow the directions on the screen. 3. Changing How the Raw Data is Displayed: Play with the following display features for the graph that is created when you select Start and cause the photogate to be blocked and unblocked by selecting one at a time: • Run Time in the Set Up window • Magnified Data in the Graph 2 window • Full Height or Half Height in the Graph 1 window 4. Magnifying the Raw Data Graph: Play with finding times and time intervals on a Raw Data graph that has been created by selecting Magnified Data from the Graph 2 window and clicking the mouse on the rectangles with arrows in them or using control, arrow, and tab keys. 5. Displaying Time Intervals vs. Time: Play with the display of a graph of the preset time intervals on gate 1 by selecting f(t) from the Graph 1 window. (Note: The time intervals have been preset so that the start condition for measuring a time interval is blocked and the stop condition is also blocked.) To change the configuration that is displayed, select Configure... from the Experiment window. For example, try changing the configuration so the start condition for determining an interval is blocked and the stop condition is unblocked. It is suggested that you play with the following features for displaying



the graph and table of the time intervals you have designated by selecting one at a time: • Range in the Graph 1 or Graph 2 windows • Show Table in the Table window • Full Height or Half Height in the Graph 1 window



6. Displaying Special Functions vs. Time: Play with displaying functions of the configured time intervals by selecting one at a time– • f(t) in the Set Up window • Enter c... in the Set Up window • f(t) in the Graph 1 or Graph 2 windows • ∆t1 in the Graph 1 or Graph 2 windows • Range in the Graph 1 or Graph 2 windows • Resolution in the Graph 2 window • Show Table in the Table window • Full Height or Half Height in the Graph 1 window 7. Transferring Data to the Clipboard and other Programs: Practice placing data in the clipboard or scrapbook by displaying a data table and using Select All. Then select Copy in the Edit window. The data will now be in your clipboard and you can use normal procedures to Paste it into another program or into your clipboard.

appendix b: mbl hardware and software [out of date] · 2005. 5. 17. · appendix b: mbl hardware...

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