Most things show variation even if they are of the same type. Humans vary in height and weight, manufactured articles vary in their characteristics. In this example we shall take a sample from a population of light bulbs to find out how much they vary. It should then be possible to see if this variation is great or small.

Materials

Set up the following electric circuit using the Calculator, CBL2 and voltage probes as a voltmeter.
 

1. Plug the Voltage Probe into channel CH 1 on the CBL2 interface.
    
2. Start the DataMate program. Press to reset the program. DataMate will detect the auto-ID sensor, set the data collection parameters, and display the current sensor reading.
    
3. Press : SETUP and using the cursor
   buttons, or select MODE press
    
4. In the SELECT MODE menu choose : SELECTED EVENTS.
    
5. Press : OK to return to the main screen.
   

Collecting data

1. Select 15 light bulbs at random. Screw the first light bulb into the socket.
    
2. Select : START to begin data collection. Press to record your first measurement.
   
   
3. Change the light bulb and press . to record your second measurement
   
   
4. Continue until you have recorded the voltage across all 15 bulbs. Make sure you do not measure the same bulb twice.
    
5. Stop data collection by pressing the key.
   
6. Save your data in the usual way (5: TOOLS then 1: STORE LATEST DATA RUN)
7. To view the data quit Datamate and press then 1: EDIT. The list of voltages will be in L2 (and a copy in L3). Rename the file and then save it in archive. Now it can be analysed statistically.

• MPI Index
• Top of Page