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Distance = Rate * Time Since the carriage "Do-It-Yourself Lay-Down Whole Body Counter" always travels exactly the same distance in going from one end to the other, this value is a known constant. In fact, before you start the program, you must measure this distance so that you may enter it into the program when it is requested. For example, the total carriage travel distance of typical counter was found to be 71-15/16, or 71.9375 inches or 182.72 centimeters. Since we can measure the travel time required, the computer can calculate the speed and store it for later use in determining the equation of speed versus one of the above parameters. Normally, the distance would be stored in centimeters, however, in the Windows version of the "Helge" software, we are storing the distance in inches. The instructions for using the program are very simple and are contained within the program. The next section of this chapter shows the various screens obtained during the calibration of the carriage speed of a “Do-It-Yourself Whole Body Counter.”
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Starting the Speed Calibration Program
Speed Calibration, Figure 1
Before starting the program, go to the "Miscellaneous Parameters" paragraphs in the "Parameters" chapter. Make that the value of the "Distance Traveled" is entered.
Speed Calibration, Figure 2 Let us examine the contents of this page. In the upper left corner we have a selection entitled "Calibration Parameters." Enter the starting voltage, the ending voltage, and the incremental voltage per step. The program calculates the number of steps necessary. Continuing on the left column, the next group is "Direction." The default response is to select both "Right" and "Left." The next group in the left column Is "Status." The program shows that the starting voltage is 4.0 volts and the "Time," based on previous data that is still retained in memory, shows that the counting time should be about 73.5 seconds. This value will be changed the first time the carriage has moved from one end to the other. Just below the "Time," the program has sensed that the carriage is at the left limit switch and it knows, therefore, that the carriage must move to the right. The next grouping on the left column is headed "Calculations." At the end of the travel of the carriage on each of the various passes, the measured values will be entered in these columns, except for the very first passage because you must have a minimum of two passages in each direction to make your first estimate of the slope, intercept, and correlation coefficient. You should be aware that the equations for speed may be different between travel to the right and travel to the left. If the floor on which the whole body counter rests is not completely level, a motor drive assembly will have to work harder when pushing the carriage uphill. You may ignore the "Show Switch Status" and the rest of the information in the left column. On the very bottom line there are five boxes. The only one of importance now is the "Start" box. Click this and the rest of the entire calibration procedure is automatic. The next two screen captures will show the first right hand pass and the first left hand pass. After each pass the results will be entered in the column headed "Calibration Results." Let us now look at those two screens.
Speed Calibration, Figure 3 The very first pass, moving from left to right, has been completed and the results are shown in a center column. Notice that the X and Y coordinates are automatically graphed. The units of the y-axis coordinates are "inches per second."
Speed Calibration, Figure 4 The first set of left and right passes have been completed and the results are shown in a center column. If you keep an eye on the "Status" group, you will see that the voltage changes polarity and magnitude as the steps progress.
Speed Calibration, Figure 5 The first two sets of left and right passes have been completed and the results are shown in a center column.
Speed Calibration, Figure 6 The first three sets of left and right passes have been completed and the results are shown in a center column. Note that we now have two sets of equations along with their correlation coefficients. As can be seen from the slope editor steps, there are very slight differences between the speed equations.
Speed Calibration, Figure 7 The first four sets of left and right passes have been completed and the results are shown in a center column.
Speed Calibration, Figure 8 The first five sets of left and right passes have been completed and the results are shown in a center column.
Speed Calibration, Figure 9 All six sets of left and right passes have been completed and the results are shown in a center column. The equations for each direction of travel are given in the "Calculations" panel. It is these equations that will be used to determine the voltage sent from the computer to the motor speed control so that the counting time will be very close, within a few seconds, to that chosen by the operator. |
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