This is the first of two exercises in which you
determine if the limit switches on a pair of slide
gates have been wired correctly. In this exercise,
the system uses indicator lights to show the
positions of the gates. In the following exercise,
the system uses a monitor display.
The shipping bin model shown on the right has
been re-wired. If it has been wired properly, the
behavior of the indicator lights should match the
truth table shown below. Your job is to determine
if it has been correctly wired.
The truth table below is composed of text entry
fields. To modify a field, move the cursor over
it, click the mouse, and type the letters you want
to insert. When you press the "enter" key or click
the mouse over a different part of the screen, the
changes will become permanent. To perform the
test, begin with the first line of the truth table
and make sure the actual positions of the Ship and
Return gates match the positions specified by that
line. Then note whether each of the four indicator
lights is lit (on) or not lit (off). If the on/off
condition of the light does not match the
condition specified in the truth table, mark that
field with an "X," as was done for the previous
example of miswired gates, and mark that line of
the table as incorrect by typing an "X" or a "NO"
in the last field of the line (under the "OK?"
heading). If all four indicator lights are
correct, mark the entire line as correct by typing
your initials in the field under the "OK? heading.
If you make a mistake, the computer will tell you.
The previous version of miswired limit switches
probably represents a simple mistake. Although it
can allow the elevator to take back good grain
that has been charged to the customer, it can just
as easily allow the elevator to unintentionally
give away grain. However, the gates shown here
have been wired so that the Return Gate is shown
closed whenever the Ship Gate is fully open. At
the same time, the "Full Open" indicator light for
the Return Gate is disabled, so nobody could
notice that both the "Closed" and "Full Open"
lights were on at the same time and get
suspicious. This setup can only divert grain back
to the elevator.
NOTE: If the model
does not appear below you do not have a VRML player