Directed Sequencer
In the sequencer examples previously the
control system ensured that the sequence of events happened at the correct
time and for the correct duration regardless of the consequences. What if
there was no water available for the washing machine ? What if there was
no traffic on one road and heavy traffic on the other ? Are we really
going to insist that the heavy traffic stop at a red light just to make
the other green for its allocated duration? Obviously not. The one thing
that is missing with pure sequence control is inputs. In the example
illustrated, the
sequencer for the washing machine could have an "input"
from a water sensor that detected the presence of water in the drum. If no
water was present it could be made to change or just stop its sequence and
perhaps sound an alarm. In this way we would have directed the sequence to
another path because of the status of an input.
With directed sequencers control starts to have the feel of machine
intelligence about it. No longer is the machine slavishly obeying
commands, but rather taking account of its environment and making
decisions about what to do next. The directed sequencer is probably the
most common form of automation found both in the domestic and industrial
environments. Typical examples include
Traffic lights that use sensors in the
road
Car washes that sense the position of
the vehicle before commencing and control the re-circulation of the
water bys sensing levels in tanks
Lifts/Elevators that decide on the
most efficient stop sequence based on button push
requests on each floor.
sequencer for the washing machine could have an "input"
from a water sensor that detected the presence of water in the drum. If no
water was present it could be made to change or just stop its sequence and
perhaps sound an alarm. In this way we would have directed the sequence to
another path because of the status of an input.
Car washes that sense the position of
the vehicle before commencing and control the re-circulation of the
water bys sensing levels in tanks
Lifts/Elevators that decide on the
most efficient stop sequence based on button push
requests on each floor.