30 May 97
Melvin Price Locks and Dam has a semi-automatic
(9) Next the PLC checks the filling valves for
lockage control system in place and operational.
closure and closes them if necessary.
Following is a description of the system:
(10) The PLC now opens the emptying valves.
(1) The operator initializes the command PRE-
The chamber is again monitored for comparison to
PARE UPSTREAM END FOR ENTRY/EXIT.
(2) The PLC first checks the downstream miter
(11) When the chamber has reached the level of
gates for proper miter. If the gates are not mitered,
the tailwater, the PLC opens the downstream miter
the PLC starts the miter gates and brings them to
miter. The downstream traffic light automatically
goes to RED.
B-2. Potential Problems of a PLC System
(3) Next, the PLC checks both emptying valves
to ensure they are closed. If they are not, the PLC
a. Higher skill required. The design, operation,
starts the valves and closes them.
maintenance, and modification of the PLC system
will require higher skill levels. Electrical engineers
(4) The PLC now opens the filling valves and
and technicians will require skills associated with
monitors the water level in the chamber for compari-
computer circuit design, system analysis, electronic
son to the pool elevation. Water level indication is
engineering, and computer programming. Lock main-
accomplished using a submersible pressure
tenance personnel will need to be upgraded from
electricians to electronics technicians. These higher
skill levels require increased compensation to attract
(5) To prevent overfilling of the chamber, the
PLC begins closing the filling valves with about a
3-ft difference between the pool and chamber
b. Commitment. The successful installation and
operation of a PLC system requires management to
provide top down policy direction for financial, per-
(6) When the chamber water level reaches that
sonnel, and training resources to successfully imple-
of the pool, the PLC lowers the lift gate or opens the
ment this system. The successful implementation of
the PLC system requires a workforce of lock opera-
tors, lock maintenance technicians, electrical engi-
(7) After the vessel is completely in the lock
neers, and electronics technicians who are fully
chamber and properly secured, the operator initiates
committed and willing to champion this concept. If
the command PREPARE DOWNSTREAM END
these basic requirements are not satisfied, a PLC
system may not live up to expectations or could even
be a bug-ridden failure.
(8) The PLC first closes the upstream gates.