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many relays interconnected to other relays for opera- tion (Figure 2). There were many complex, hardwired circuits. One relay in a chain would fail, sometimes intermittently, and a fault would occur, but it would be difficult to find the cause of the fault. It was a frus- trating control system to support, with the intermittent faults the worst of many problems.
Figure 2: Relays
There were several control panels full of hardwired relays and accompany- ing wiring, causing intermittent problems which were di cult to diagnose.
Sequence of Operation
The ride sequence requires two sets of cars (trains) to alternate. When in automatic mode, the system
is run with one start button and one forward but-
ton on the last zone of the ride. The ride can be started with a loaded train in the start (loading) area and an empty train in the unload area, immediately upstream of the start.
The start button is pressed and the 3-car train
is released. The chain drive drags the train to the
top of the hill where it runs free and coasts until the last zone is reached. The last zone is the unloading area. Once the loaded train clears the start area, the empty car can be sent forward and is ready for new riders to board.
The braking system was previously an all pneu-
matic system operating friction brake pad mech- anisms at appropriate points in the ride. The new design still uses pneumatic brakes in several loca- tions, but a few were replaced with magnetic brakes which require no external control, just adjustment
to slow down the train at key points of the ride. The starting and endpoints still have pneumatic brakes, as well as electromagnetic brakes within the motors themselves.
Upgraded Control System
An AutomationDirect (www.automationdirect. com) Click PLC was chosen to replace the old PLC and many of the relays. The PLC is used in a “dual- rack” configuration and controls all ride operations. It also controls the air compressor system and brak- ing systems, and monitors the position of the trains in the ride.
The PLC monitors positions of the train cars, and determines whether to allow them to proceed to the next station (blockzone) in the ride.
All the compressed air system monitoring was replaced with new pressure switches, and program- ming in the new PLC was added to monitor and verify all pneumatic and electromagnetic brakes are operating when and where required. The new con- trol system monitors for air pressure problems, and for brakes failing to operate when required. Should the braking systems fail to register as activated, the control system will create an alarm and shut down the ride.
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All E-stops and related safety relays are also mon- itored by the PLC, and can shut down the ride any time they are activated. Safety relays are used in the power systems, as well as during the release of the cars at the starting point. The safety relays operate power contactors to energize the five motors used throughout the ride. These contactors also energize the variable frequency drive used to control the chain drive motor pulling the train up the hill at the start of the ride. The unloading station also includes safety relays monitoring the lap bar release system.
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