Design a PLC ladder diagram for a parking garage counting th

Design a PLC ladder diagram for a parking garage counting the cars coming in and going out. There must be a green light indicating room to park in the garage. When it has 24 to 25 cars, a yellow light will turn on. When the garage reaches 25 cars, a red light will come on. Also, when it rains, a red light will indicate that the garage is closed with the red light.

Solution

The PLC p g ro ram is executed as part of a repetitive process referred to as a scan. A PLC scan starts with the CPU reading the with the CPU reading the status of inputs. The application program is executed using the st t f th i t O th tatus of the inputs. Once the program is completed, the CPU p g erforms internal diagnostics and communication tasks. The scan cycle ends by updating the outputs then starts over The outputs, then starts over. The cycle time depends on the size of the program, the number of I/Os, and th t f i ti d the amount of communication required. •PLCs invented to Replace Relays and HARD WIRING: Prior to PLCs, many of these control tasks were solved with contactor or relay controls