Car parking systems are becoming increasingly automated, especially in urban environments and commercial buildings. Programmable Logic Controllers (PLCs) play a crucial role in managing these systems efficiently. This article delves into a PLC program designed for a car parking system, using RSLOGIX 500 as the programming environment. We will explore the logic, components, and functionality of a basic car parking system controlled by a PLC, providing a foundational understanding for automation enthusiasts and professionals.
This example system manages two garages, each with a capacity of 5 cars. The PLC program is designed to monitor car entries, track the number of cars in each garage, and signal when a garage is full. This ensures smooth operation and prevents overcrowding, directing drivers to available parking spaces.
Inputs and Outputs for PLC Car Parking System
To effectively control the car parking system, the PLC interacts with several input and output devices. Here’s a list of the essential inputs and outputs:
Inputs:
- Gate 1 Entry Sensor (Input I:0/0): Detects a car entering Garage 1.
- Gate 1 Exit Sensor (Input I:0/1): Detects a car exiting Garage 1.
- Gate 2 Entry Sensor (Input I:0/2): Detects a car entering Garage 2.
- Gate 2 Exit Sensor (Input I:0/3): Detects a car exiting Garage 2.
- Master Start Push Button (Input I:0/4): Starts the car parking system operation.
- Master Stop Push Button (Input I:0/5): Stops the car parking system operation.
Outputs:
- Garage 1 Filled Lamp (Output O:0/0): Indicates Garage 1 is full.
- Garage 2 Filled Lamp (Output O:0/1): Indicates Garage 2 is full.
- Parking Closed Signal (Output O:0/2): Indicates both garages are full and parking is closed.
- Gate 1 Entry Gate (Output O:0/3): Opens the entry gate for Garage 1.
- Gate 1 Exit Gate (Output O:0/4): Opens the exit gate for Garage 1.
- Gate 2 Entry Gate (Output O:0/5): Opens the entry gate for Garage 2.
- Gate 2 Exit Gate (Output O:0/6): Opens the exit gate for Garage 2.
PLC Logic Description for Car Parking System
The PLC program logic is designed using RSLOGIX 500 and is broken down into rungs to manage different aspects of the car parking system.
System Start-Up and Master Control
RUNG 000: Master Start/Stop Latch
This rung uses a latching mechanism to control the overall operation of the car parking system. Activated by the Master Start push button and deactivated by the Master Stop push button, this rung ensures the system operates only when intended.
Garage 1 Control Logic
RUNG 001: Gate 1 Entry Activation
When the Gate 1 Entry Sensor detects a vehicle, this rung activates the Gate 1 Entry Gate, allowing the car to enter Garage 1.
RUNG 002 & RUNG 003: Garage 1 Car Count and Full Indication
These rungs implement a counter to track the number of cars entering Garage 1. For each entry detected by the Gate 1 Entry Sensor, the counter increments. If the count exceeds 5 (the capacity), the Garage 1 Filled Lamp is turned ON, indicating that Garage 1 is full. This uses an up counter to accumulate the number of cars.
RUNG 004 & RUNG 005: Garage 1 Exit and Count Reduction
When the Gate 1 Exit Sensor is activated, signaling a car leaving Garage 1, this rung activates the Gate 1 Exit Gate and uses a down counter to decrement the car count for Garage 1. This ensures accurate tracking of available spaces.
Garage 2 Control Logic
RUNG 006 – RUNG 010: Garage 2 Operation
The logic for Garage 2 mirrors that of Garage 1. These rungs manage entry and exit through Gate 2, count cars in Garage 2, and activate the Garage 2 Filled Lamp when Garage 2 reaches its capacity of 5 cars. It follows the same principles of counting and gate control as Garage 1, ensuring consistent management across both parking areas.
Parking Full Indication
RUNG 011: Parking Closed Signal
This rung monitors the status of both Garage 1 and Garage 2 Filled Lamps. If both lamps are ON, it means both garages are full. In this case, the Parking Closed Signal is activated, informing drivers that no parking space is available in either garage.
Key Points on the Logic:
- Counters: Up counters are used to increment the count on car entry, and down counters are used to decrement on exit. This provides a real-time count of cars in each garage.
- One-Shot Instructions: While not explicitly shown in the simplified rung descriptions, in a practical application, one-shot instructions would be used with the entry and exit sensors to ensure that each pulse from the sensor is counted only once, even if the sensor remains active for a longer duration. This prevents multiple counts for a single car.
- Interlocking: The system uses interlocking concepts to ensure that gates operate correctly and counts are accurate, preventing errors in parking management.
Conclusion
This PLC program example for a car parking system illustrates the fundamental principles of using PLCs for automation in parking facilities. It demonstrates the use of counters for tracking vehicles and logic for managing entry and exit based on garage capacity. While this is a simplified example, it provides a solid foundation for understanding how PLC programming can be applied to create more complex and efficient car parking management systems. This program can be further expanded to include features like displaying available spaces, payment systems integration, and more advanced security measures, showcasing the versatility of PLC in automation.
