How Allen Bradley PLCs and Siemens PLCs use timer instructions and the ample differences

Sample Solution

   

Timers as Logical Devices

Timers are fundamental logic devices that measure time intervals. They are widely used in various applications, including automation, control systems, and embedded systems. In the context of PLCs (Programmable Logic Controllers), timers play a crucial role in controlling time-dependent processes and sequences.

Timers are typically implemented as counters that increment or decrement at a predetermined rate, such as once per millisecond or second. The counter value represents the elapsed time since the timer was started or reset. When the counter value reaches a predefined preset value, the timer triggers an output signal.

Full Answer Section

      Timer Implementation in Studio 5000 Studio 5000 Logix Designer is the primary programming environment for Allen-Bradley PLCs. It provides a comprehensive set of instructions, including timers, for controlling and programming PLC systems. Timers in Studio 5000 are represented as TON (Timer On-Delay) and TOF (Timer Off-Delay) instructions. These instructions have similar functionalities but differ in their triggering behavior.

• TON (Timer On-Delay) Instruction: The TON instruction starts counting once its input condition is met and continues counting until the preset value is reached. When the preset value is reached, the timer's output signal turns on, and the accumulated value is reset to zero.
• TOF (Timer Off-Delay) Instruction: The TOF instruction starts counting immediately and continues counting until the preset value is reached. However, the timer's output signal remains on as long as the input condition is met. When the input condition goes false, the timer starts counting down. Once the countdown reaches zero, the timer's output signal turns off.

Types of Timers in Studio 5000 Studio 5000 offers various types of timers to cater to different application requirements. These timers include:

• Retentive Timers: Retentive timers retain their accumulated value even when the PLC loses power or the program is interrupted. This ensures that the timer continues counting accurately even after power cycles or program restarts.
• One-Shot Timers: One-shot timers trigger their output signal only once for a specified duration after their input condition is met. Once the output signal turns on, it remains on for the preset time and then turns off automatically.
• Counting Timers: Counting timers count up or down instead of timing a specific duration. They are often used for counting events or measuring cycles.

Input and Output Signals of Timers Timers typically have two main input signals and one output signal:

• Enable (EN) Input: The EN input controls whether the timer starts or stops counting. When the EN input is high, the timer starts counting; when it is low, the timer stops counting.
• Preset (PRE) Input: The PRE input sets the desired time interval for the timer. The timer continues counting until the accumulated value reaches the preset value.
• Done (DN) Output: The DN output indicates whether the timer has reached its preset value. When the DN output is high, it signifies that the timer has completed its timing cycle.

In addition to these basic input and output signals, some timers may have additional inputs or outputs for advanced control functions. Conclusion Timers are essential components of PLC programming, enabling the control of time-dependent processes and sequences. Studio 5000 provides a comprehensive set of timer instructions, including TON, TOF, retentive timers, one-shot timers, and counting timers, to address diverse application requirements. Understanding the different types of timers and their input and output signals is crucial for effectively utilizing timers in PLC programming.