You have explored the architecture of Allen Bradley PLCs and the core instructions that these PLCs have including the basic relay instructions, latch and unlatch instructions, one shots, timers, and counters. In this discussion, you will focus on timers how Allen Bradley PLCs and Siemens PLCs use timer instructions and the ample differences in these two PLCs implement timers.
Explain Timers as a logical device. How does Studio 5000 implement Timers as a PLC instruction? What are the different types of Timers in Studio 5000? Explain their input and output signals.
Full Answer Section
Types of Timers in Studio 5000
Studio 5000 offers a variety of timer instructions, each tailored for specific applications and control requirements. The primary types of timers include:
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TON (Timer On Delay): This timer activates its output after a specified time interval has elapsed. The output remains energized until the timer is reset.
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TOF (Timer Off Delay): This timer deactivates its output after a specified time interval has elapsed. The output remains deactivated until the timer is reset.
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TTO (Timer Two-Shot): This timer activates its output for a specified time interval upon receiving a rising edge on its input. The output remains energized for the preset duration and then deactivates.
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TPE (Timer Pulse): This timer produces a pulse of a specified duration upon receiving a rising edge on its input. The output activates for the preset duration and then deactivates.
Input and Output Signals
Each timer instruction has specific input and output signals that define its behavior and interaction with other control elements. The common input signals include:
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EN (Enable): This input signal controls the overall operation of the timer. When energized, the timer starts counting the time interval.
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Preset: This input signal defines the duration of the time interval. The timer counts until the value of the preset is reached.
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Reset: This input signal resets the timer, causing it to stop counting and return to its initial state.
The common output signals include:
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Done: This output signal indicates that the timer has completed its time interval and is ready for a new cycle.
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Out: This output signal represents the state of the timer's output. The output is energized or de-energized depending on the timer's type and current state.
Comparison of Allen-Bradley and Siemens Timers
Allen-Bradley and Siemens PLCs, two prominent brands in industrial automation, employ different approaches to timer implementation. While both systems offer a variety of timer instructions, there are notable distinctions in their programming and functionality.
Allen-Bradley Timers
Allen-Bradley timers are characterized by their user-friendly programming and straightforward operation. They are typically represented by function blocks in Studio 5000, providing a visual representation of the timer's elements and connections. Allen-Bradley timers also offer advanced features such as accumulated time tracking and pre-trigger capabilities.
Siemens Timers
Siemens timers are distinguished by their flexibility and adaptability. They are programmed using ladder logic or structured text, allowing for customization and integration with other control logic elements. Siemens timers also provide a wider range of timer types, including timers with reset pulse requirements and timers with integral counters.
Conclusion
Timers play a crucial role in PLC-based control systems, enabling precise timing and synchronization of various processes. Studio 5000 offers a comprehensive set of timer instructions for Allen-Bradley PLCs, catering to a wide range of time-dependent applications. While Allen-Bradley and Siemens PLCs have different approaches to timer implementation, both systems provide effective tools for time-based control in industrial automation.
Sample Answer
Timers as Logical Devices
Timers are fundamental elements in programmable logic controllers (PLCs), serving as versatile tools for controlling time-dependent processes in industrial automation. They function as logical devices that measure and manipulate time intervals, enabling precise execution of sequences and synchronization of various operations within a control system.
Timer Implementation in Studio 5000
Studio 5000, the programming environment for Allen-Bradley PLCs, provides a comprehensive set of timer instructions that facilitate the implementation of various time-based control applications. These instructions are designed to emulate the behavior of real-world timers, incorporating features such as timers, counters, and time delays.