Decoding Mitsubishi FX3 Programming: Understanding K9999999 Value, C251 Assignments, and Press Position Transfer

Question:

I have been decoding a program for a press, delving deep into it using the manual to understand the instructions. One question that has arisen is the purpose of the K9999999 value in the rung assigned to C251 with an A/B encoder. Does it signify a maximum count value or set C251 to 9999999 after the scan? Another aspect that is perplexing is the rung resetting C251 to zero on the first scan after activating Run mode (M8000), only for it to be changed back. Additionally, a rung further down involves transferring the press position readout (D200) to C251 every scan. The manual's explanations have been somewhat vague, especially regarding the OTE instruction and reset functions working together.

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The initial step in utilizing these counters (C235>) is to establish the maximum value. This value dictates when the output contact will be activated once the counter reaches it. Typically used for high-speed A/B count functions, these counters are hardware-tied to X0-X7 inputs. While it is possible to manually set a counter to a specific value, it is recommended to refer to the user manual for precise instructions. Resetting the counter will return it to its original value. The purpose of this process may rely on additional logic, but it appears to be related to encoder functionality. Explore the Mitsubishi Electric PLC FX manual for further details: [link to the manual]. If you already have the manual, focus on understanding the reset function and setting the maximum count, rather than questioning the current counter value adjustment.

To maximize efficiency, the counter value has been set to K9999999 as a precautionary measure, assuming it will not exceed this value. This setting is commonly used for measuring distances from linear incremental encoders or similar devices. The C251 counter is a versatile 2-phase, 2-count input system that accurately tracks both up and down counts.

It is unusual for counters to only track rising edge (false-to-true) transitions within their input rung. After the reset on M8002 during the first scan, the subsequent M8000 (RUN - always set to 1 in PLC Run mode) will cause C251 to count up to 1*. From there, it should not count again since M8000 always maintains a value of 1 and cannot transition from 0 to 1 again. This is assuming the reset function clears the "last scan's input rung state," making M8000 appear as a rising edge in the next scan cycle.

In PLC programming, the initial rung of counters like C235 sets the maximum value for the counter output contact to activate. Typically used for high-speed counting functions with encoders connected to X0-X7, it is possible to adjust the counter value based on the manual instructions provided. The reset function is used to clear the current counter value, which may be related to other logical operations, especially when dealing with encoders. The manual linked provides detailed information on setting up counters for specific functions. It seems that the counter value is set high, such as K9999999, to measure distance using an incremental encoder. C251, functioning as a 2-phase, 2-count input counter, is used to accumulate and reset values for rotational operations. When discussing the counting process, it is important to note that counters typically count rising edge transitions of their input rung. The use of DHSCR to reset the count at 360 counts ensures that the incremental count acts as an absolute value for angle measurement, especially in press operations. Overall, setting up HSC functions in Mitsubishi PLC involves activating internal structures for high-speed counting with encoders. This setup differs from other systems, like Allen Bradley, where options are toggled in a menu. The reset function in the Mitsubishi PLC clears stored values, providing a fresh start for counting operations within the processor.

The internal workings of the C251 are structured in a specific manner. Opting for a different option will result in a new hardware assignment and utilization for counting purposes.

From what you've described, it sounds like K9999999 could be acting as a place holder for the maximum possible value, making sure the encoder wouldn't go beyond this count value. However, since every press machine differs, it might still be best to confirm this with the vendor or manufacturer who would know better. As for C251, initially resetting to zero at Run mode, then being changed again, sounds like a boot-up sequence - sort of like a two-step verification. It checks basic functions (like resetting) before continuing operation. Transferring the press position readout (D200) to C251, is likely for real-time tracking and control. The OTE (Output Energize) instruction typically operates as an "on-off switch," possibly acting here as a trigger to start the described processes. But, since this is only one interpretation and PLC programming can be complex, I would caution against making any changes based on just this information. You might want to reach out to an expert or a PLC forum for specifics related to your press program code.

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Frequently Asked Questions (FAQ)

FAQ: 1. What is the significance of the K9999999 value in the rung assigned to C251 with an A/B encoder?

Answer: - The K9999999 value in the rung assigned to C251 typically signifies either a maximum count value or setting C251 to 9999999 after the scan.

FAQ: 2. Why does the rung reset C251 to zero on the first scan after activating Run mode (M8000) and then change back?

Answer: - The rung resetting C251 to zero on the first scan after activating Run mode may be part of the programming logic to ensure proper initialization before the actual operation.

FAQ: 3. How does the rung involving transferring the press position readout (D200) to C251 every scan work?

Answer: - The rung transferring the press position readout (D200) to C251 every scan is likely designed to continuously update C251 with the latest press position information for real-time monitoring or control purposes.

FAQ: 4. Can you explain how the OTE instruction and reset functions work together in the context of the Mitsubishi FX3 programming manual?

Answer: - The manual's explanations regarding the OTE instruction and reset functions working together may be vague, but typically, the OTE instruction is used to enable or disable an output based on a condition, while reset functions are used to initialize or clear specific variables or memory locations within the program.

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