Hello, I am seeking advice on how to accumulate operating hours based on a simple XIC condition. I am considering using a RTO with either a 60000 or 3,600,000 preset, along with 1 or 2 CTU. The equipment may be in operation for up to 12 non-stop months. I also aim to limit the number of operations on a breaker. My concern is ensuring that the count/value is not lost during a full PLC download. While it is typically recommended to make a note of the actual value and re-enter it post-download, this may not always be feasible. Is there an alternative method to prevent data loss? In a previous experience with a different brand, I utilized a secondary PLC on the network at a "higher level" to retain values. However, this solution seems excessive for a simple time counter. I have a similar setup here with a PLC at a higher level and would prefer a less complex approach. Additionally, there is a standalone InTouch HMI on the system. Is there a way to utilize this for data retention? Any suggestions would be greatly appreciated.
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Utilize the least significant bit of the PLC clock's seconds DINT and add an ONS instruction to trigger an ADD operation, incrementing the "Total_Process_Seconds" DINT tag value by 1. This tag can be employed to calculate total operation time in minutes and hours using the DIV function, while the MOD function is beneficial for recurring process intervals. It is essential for the DINT tag to retain its value when the PLC is restarted, ensuring a continuous operation with battery or capacitor backup. Reset the "Total_Process_Seconds" tag at the commencement of each operation. Consider creating a "One_Second_Trigger" bit tag following the ONS instruction for a convenient 1-second timer in your program, substituting the need for TON, TOF, or RTO instructions. Reserve these latter instructions for tasks demanding greater time precision with a resolution below 1 second.
To enhance the functionality and ensure data retention of a PLC clock's seconds DINT, utilize the 0 bit and implement an ONS instruction followed by an ADD operation involving the "Total_Process_Seconds" DINT tag. This tag facilitates the computation of total operation minutes and hours using the DIV function, while the MOD function aids in managing reoccurring intervals within a process. It is crucial for the DINT tag to maintain its value even when the PLC loses power and restarts, as long as there is battery or capacitor backup in place. Reset the "Total_Process_Seconds" tag at the start of each operation to ensure accurate calculations. Consider creating a "One_Second_Trigger" bit tag for simple 1-second timer accumulators instead of relying on TON, TOF, or RTO instructions. Reserve these latter instructions for tasks demanding greater time precision below 1 second. Remember that when downloading changes, the stored value could potentially be outdated, spanning hours, days, or even weeks.
Robertmee noted that the solution provided does not meet the original poster's needs of preserving the value during a download. The data accumulated in the provided example may be outdated by hours, days, or weeks in the downloaded version. It appears that using an external storage option, like an HMI or another PLC, may be the ideal solution unless a PLC is utilized that segregates register or tag memory from the logic. A PLC like the IDEC FC6A can retain register values post downloading full logic updates.
When reviewing DaDaDadeo's comment, there was a recommendation to consider utilizing external storage like an HMI or another PLC if the PLC being used doesn't separate register or tag memory from logic. For example, the IDEC FC6A PLC retains register values after full logic updates. It's likely that Rockwell PLCs are being used, as indicated by the XIC, CTU, and RTO mnemonics. Rockwell offers a tool that allows for logic downloads while preserving tag values.
Using a secondary PLC to retain values might indeed be a little overkill for a simple time counter. Instead, you can try what's called an 'Indexed Data Table'. This is a data structure in PLC that can be used to store values despite a full PLC download. Since your HMI already has access to the PLC, it can call and write data back to the indexed data table whenever necessary, say, right before a PLC download. This should address your concern about data retention. Also, don't forget to factor in edge cases such as power outages or abrupt system shutdowns, which might require manual data back-ups.
This is certainly a concern many of us have faced before. In your case, you might want to consider using non-volatile memory for storing your counter value. You could write to an area of the PLC's memory that isn't affected by downloads. This would allow the counter to retain its value even during a full download, eliminating the need for manual re-entry. As for your InTouch HMI, it also offers write capabilities and you can use these to store your counter. An example would be to set up a script that writes the PLC's counter value to the HMI at regular intervals, and then another script that writes back to the PLC from the HMI when needed, acting as a sort of backup. The specifics will depend largely on your exact PLC and HMI models, so you might need to deep dive into the manuals to see what's possible. However, these suggestions should give you a good starting point.
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Answer: - One method to prevent data loss during a full PLC download is to utilize a secondary PLC on the network at a "higher level" to retain values. However, this approach may be considered excessive for a simple time counter. Alternatively, consider using a standalone InTouch HMI on the system for data retention.
Answer: - When accumulating operating hours based on a simple XIC condition, you can consider using a RTO with preset values such as 60000 or 3,600,000, along with 1 or 2 CTU. Additionally, aim to limit the number of operations on a breaker for efficient tracking.
Answer: - To ensure that the count/value of operating hours is not lost during extended equipment operation, it is recommended to make a note of the actual value and re-enter it post-download after a full PLC download. If this method is not feasible, explore alternative solutions such as utilizing a secondary PLC or leveraging a standalone InTouch HMI for data retention.
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