Do you have a seal-in circuit that seals in the OTE pump in the auto mode, with a parallel branch referencing the same tag? This is a common setup, but I have encountered a problem where the motor switches from auto to manual on power cycle. This may be due to all outputs being set to zero until after the first scan, causing the seal-in condition to be zero as well. Consider MOVING a 1 into this after the first scan to resolve the issue. Have you experienced something similar?
When it comes to programming basics, it's important to avoid using seals in to ensure retention after a power cycle. Instead, utilize two rungs: Xic auto PB OTL AutoXic man PB OTU Auto. By following this method, the automation system will maintain a state of 1 during power cycles.
Consider utilizing a first scan set to true or employing OTL/OTU, as recommended by robertmee. To understand why OTL/OTU is effective while OTE with a hold in coil is not, research the prescan operation for further insights.
I haven't worked with RW in a while, but in many Programmable Logic Controllers (PLCs), it is common to utilize retain bits that preserve their status even when the system is stopped or powered off.
Avoid using latches to control physical outputs as it can be dangerous in case of power outages or emergency stops. Overusing latches and OTL/OTU instructions in a program can make debugging a frustrating task for maintenance personnel. It is recommended to use caution and consider safety implications when designing control systems for machinery or equipment.
In response to a query by jstolaruk, it is advised not to use latches for controlling physical outputs as it can pose a safety risk during power outages or emergency stop situations. Overusing latches and OTL/OTU instructions can make debugging complex for maintenance personnel. While OTL/OTU are suitable for persistent mode control in Auto mode, caution is necessary for critical equipment to ensure safe operation after power disruptions. Agitators in remote Tank farms, heating control loops, lubrication pump circuits, etc., should restart immediately upon power restoration with Auto mode persistence. It is recommended to organize OTL/OTU pairs within a few rungs to streamline programming and avoid unnecessary duplication.
I've encountered a similar issue in the past. It does seem that the seal-in condition would be reset to zero during the power cycle. Your suggestion of using a MOV command to move a 1 into the condition after the first scan seems like a viable solution, and this is actually a workaround I've used myself. It's also worth considering the use of an UPS- Uninterruptible Power Supply to prevent these types of power cycle interruptions. What PLC are you using by the way? This might also have an impact on how to best handle this issue.
Yes, I have definitely encountered something similar in the past. I resolved it by implementing a sort of "memory" feature that initiates on the first cycle. Essentially, I coded it so that the initial state (auto or manual) is stored within the system during the power off sequence. This ensured that the previous state is remembered and reset immediately after power-on, ruling out any chances of a default reset. It may take some time to program depending on your PLC model, but it was a successful fix for me.
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Answer: 1. Why does the motor switch from auto to manual mode on power cycle in a seal-in circuit setup for OTE pump? - The issue may arise due to all outputs being set to zero until after the first scan, causing the seal-in condition to be zero as well. Moving a 1 into this after the first scan can resolve the issue.
Answer: - Yes, it is a common setup to have a seal-in circuit for the OTE pump in auto mode with a parallel branch referencing the same tag.
Answer: - Moving a 1 into the seal-in condition after the first scan can help prevent the motor from switching modes during power cycles.
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