Hello everyone! I am preparing to incorporate a second identical HMI into a project. This new HMI will essentially mirror the functionality of the first one. Our equipment can be operated from either HMI, based on the customer's requirements for the day. It is important to note that only one HMI can be used at a time to control the unit, avoiding any conflicts. Both HMIs will display the same screen simultaneously by monitoring an integer value in the PLC. One concern I have is regarding pushbuttons on the screens triggering actions in the PLC. If a button is pressed on one HMI while it is not pressed on the other, will this create a conflict in the PLC? I am using Automation Direct EA9 HMI and a MicroLogix 1400 PLC, with one HMI connected via Ethernet and the other through RS-232. I believe that as long as the bit in the PLC controlled by the pushbutton changes state as intended, even momentarily, there should not be any issues. However, I would appreciate any advice or insights on managing potential conflicts in this setup. Thank you.
If one button is pressed on one HMI while the same button on the other HMI is not pressed, it may create a conflict in the PLC. However, there is no need to be concerned about this. When you touch a momentary pushbutton on the HMI screen, a value of 1 is written to the corresponding bit in the PLC. This value is written only once. When you release the button on the HMI screen, a value of zero is written to the PLC bit, also only once.
According to Steve, the communication server functions based on state changes and updates values accordingly. One important consideration for duplicated HMIs is the potential security issues that may arise if only one HMI is logged in, as well as any alarm acknowledgment discrepancies between the two HMIs.
In situations where multiple HMI units are used, a common practice is to implement a 'Take Control' feature. This can be achieved through an external selector switch or HMI buttons. The manual controls are typically grouped on specific pages within the HMI, with access restricted to the HMI currently in control. This measure is crucial in preventing safety incidents, such as the accidental triggering of actuators by unauthorized personnel. A key requirement is for operators to release control after use, allowing others to take over from different locations. A popular choice is to use illuminated selector switches that indicate control status. While there may be instances where operators forget to release control initially, the system typically operates as intended after a short adjustment period. This approach ensures smooth and safe machine operation. Regards
From your description, it sounds like you've got a solid grasp of the situation. The key is indeed ensuring the state changes in the PLC are well-coordinated. To manage conflicts in your dual HMI set up, you could consider implementing features such as a HMI selection lock, which will prevent unwanted changes from the idle HMI. Also, it's important to ensure both HMIs are updated evenly and simultaneously, especially when setpoints are changed. Use the RSlogix software to monitor how actions on one HMI are affecting the PLC and the other HMI. This might help you identify and resolve any potential conflicts down the line.
Your setup sounds technically sound. As you suggested, as long as the PLC state changes as intended, there should be no conflict. It might be considered for you to implement a mechanism within the PLC program to identify which HMI initiated the state change. That way, you can retain direct control over operation-based conflict resolution. Also, you should consider the latency of the respective communication channels for both HMIs. A sync issue might arise if one HMI communicates significantly faster with the PLC than the other one.
It sounds like you have a solid plan in place for your dual HMI setup! Since you're using a master/slave configuration to manage which HMI controls the PLC at any given time, you might want to implement a locking mechanism in your PLC logic. This would ensure that only one HMI can send commands to the PLC at a time, effectively preventing any unwanted conflicts. Additionally, consider using a status indicator to inform users which HMI is active, helping to avoid confusion when someone tries to make adjustments. Overall, keeping your control logic clear and streamlined will definitely help in avoiding any unexpected behavior! Good luck with your project!
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Answer: Answer: To incorporate a second HMI into your project, ensure both HMIs mirror the same functionality and can control the equipment based on customer requirements. Use a method to monitor an integer value in the PLC to synchronize the screens.
Answer: Answer: To prevent conflicts, ensure only one HMI can control the unit at a time. Monitor the pushbutton states in the PLC to manage potential conflicts that may arise when one HMI triggers actions that the other HMI does not.
Answer: Answer: Pressing a button on one HMI should not create conflicts in the PLC as long as the bit controlled by the pushbutton changes state as intended. Monitor and synchronize the states of the pushbuttons between HMIs to avoid potential conflicts.
Answer: Answer: The thread mentions using Automation Direct EA9 HMI and a MicroLogix 1400 PLC, with one HMI connected via Ethernet and the other through RS-232. Ensure compatibility between the HMIs and the PLC to effectively integrate a second HMI for remote operation.
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