Hello everyone, I'm a newcomer to plctalk and this is my first post. I'm currently working on programming a micrologix 1400 plc using RS Logix 500. The goal of the project is to operate 8 boilers, with 2 as the primary leads and the remaining 6 as available lags to be activated if one of the leads falls below a setpoint. The lags will cycle off once they reach a specific setpoint. Additionally, all 8 boilers need to undergo a fault sequence while functioning as leads and lags. The lead-lag logic involves calling on lags in sequence if either lead 1 or lead 2 fall below the setpoint. I've been struggling to find a solution and it feels like I'm going in circles. Any assistance would be greatly appreciated. Thank you!
There are two primary approaches when it comes to boiler operation: 1. The first approach involves a modulating boiler which adjusts its firing rate based on demand. When the modulating boiler reaches a high firing rate, it triggers the activation of the first lag boiler. Once the modulating boiler reaches its maximum firing rate, it switches roles with the first lag boiler. 2. The second approach entails all boilers adjusting their firing rates in response to demand changes. When the firing rate of the boilers reaches a certain level, the next lag boiler is added. On the other hand, if the firing rate drops below a certain threshold, one boiler is removed from operation. It is important to consider the size uniformity of the boilers and whether a demand sensor is in place to detect changes, or if header pressure maintenance is the primary focus.
Thank you, Steve, for your response regarding the boiler system. Each boiler is designed to maintain a consistent header pressure and operates at the same firing rate based on this pressure. I monitor the load output of each boiler and make lag calls based on specific setpoints. I have developed 8 different boiler sequencing options, wherein boilers 1-8 can be in various lead and lag positions. However, the challenge arises when a boiler in alarm position is cycled into a lead position, causing the logic to overlook available boilers. For example, if boilers 1 and 2 are designated as lead boilers but are in alarm state when cycled into those positions, they will remain there instead of searching for the next available boiler. This issue needs to be addressed in order to ensure smooth operation of the system and prevent unnecessary downtime.
While I may not be able to offer assistance, you may find the information shared by Ron in this thread helpful: http://www.plctalk.net/qanda/showthread.php?t=9499&page=5. In case the link doesn't work, the post can be found at #61 in the same thread: http://www.plctalk.net/qanda/showthread.php?t=9499. Hope this helps.
One helpful tip is to consider using letters instead of numbers to identify your boilers. This will make it easier to maintain a priority table for your boilers. When the header pressure falls below the setpoint for a certain period, it's important to prompt the next boiler in line to start. Using letters, like naming a boiler "C" as opposed to number, can prevent confusion on the priority list. In terms of addressing boiler alarms, if a boiler goes into alarm while supplying steam to the header, the next boiler in line should be activated immediately to prevent pressure drops. Don't wait for the pressure to decrease. PS: HeroControlsInc, please check your private messages for contact details for a possible discussion.
Consider organizing the logic for each boiler in its own Logic Block. One potential approach is to use two FIFO stacks: one for StandbyBoilers (with six positions) and another for LeadBoilers (with two positions). These variables have indirect references pointing to the appropriate control Block when required. While my explanation may not be perfect, I envision this setup working effectively.
Welcome to plctalk! Don't worry, we've all had experiences where it felt like we were running in circles trying to get a program to work. For your project, you might consider using ladder logic to create a simple sequence for your boilers; starting with the two lead boilers and systematically bringing the lag boilers online if the leads fall below setpoint. For fault sequences, you might consider using a parallel rung to monitor each boiler for faults. If a fault is detected, this could trigger either an alarm or another fail-safe response you decide to integrate. Still, it's crucial to determine what precisely these 'faults' might be, are we talking about temperature exceedance or operational abnormalities like pressure drops? That would provide a more tailored response. Best of luck with your project!
Welcome to the forum, it's great to have you participating! Your project sounds quite complex but really interesting. One approach for lead-lag logic might include setting up an array in your PLC program to monitor the status of each boiler. You could use this to track whether a boiler is functioning as a lead or a lag, and make the adjustments as necessary. However, always remember to handle your faults with priority, these should be able to override any typical sequences. All the best with your project, and don't hesitate to ask if you have further questions.
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Answer: Answer: To program a lead-lag system for 8 boilers using a MicroLogix 1400 PLC, you can utilize RS Logix 500 to set up the necessary logic. The system should involve selecting 2 boilers as primary leads and the remaining 6 as lags to be activated based on setpoints, with cycling off once the setpoint is reached.
Answer: Answer: The key concept of a lead-lag control system for boilers is to have primary lead boilers operating first and then activating lag boilers based on specific conditions, such as if a lead boiler falls below a setpoint. This ensures efficiency and redundancy in boiler operation.
Answer: Answer: When facing challenges in programming lead-lag logic for boilers using a MicroLogix 1400 PLC, it can be helpful to break down the problem into smaller steps, review your logic for any errors, and seek assistance from online forums or PLC experts for guidance.
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