JZerb inquired whether you organize all your HMI (Human-Machine Interface) referenced tags in a specific manner within your PLC (Programmable Logic Controller) system. For instance, during programming with RSLogix 500, you might categorize all digital push buttons as B3:15. I remember reading somewhere that this method holds certain advantages, although I can't recall the specifics.
I believe adopting a systematic approach is a great idea for maintaining organization. Regardless of the method you select, it’s crucial to remain consistent. Future operators or technicians working on the system after its commissioning will benefit significantly from this clarity, making their tasks easier. I always keep in mind the next person responsible for maintaining the machinery after I'm finished, striving to write clear and understandable code so they won’t need to reach out to me in the middle of the night for support.
JZerb inquired: Do you consistently organize all your HMI-referenced tags using a specific naming convention within the PLC? For instance, when programming in RSLogix 500, we might place all digital push button inputs under the address B3:15. I remember coming across information suggesting this approach has its advantages, but I can't recall the specifics. Click to expand...
In our setup with Studio 5000, we adopt a similar strategy by prefixing the majority of our HMI tags with "hmi_". Although this practice may not always optimize PLC-HMI network communications, it offers significant benefits when assessing tags. If you find a tag that isn’t actively toggled on or off in the PLC, it signals that it might be managed elsewhere in the system, indicating it’s a candidate for potential removal.
JZerb inquired whether you maintain a consistent naming convention for your HMI (Human-Machine Interface) referenced tags within your PLC (Programmable Logic Controller). For instance, when programming with RSLogix 500, all digital push button tags for the HMI could be organized under B3:15. I seem to recall learning that this approach has its advantages, although I'm not quite sure of the specific reasons.
To elaborate, HMIs typically read entire words rather than individual bits. If you utilize single bits across multiple words, you may inadvertently increase network traffic, which can hinder performance. It's essential to streamline your tag organization to optimize communication and efficiency within your automation system.
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Every professional has their own approach to writing code. Here’s mine for effective programming. First, thoroughly review the specifications multiple times. Clarify the difference between "shall" and "should" within these specs. Copy the specifications, highlighting key aspects such as PLC parts, limitations, travel parameters, and force requirements.
Next, document the operational sequence clearly—focus on the steps rather than personal pronouns like "I." Review and revise your notes until they are coherent. Incorporate input/output (I/O) details, and figure out the necessary subroutines. Write your code in a clear, step-by-step format.
Always keep your end-users in mind; after all, your customer is paramount. The goal is to facilitate maintenance. Consider what the maintenance team is accustomed to and which PLC they are familiar with. Do they have experience with sequencers, GRAFCET programming, step logic, function blocks, or structured text?
When you write code that aligns with their understanding, maintenance will find it easier to troubleshoot and work with the machinery, ultimately leading to smooth operations. This could inspire them to recommend your services for future projects.
Conversely, if you create code that only you understand, the machinery may fail to operate effectively, as maintenance personnel will struggle to decode the program. This situation can lead to frustrations: the project manager faces complaints, your supervisor gets pressured, and you end up having to rewrite the code. In response to such issues, future projects may include stipulations requiring maintenance approval of the program before final payment. A colleague of mine learned this lesson the hard way.
James
JZerb mentioned they are eager to learn some effective strategies for staying organized and focused when developing a program from the ground up. Typically, they begin by defining the project scope, documenting the input/output requirements, alarms, and occasionally jotting down ideas on a scratch pad before transitioning to Excel for more detailed organization. However, they believe there are more innovative techniques out there and hope others will share their insights.
Here are some practices I usually follow when working with Rockwell systems. It has been a while since I’ve worked with Modicon/Schneider, Telemecanique, or PLC Direct. Here are a few key strategies I use:
- I prefer using integer files instead of boolean files for HMI tags.
- Each HMI section has its own dedicated READ and WRITE files for both digital and analog signals.
- Alarm management involves maintaining separate files, such as raw alarms, masked alarms, new alarms, and acknowledged alarms, for each HMI area.
- For motor control, I design standard rung patterns for small PLCs and create a subroutine for larger PLC applications. I favor using Advanced Organizational Instructions (AOIs) over subroutines when a continuous process isn't required, as AOI edits necessitate downloads.
- Gate logic parallels motor control logic, utilizing standard rungs and subroutines for more complex PLC systems.
- Motors and gates each have a 16-bit integer dedicated to status and another for alarms, allowing efficient data transfer to the HMI by grouping necessary status bits together. Additionally, having a status rung that displays all inputs, outputs, and internal signals can be invaluable for troubleshooting.
This outline assumes dedicated maintenance personnel are available, as teaching data structures to staff lacking a computer science background can be quite challenging. Despite the complexity of masks, binary operations, and subroutines, I find that they significantly ease my workflow.
However, it is essential to strike a balance, especially considering the possibility of receiving emergency calls at unexpected hours. Opting for hard-coded logic instead of subroutines can complicate the resolution of widespread issues, such as improper wiring of limit switches or emergency stops.
Minimizing downtime is crucial, making swift commissioning paramount. This often leads to debouncing inputs in separate subroutines and utilizing bits for logical operations. Keeping consistent organization of inputs and motor logic can be beneficial, but it may confuse maintenance staff if they cannot easily locate connections.
A good rule of thumb is to plan for an additional 25% capacity. It's common to modify systems post-installation, and with each removal, expect two to three new components to be added. Thus, spare I/O should be allocated in each cabinet, along with reserve space on DIN rails for power supplies and distribution terminal blocks.
I advocate for a top-down design philosophy combined with bottom-up implementation. It is advantageous to group similar components together, such as valves, motors, and process areas. Maintaining a systematic approach with asset numbers or location-based identifiers enhances searchability within the system.
When documenting rung comments on status or debug rungs, include relevant orders—like asset numbers or loop identifiers—and a selection of keywords for efficient searching, such as pump, belt, screw, drag, valve, butterfly, knife, and ball. Having conversations with maintenance teams can provide insight into how they refer to equipment and help avoid brand name confusion by using generic terms (e.g., "drag conveyor" instead of brand names like Redlar).
For recipe or sequencing tasks, consider separating the logic for each step—perhaps through subroutines or a dedicated section of rungs—while integrating control actions (such as start, stop, open, close) with corresponding equipment logic. This allows for quick identification, making it easier to see that, for instance, "sequence 7, step 4" activates the bucket elevator within the relevant rung group.
That concludes my thoughts on this matter.
I adhere to the principles outlined in ISA-88, as its physical and procedural models are applicable to virtually any type of process, whether it’s a batch system or otherwise. By utilizing these models, I can decompose the project into smaller, manageable tasks. This approach helps me remain organized and focused, ultimately leading to the creation of a Work Breakdown Structure (WBS), a key concept in Project Management.
To document the entire process in accordance with the physical and procedural models, I use Excel to outline devices, develop an index of required process sequences, and maintain clarity. Before engaging with the PLC, I employ GRAFCET and flow diagrams to “design on paper,” ensuring that the general process sequencing is in harmony with the equipment and procedures I’ve identified earlier. This preliminary exercise provides insight into areas where the logic will be straightforward or more complex.
Once this foundational work is complete, I proceed with programming. It’s important to note that all these preparatory steps align with modular programming principles, facilitating the application of our PLC/SCADA standards. This means that once everything is documented, translating it into code is a streamlined process. The WBS serves as my tool for tracking progress throughout the project.
Finally, I engage in a series of testing phases: manual control, semi-automatic control, and fully automatic control. This method allows me to validate the logic function against the functional design specification, ensuring that I am on the right track and primed for Factory Acceptance Testing (FAT) with the client.
My workflow can be succinctly summarized in the following steps:
1. Develop a Work Breakdown Structure (WBS)
2. Document process and equipment details as they pertain to ISA-88 models
3. Create a Functional Specification Document
4. Proceed with programming
5. Conduct testing phases
This structured approach not only enhances efficiency but also ensures project success in line with industry standards.