Apologies in advance for the lengthy post, but it's essential to provide some context. I am employed at a facility equipped with numerous Variable Frequency Drives (VFDs) in various applications, mainly within web handling and extruder machinery. The predominant VFD brands used are Allen Bradley (1336 and PF755) and Parker/SSD (690+ and 890), with power outputs ranging from 2HP to 500HP, mostly falling within the 5-20HP range. The majority of VFDs operate in a closed-loop system, utilizing either a load cell or pressure transducer for feedback. In our setup, feedback instruments are typically directly connected to the drive, with the Programmable Logic Controller (PLC) supplying speed references. An encoder is commonly installed on each drive, however, we have encountered challenges with this configuration. Issues include reliance on outdated drive hardware, software compatibility constraints, and complexities in troubleshooting due to dual control components. To address these issues, we have transitioned to using Allen Bradley PF755 drives controlled entirely via Ethernet/IP by the PLC. This setup simplifies future upgrades and maintenance, consolidates control within the PLC for easier management of Proportional-Integral-Derivative (PID) loops, and does not appear to impact process performance negatively compared to direct feedback wiring to the drive. Now, the question arises - do we still require the encoders in this setup? What benefits do they provide, considering the fast PLC scan times and Ethernet/IP communication capabilities? Furthermore, how does speed control improve in drives with fixed setpoints when utilizing a fixed/open-loop control method? These questions are crucial for optimizing our system efficiency and performance.
Having worked in the printing industry years ago, I can provide some insight on the 1336's and Eurotherm drives, which were considered top-of-the-line back in the day. The Eurotherms could also be utilized as a mini PLC with pre-built control blocks and PID options, significantly improving reaction time and process control. This made them a popular choice in the printing industry. While PLCs have advanced with fast speeds and large memory capacities, it is still essential to thoroughly study the system before incorporating them to ensure optimal performance.
The level of precision required for controlling each motor's speed/torque is essential. The encoder plays a crucial role in allowing the drive to maintain a close loop control, ensuring tight regulation of the motor's speed and torque. This level of control is particularly important in applications such as web handling, where precision is key for optimal performance.
My intuition suggests that replacing the encoders could be a risky move, as having an abundance of data can actually be beneficial if used effectively. The main challenges seem to lie in the maintenance of these systems, particularly due to their different operating systems. It would be wise to explore different options and consider whether removing the encoders is a feasible solution, especially considering the potential optimization of the system's mechanics by the PID system. Conducting an experiment in the short term is acceptable as long as risks are carefully managed and intentions are clearly communicated.
bkottaras mentioned: While my background is in the printing industry from years ago, I can provide some insight. Back then, the 1336's and Eurotherm drives were considered top-of-the-line. The Eurotherms also acted as a mini PLC with built-in blocks for control, PID's, and more. This technology greatly improved reaction time and process control, hence its widespread use in the printing industry. Despite the advancements in PLC speed and memory, I urge caution when considering a switch without thorough system study. Our journey to where we are today involved upgrading several lines with full PLC control of the drives, a successful endeavor thanks to the flexibility of plastic film compared to paper. With the assistance of a knowledgeable integrator specializing in web handling, we were able to implement innovative FBs for winders and tension control.
According to Mandel314159, the main challenges in using these drives seem to revolve around system maintenance, particularly due to their varied operating systems. This is precisely the reason why I raised this question.
Hello, great rundown of your setup! As for whether or not you need the encoders, it all comes down to your application's precision requirements, the behavior of your load, and the importance of reliable feedback. Even with a fast PLC and Ethernet/IP, an encoder can provide valuable real-time feedback that might otherwise be missed. This is especially important in applications where speed or position precision is critical, or where unexpected load changes can occur. And while Ethernet/IP communication capabilities are robust, they are not entirely devoid of potential hiccups, which could lead to control issues if relied upon solely. As for the fixed/open-loop approach, it can be favorable when you have a consistent load and don't necessarily require feedback. However, it does come with potential limitations in terms of adaptability and control precision. With fixed setpoints, you're assuming that your system will always behave the same way, which is not always the case in real-world applications. In short, yes, encoders can still add value, but it greatly depends on the specific conditions of your application.
While encoders may seem redundant in your current setup, they still have their uses, especially when it comes to precision. Even with fast PLC scan times and Ethernet/IP communication, there can be lag times or instances of packet loss, which can affect the overall system accuracy. Encoders can provide a safeguard against such instances by providing real-time and direct measurements of speed and position. That said, if your processes don't require high precision, then the encoders might be unnecessary. Regarding your question about speed control in drives with fixed setpoints, using a fixed/open-loop control method can improve responsiveness and stability in systems with predictable loads. However, it might struggle with varying or unpredictable load conditions, for which a closed-loop system would be more suited.
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Answer: - While the use of encoders may not be essential in such a setup due to fast PLC scan times and Ethernet/IP communication capabilities, they can still provide benefits like enhanced speed control accuracy and fault detection.
Answer: - Encoders can offer precise speed feedback, aiding in maintaining accurate speed control and improving overall system performance. They also assist in fault detection and troubleshooting, contributing to increased efficiency.
Answer: - Incorporating encoders in drives with fixed setpoints can enhance speed control accuracy and responsiveness, ensuring that the system maintains the desired speed levels more effectively. This can lead to improved performance and efficiency in various applications.
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