Adding new processes or expanding existing ones often involves skid-mounted equipment from original equipment manufacturers (OEMs). Skid-mounted equipment offers faster implementation times compared to traditional process systems built from scratch.
Skid-mounted equipment can provide high-quality, cost-effective solutions for utilities and primary processing functions. Integration of skid-mounted equipment can be simplified if interaction with the overall process system is minimal. In this case, only data collection or minimal interaction is required to work with the main distributed control system ( DCS ) or supervisory control and data acquisition (SCADA) system. However, seamlessly integrating skid-mounted equipment into the entire process can be challenging. Tightly integrating skid-mounted equipment into processing activities such as batching operations requires deeper levels of cohesive interaction to achieve high levels of process efficiency.
OEM skid-mounted equipment
A major challenge in integrating third-party systems into a process is the need to coordinate upstream and downstream operations and share a common operating philosophy. Typically, utility system skid-mounted equipment only needs to provide the required functionality at its design capacity. On the other hand, in larger process flows, connecting or combining OEM skid-mounted equipment requires coordination between upstream and downstream units to achieve efficient equipment utilization.
Most skid-mounted units come with their own dedicated processors and input/output (I/O) cards, typically operating independently. This means they can operate independently without anticipated upstream inputs or downstream demands. Often, the operation of the entire process must revolve around the OEM's functional characteristics. In many cases, the operational attributes of an OEM's skid-mounted unit are a direct result of system programming, rather than limitations on the unit's functionality. This means that OEM skid-mounted units are not built to be subordinate to or serve an overall process coordinator or master controller.
OEM manufacturers' independent operation of skid-mounted equipment is often a result of bundling and selling products. Changing existing operational functions poses a risk to suppliers, and they are typically reluctant to add new system functionality based on demand. Integrating skid-mounted equipment into a true batch processing system is inherently difficult because most skid-mounted equipment is not programmed according to the ISAS 88.01: Batch Control standard.
Most skid-mounted applications consist of ladder logic, initially built to provide multiple processing options. This allows an application to encompass multiple processing options. While ladder logic can be designed to follow programming standards, it does require some additional work. Overcomplicating the application by integrating multiple unused processing functions without adhering to industry-standard programming practices can make it difficult for risk-averse vendors to seamlessly integrate the system into their overall batch processing solution.
Integration for batch operations
Integrating skid-mounted equipment into the overall batch control and management system requires a clearly defined level of coordination between slave and master systems (DCS or SCADA). Simple commands to slave systems do not provide operators with a visual view of the system. If everything is normal, issuing simple master commands to slave systems is sufficient. However, when anomalies occur, it is difficult to detect and troubleshoot without accessing the equipment's local human-machine interface (HMI) to identify the problem.
This can cause operational delays, increase batch cycle times, reduce equipment utilization, and decrease overall operational efficiency. By following these four simple guidelines, you can tightly integrate the dependent OEM skid-mounted system into the main processing system:
● Allocation and operation model;
● Follow standard operating procedures;
● Define status feedback;
●Standardized communication.
The design should synchronize the two devices by defining a specific coordination method. A flexible batch processing architecture, including isolation between different functions and standardized interfaces with other functions, is crucial. This type of definition allows device entities to operate independently and promotes the reuse of basic functional code. Code reuse reduces overall engineering time and minimizes the possibility of human error.
1. Allocation and Operation Model
Without clearly defined boundaries, operating models for remote equipment can be tricky. If control variables have been remotely issued from the overall recipe, can operators modify the equipment locally? Should the recipe enter a hold state when a specific operating state changes? These are just a few questions to consider when integrating remote equipment. Interface rules and operating principles between the master and slave systems should be clearly defined to provide a continuous and unified interface between the two systems.
2. Follow standard operating procedures
Standardized operating conditions allow for a mechanism to handle the challenging aspects of batch operations, i.e., abnormal conditions. Abnormal conditions can be defined as events that occur outside the normal or expected behavior of a process. Responding to, handling, and recovering from these conditions are key elements of batch production. Abnormal handling is important not only for process safety but also for product quality and is crucial for achieving high levels of operational efficiency. Handling abnormal conditions can account for up to 70% of programming workload and must be considered a goal in the batch processing design process.
3. Define state feedback
Status feedback is a crucial part of effective operation between two systems. This information should be constructed and defined for modes, operating states, and error conditions. Standard modes and states should be universal across all devices, but abnormal operating conditions vary for each device. Specific fault feedback from slave or remote systems can provide a visual indication of the current operating condition. Fault status can also be used to identify preventative measures to improve equipment utilization and overall system efficiency.
4. Standardized communication
Communication between systems can be achieved very efficiently by specifying a single integer value. Communication can be very simple, using a single word to command the slave system and providing a status word from the slave system. Common command status follows operational patterns and is frequently used.
However, due to the overall recipe settings in the main system, additional parameters or system variables may need to be written into the slave programmable logic controller (PLC). Standardization of communication with remote or third-party devices makes the control system easier to maintain and expand throughout its lifecycle. The development of remote interface communication standards must be designed to be broad enough to cover a wide range of application types.
Interaction Standardization
Integrating slave or remote systems can be challenging, but standardized interfaces make processes easier to manage. Two of the four guidelines mentioned above are explicitly defined in the ISAS 88.01 standard. Communication packets and status feedback between systems can be defined to cover all third-party solutions. A common interface design promotes consistent and coordinated operation throughout the system, making it easy to maintain and extend.
Common interfaces should be documented in design deliverables and provided to OEMs as user requirement specifications to ensure compliance with standards. This will ensure that remote system programming aligns with expected operations. Standardizing interactions to include abnormal operating conditions provides a system that is easier to operate and maintain, thereby achieving a high level of operational efficiency.
Disclaimer: This article is a reprint. If it involves copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
