Automation Device Variable Sampling Decoupling
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Solution Overview
Problem
OPC UA servers on low-performance automation devices face resource bottlenecks and latency issues due to the strict client-server model, where each read and write request requires variable retrieval and response, leading to inefficiencies, especially in non-deterministic processes.
Innovation Solution
The automation device specifies a time period between read and write requests for the same variable, allowing for sampling times to be set independently of client requests, enabling access to variables in the server's address space at predetermined times, thereby decoupling client requests from server access and reducing resource utilization and latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the OPC UA server retrieves variables from the address space for each client request, then the client receives accurate variable values, but the server experiences high resource utilization and latency
Solution Approach 1:
The server performs preliminary actions by retrieving variables from the address space at predetermined sampling times before client requests arrive. This allows the server to pre-process and store variable values, so when a client request comes in, the server can quickly return pre-retrieved values without performing the full retrieval operation at request time, thus reducing latency while maintaining accuracy.
Solution Approach 2:
The server implements periodic action by retrieving variables at predetermined sampling times rather than on every client request. This periodic retrieval strategy reduces the frequency of address space access, lowering resource utilization while still providing timely updates to clients based on the sampling schedule.
2Reliability
If the OPC UA server follows the strict client-server model and processes each request synchronously, then communication protocol compliance is maintained, but resource bottlenecks occur on low-performance devices
Solution Approach 1:
The server performs preliminary variable retrieval and stores results before client requests arrive. This pre-processing reduces the computational burden during actual request handling, making the system more suitable for low-performance devices while maintaining protocol compliance through proper response formatting.
Solution Approach 2:
The server acts as an intermediary by maintaining its own internal cache of variable values from the address space, rather than directly querying external devices for every client request. This intermediary cache layer reduces the complexity and resource requirements of each individual request processing cycle.
3Loss of time
If the server retrieves variables at the time of each client request, then up-to-date values are provided, but significant latency occurs in the automation process
Solution Approach 1:
The server performs preliminary variable retrieval at predetermined sampling times before client requests arrive. This pre-fetching strategy significantly reduces the time required to process client requests, as the variable values are already retrieved and stored in memory, eliminating the need for time-consuming address space access at request time.
Solution Approach 2:
The server implements periodic variable retrieval at optimized sampling times, balancing between providing up-to-date values and minimizing processing time. This periodic approach ensures variables are updated frequently enough to maintain freshness while avoiding excessive retrieval operations that would increase latency.
4Manufacturing precision
If the OPC UA server accesses variables in the address space for every read/write request, then complete data accuracy is ensured, but the load on automation devices increases
Solution Approach 1:
The server accesses variables periodically at predetermined sampling times rather than on every client request. This reduces the frequency of address space access and external device queries, significantly lowering energy consumption while maintaining sufficient data accuracy for automation processes through optimized sampling intervals.
Solution Approach 2:
The server creates copies of variable values from the address space and stores them locally in its memory. Instead of repeatedly accessing the original address space for every client request, the server serves copies from its cache, reducing the load on the automation device and energy consumption while providing clients with accurate variable values.
Data Source
AI summary
An automation device for process automation, with a server containing one or more process automation variables, wherein the server is configured to receive read and/or write requests from a client in communication with the automation device for at least one variable. The automation device adapted to: specify the time period between two read requests for the same read request variable and/or between two write requests for the same write request variable; specify a sampling time for the read or write request variable as a function of the specified time period; and enable read access to the read request variable in the address space of the server at the respective sampling time, independently of future read requests and/or to prepare write access to the write request variable in the address space of the server at the respective sampling time, independent of the previous write request.