Do PCS 7 ES Tags or DB Tags Increase CPU Cycle Time When Used for WinCC Buttons?
Using a PCS 7 Engineering System (ES) process tag instead of a direct DB-based tag does not, by itself, determine the controller scan time. CPU cycle time depends on the automation program and its execution load; WinCC display refresh is separately affected by tag acquisition/trigger cycles, number of requested values and communication response. For button color changes, configure the needed tag with an appropriate WinCC trigger/update cycle and measure the controller and Runtime under the actual project load.
Table of Contents
- Separate AS program scan from WinCC tag acquisition
- What an ES process tag changes
- Choose an appropriate WinCC trigger cycle
- Factors that affect observed performance
- Configuration and test approach
- Expected result and verification
- Version and scope limits
- Verification
- Limitations and Operational Precautions
- Engineer FAQ
- Technical References
- Related Articles
- Related Tags
Separate AS program scan from WinCC tag acquisition
The PLC executes its control program in configured tasks/cycles. WinCC reads external process values according to configured acquisition or trigger behavior, then updates the Runtime object. These operations are related through communication but are not the same timing setting. The source answer's statement that WinCC refreshes tags by a trigger cycle addresses HMI update timing, not the full cause of AS cycle time.
What an ES process tag changes
In PCS 7, ES engineering supports process tags and their connections to AS block I/Os and the OS. Using an ES-managed symbolic process tag may improve project consistency and maintainability compared with manually referencing a DB address, but the source does not identify the exact tag type or engineering path meant by “ES variables.” Do not assume symbolic versus absolute addressing alone proves a CPU timing difference.
Choose an appropriate WinCC trigger cycle
The button's displayed color can only reflect the tag value available to WinCC. Confirm the selected tag trigger/acquisition cycle for the relevant WinCC version and picture. Siemens' WinCC V8.1 manual notes that cyclical trigger cycle time affects project performance and recommends sub-second triggering only when rapidly changing values need to be queried. This is a WinCC V8.1 statement; verify the installed release's cycle options and limits.
Factors that affect observed performance
Runtime response can be affected by the number of values requested, how often they are read, the number of animated objects, configured trigger cycles, communication latency and the AS's existing execution/communication load. These factors can influence update delay or system loading without making the tag's storage area the sole determinant. The ticket provides no processor, program-cycle or communication measurements, so a numeric impact cannot be predicted.
Configuration and test approach
- Identify what the project means by “ES variable” and “DB” and compare the actual WinCC tags, AS addresses, types and connections.
- Confirm both candidate tags read the intended signal and that the button's dynamic color property uses the correct tag.
- Review the selected WinCC trigger/acquisition cycle; choose a cycle appropriate to how quickly the visual change must be observed and the project's performance constraints.
- Compare AS cycle-time diagnostics and Runtime responsiveness before and after changing only the relevant tag source or update cycle, using the project's approved test process.
- If AS scan time changes, investigate program execution, communication load and other concurrent changes rather than attributing the difference to “ES” versus “DB” without a controlled comparison.
Expected result and verification
The button should update according to the WinCC tag value and configured trigger cycle. Verify that the color reflects the intended tag state and that the actual AS cycle diagnostics remain within the project's operating requirements. Runtime update speed and CPU cycle time are separate measurements; one does not establish the other.
Version and scope limits
The ticket does not name PCS 7/WinCC versions, CPU model, tag type, trigger cycle or meaning of “ES variables.” The WinCC V8.1 performance note is not universal to all releases. Use the version-matched documentation and compare the actual project configuration.
Verification
Observe the AS signal and cycle-time diagnostics while checking the corresponding WinCC tag value and button color. If comparing ES-managed and direct DB tags, hold the displayed signal, update cycle and Runtime load constant. Record scan time, update delay, tag count and cycle settings; the source provides no measurements or evidence that either tag choice caused an increase.
Limitations and Operational Precautions
Changing tag acquisition cycles can increase requests and communication load. Do not select an unnecessarily fast cycle for static overview colors. The evidence does not support a blanket claim that WinCC objects have no relationship to system load, nor does it show that an ES tag is inherently more expensive than a DB tag.
Engineer FAQ
Does an ES tag inherently increase PLC scan time compared with a DB tag? The source and available evidence do not show an inherent difference. Check the actual program, tag acquisition and communication configuration.
What setting controls how quickly WinCC sees a changing tag? The relevant WinCC tag acquisition/trigger cycle, as configured for the version and tag usage.
Can a fast WinCC trigger affect performance? Yes. Siemens' V8.1 documentation warns that cyclic trigger cycle time affects project performance and advises sub-second cycles only when rapidly changing variables must be queried.
Will changing the tag source prove the cause of a cycle-time increase? No. Measure AS cycle time and Runtime update behavior while controlling other variables.
What should be checked for a button-color update? Confirm the mapped tag, its live value, the button's dynamic property and the tag's update cycle.
Technical References
- Siemens, SIMATIC HMI WinCC V8.1 – Working with WinCC (Part 1), §5.3 “Trigger Types,” discussing cyclic triggers, tag requests and performance impact. Official PDF access returned HTTP 403 during research: https://support.industry.siemens.com/cs/attachments/109986766/WinCC_Working_with_WinCC_Part1_en-US_en-US.pdf
- Siemens, SIMATIC PCS 7 Operator Station (V9.1), configuration manual for PCS 7 process-tag/OS engineering; official PDF access returned HTTP 403 and the ticket's release is unknown: https://support.industry.siemens.com/cs/attachments/109805404/ps7phosb_en-US.pdf