How Minimum and Maximum SFC Step Run Times Work
In SFC for SIMATIC S7 V9.0, Minimum defines a step's minimum active dwell, while Maximum is a timeout-monitoring limit when Time Monitoring is enabled. Maximum does not supply a clock-time start or establish automatic progression. If a process requires a dwell or timeout response, configure and verify those requirements explicitly rather than assuming that leaving the run-time fields unspecified preserves the intended timing.
Table of Contents
- Minimum Time and Maximum Monitoring
- Inspect and Configure the Step
- What Happens When No Time Is Configured
- Execution Timing and Step Errors
- Verification
- Limitations and Operational Precautions
- Engineer FAQ
- Technical References
- Related Articles
- Related Tags
Minimum Time and Maximum Monitoring
For SFC for SIMATIC S7 V9.0, Minimum sets a dwell time before normal transition-driven progression. Maximum supplies the monitoring threshold; it is not an instruction to advance to the next step.
The original question does not identify its installed SFC version. This explanation is scoped to the opened V9.0 manual rather than every release.
Inspect and Configure the Step
The manufacturer procedure is to double-click the step, or select it and choose Edit > Object Properties. On General, inspect the run-time values. Separately inspect the SFC operating parameters and the active step-control mode.
As engineering preparation, define two distinct process requirements before entering times: how long the action must persist, and how long it is acceptable to wait for completion. A minimum dwell does not demonstrate process completion; the transition should represent the required process condition.
What Happens When No Time Is Configured
The V9.0 test display uses dashes for run-time values configured as zero. A step without a configured minimum is not thereby proven to have zero execution time: the manual separately describes step-action processing and transition behavior.
If the process requires a dwell, specify and verify it deliberately. If the process needs timeout detection, check both the maximum and Time Monitoring state. Do not interpret an omitted run-time entry as a scheduled clock-time start; step activation is a separate sequence event.
Execution Timing and Step Errors
The manual bases run times on CPU time, not an OB-cycle count. Do not turn a duration setting into a guarantee of exactly two chart executions or use the manual's 1.5-second illustration as a universal tuning rule.
With monitoring enabled, exceeding the maximum reports a step error. Acknowledging it does not complete the step. The V9.0 manual also describes exceptions to minimum-time behavior for particular operator step modes and when command output is disabled; account for the actual operating mode during verification.
Verification
In an isolated test configuration, record step activation, transition satisfaction, progression and any timeout indication. Use the same SFC version and execution context as the intended application.
Prepare separate cases for an early-satisfied transition, a transition that remains false and the intended operator-control behavior. Compare observations with the process requirements before changing production timings. These are proposed acceptance cases, not claimed measurements.
Limitations and Operational Precautions
SFC run-time monitoring is not established here as a safety timing function or an automatic process recovery. Define the required response to a timeout separately.
Preserve the sequence baseline and assess the effect of a changed dwell or timeout on equipment and downstream steps. Perform live timing changes only under the plant's approved change procedure. Confirm the installed-version behavior before transferring the V9.0 explanation to another release.
Engineer FAQ
Does Maximum move the sequence on automatically?
No such behavior is established by the maximum-time monitor; it reports a step error when enabled and exceeded.
Does acknowledging the timeout complete the step?
The V9.0 manual explicitly says it does not.
Is Minimum a process-completion condition?
No. It supplies dwell-time behavior, while the required process condition belongs in the sequence logic.
Technical References
- Siemens: SFC for SIMATIC S7 V9.0, May 2017, A5E41356228-AA — section 12.4.2.1, step properties; sections 16.2.3–16.2.4, step modes and monitoring; section 16.3.6.2, step processing; section 17.5, runtime test display.