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PROFIsafe F-monitoring time (F_WD_Time)

A PROFIsafe connection goes to a safe state when the next valid safety message does not arrive within F_WD_Time, a monitoring time in milliseconds that you set for each F-device.

Ben RutterIndustrial network engineer
Vendor or body
PROFIBUS and PROFINET International (protocol); values as documented by Siemens
Model or version
PROFIsafe over PROFINET; Siemens SIMATIC Safety in TIA Portal
Last verified
Oct 5, 2026
Sourced values
9

Values

ParameterValueCondition
F_WD_TimeWatchdog in ms1An F-Parameter the F-Device receives at startup. It sets a watchdog timer, in milliseconds, that monitors the reception of the next valid PROFIsafe message (SPDU).
Reaction when communication failsSafe state1PROFIsafe communication errors switch the F-Host driver into a safe state. A return to normal operation is usually not allowed without operator acknowledgment.
Where it is set (Siemens)CPU, interface, or F-I/O2Siemens calls F_WD_Time the F-monitoring time. You set a default for central F-I/O in the F-CPU properties, a default per PROFINET or PROFIBUS interface, or an individual value in each F-I/O. Changing it changes the safety program, so a new acceptance may be required.
Default for GSD based F-devicesFrom the GSD file2For fail-safe GSD based I/O devices, the F-monitoring time in the device GSD file becomes the default when the device is plugged in. You can change it.
F-monitoring time range1 to 65535 ms3Example module ET 200MP F-DI 16x24VDC (6ES7526-1BH00-0AB0). Ranges are module specific.
Default F-monitoring time, S7-1500HF systems2300 ms2Default for F-I/O in a redundant HF system, sized for an MRP ring. Siemens says a line topology can use a value smaller by a factor of about 2.
Minimum F-monitoring timeCalculated per system2Siemens: the PROFIsafe monitoring time must be long enough that it does not trip when no fault is present. Siemens provides an Excel file (entry 109783831) to calculate the minimum.
Role in safety function response timeAdds a delta1PI: the safety function response time is the total worst case delay time plus, for one failed part, the difference between its watchdog time and its worst case delay time.
Wireless transmissionPermitted1PI permits wireless transmission as long as sufficient availability (no nuisance trips) and security can be guaranteed. For IEEE 802.11, only infrastructure mode is permitted, not ad hoc mode.

Sources

  1. PROFIsafe System Description, Technology and Application (Order No. 4.342). Read Oct 5, 2026.
  2. SIMATIC Safety, Configuring and Programming, Programming and Operating Manual (A5E02714440-AR). Read Oct 5, 2026.
  3. Digital input module F-DI 16x24VDC (6ES7526-1BH00-0AB0) Manual (A5E03858068-AA). Read Oct 5, 2026.

About this page

Built from 3 sources: 1 protocol owner or alliance and 2 vendor documents. Researched and drafted with AI assistance, then reviewed and approved by Ben Rutter on . How pages are made

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Cite this page

Plain

Ben Rutter. "PROFIsafe F-monitoring time (F_WD_Time)." OT Wireless, published October 5, 2026. https://otwireless.com/requirements/profisafe/

APA 7

Rutter, B. (2026, October 5). PROFIsafe F-monitoring time (F_WD_Time). OT Wireless. https://otwireless.com/requirements/profisafe/

BibTeX

@misc{rutter2026profisafe,
  author = {Rutter, Ben},
  title = {{PROFIsafe F-monitoring time (F\_WD\_Time)}},
  year = {2026},
  howpublished = {\url{https://otwireless.com/requirements/profisafe/}},
  organization = {OT Wireless},
}