Resolving SINAMICS F07490 in EPOS with PROFIsafe SS1E Functions

F07490 is one of the most persistent and misunderstood faults reported by SINAMICS S120, SINAMICS S210, and compatible SINAMICS drive platforms when the basic positioner (EPOS) is paired with PROFIsafe Extended Safety Functions. The alarm appears the moment an axis is stopped by a safety event such as SS1, an emergency stop that maps to OFF3, or a Safely Limited Speed violation that drops the drive enable. Once F07490 is raised, the operator must acknowledge it through STARTER, TIA Portal, or a PLC reset bit before the cycle can resume. In continuous-process machinery this behavior is unacceptable because it forces manual intervention on every safe stop.

The fault is not caused by a misconfigured EPOS block or a bad mechanical parameter. It is caused by the priority structure inside the SINAMICS firmware: PROFIsafe safety functions outrank EPOS and remove the drive enable signals before the positioner can halt the traversing task gracefully. The engineering fix is to use SS1E (Safe Stop 1 Extended), a safety function specifically designed to hand control of the deceleration phase back to the application controller before torque removal is applied.

Overview of SINAMICS F07490 in EPOS Positioning Mode

F07490 belongs to the F07xxx fault group on SINAMICS drives. This group is reserved for positioning-mode (EPOS) errors. F07490 is generated when the drive detects a missing enable condition while a positioning operation is active. The most common triggering conditions are:

• OFF1, OFF2, or OFF3 is revoked while a traversing block, MDI block, or jog command is executing.
• The EPOS setpoint enable (r898.8 in many firmware versions, or r2090.8 in others) is cleared mid-traverse.
• A safety function that drives OFF3 internally (SS1, SS2 with default configuration, or a hard-wired emergency stop mapped to OFF3) interrupts the axis.

When F07490 is raised, the drive enters fault state, the pulses are not necessarily cleared immediately, and the fault must be acknowledged by setting the acknowledge edge on bit 7 of STW1 (control word 1) through PROFIdrive, or via STARTER's commissioning interface.

Root Cause: PROFIsafe Safety Priority Over EPOS

The SINAMICS firmware implements a strict, hard-coded priority chain for control signals. From highest to lowest priority, the order is:

1. Safety Integrated functions (STO, SS1, SS1E, SS2, SOS, SLS, SDI, SLP).
2. Hardware inputs (terminals for safe inputs, F-DI).
3. Drive enable logic (r898 enable bits).
4. EPOS setpoint channel (r2090 EPOS STW).
5. Standard PROFIdrive setpoints (r2050 control words, n-set).

When a safety event such as SS1 is requested via the PROFIsafe telegram, the following sequence occurs by default:

1. The safety logic in the SINAMICS Control Unit (CU320-2 or CU310-2) accepts the SS1 selection from the PROFIsafe host (F-CPU).
2. The drive firmware initiates an internal OFF3 ramp using the configured OFF3 ramp-down time (p1135).
3. OFF3 removal drops OFF1, OFF2, and OFF3 in the drive's internal control word, which propagates to the EPOS task as a loss of enable.
4. The EPOS task, which is mid-traverse, sees the enable removal and raises F07490 because the positioner cannot finish its commanded motion under these conditions.
5. After p1135 expires, STO is engaged and torque is removed. The drive is now safe but faulted.
6. The operator must clear F07490, reset the safety acknowledgment, and re-trigger the cycle.

This priority arrangement is correct from a safety perspective - the drive must be capable of stopping the axis even if the PLC has failed. However, it forces a behavior conflict when EPOS is the active motion task. The application needs to bring the axis to a controlled halt using EPOS commands, but the safety function removes control before that can happen.

PROFIsafe Extended Safety Functions Overview

The Safety Integrated Extended Functions available on SINAMICS drives cover a wide spectrum of stop and monitoring behaviors. Selecting the right function is the foundation of any EPOS-safety integration:

Only safety functions that do not drop OFF1/OFF2/OFF3 during the controlled stop phase are compatible with EPOS without generating F07490. SS1E is the canonical solution for stop-on-safety events. SOS, SLS, SDI, and SLP are appropriate when the safety goal is monitoring rather than stopping.

The SS1E Solution: Safe Stop 1 Extended

SS1E reverses the priority model used by SS1. With SS1E, the drive firmware does not trigger any ramp internally. Instead, the firmware starts a configurable timer (p9556, SS1E delay time) and signals the application that SS1E has been selected. The application has the full duration of the timer to bring the axis to a halt using EPOS commands. Once the timer expires, the drive engages STO and removes torque.

The full SS1E sequence is:

1. The F-CPU writes the SS1E selection bit into the PROFIsafe control word. In telegram 30, this is bit 2 of the safety control word 1 (S_STW1). In telegram 31, the bit position depends on the configured safety slot mapping (typically p10030[0] for S_STW1).
2. The SINAMICS safety firmware receives the SS1E request and starts the safe timer p9556.
3. The drive enable signals (r898 bits) remain active. EPOS sees no change in enable state.
4. The application logic detects the SS1E selection, typically by reading the safety status word back (S_ZSW1 bit 4 in telegram 30 indicates safe stop active). The application issues an EPOS halt: STW1.4 (jog/positioning enable) cleared, or EPOS velocity override written to zero.
5. EPOS ramps the axis down using its configured deceleration limit (p2573) and brings the axis to a standstill within the EPOS positioning window.
6. When p9556 expires, the drive firmware engages STO. The safety status word indicates STO active. Torque is removed.
7. No F07490 is generated because OFF1, OFF2, and OFF3 were never revoked during the EPOS traversal.
8. When the safety event is cleared (operator reset), the F-CPU removes the SS1E selection and re-enables the axis. EPOS can resume without fault acknowledgment.

Prerequisites and System Requirements

Implementing SS1E with EPOS requires the following:

The PROFIsafe telegram 30 layout is structured as two 16-bit words for safety control and status. Telegram 31 extends to four words and includes safe encoder feedback. For SS1E-only applications, telegram 30 is sufficient and reduces PROFIsafe cycle time.

Configuring SS1E in STARTER: Step-by-Step Procedure

1. Open the SINAMICS drive object in STARTER and connect online.
2. Navigate to Functions → Safety Integrated → Extended Functions.
3. Set the safety configuration mode by selecting the password and entering the safety commissioning mode (drive must be in standby, no pulses enabled).
4. In the safety function selection matrix, enable SS1E instead of SS1. SS1 should remain disabled or configured as a fallback only.
5. Configure the SS1E delay time at p9556. Set the value in seconds; typical range is 0.5 to 3.0 s for EPOS axes.
6. Configure the PROFIsafe telegram slot assignment. Under Communication → PROFIsafe, select telegram 30 or 31.
7. Map the safety control word source. For telegram 30, the standard assignment is S_STW1 mapped to PZD slot 5 (after the 4-word standard telegram). Confirm the slot offset in p2042 / p2071 if you are using a custom PZD layout.
8. Configure STW1 bit 0 (ON/OFF1), bit 1 (OFF2), bit 2 (OFF3) on the PLC side so that OFF1 is held high during SS1E. This is the most common mistake: do not drive OFF1 low during SS1E; leave it set so the drive remains enabled until STO is engaged by the SS1E timer.
9. Configure the EPOS response to SS1E selection. In the PLC application, when S_ZSW1 reports SS1E active, set EPOS STW1.4 = 0 (jog enable off) and write a velocity override of zero.
10. Save the safety parameters to the CF card and back up the project. Perform a safety acceptance test before production release.

Telegram Configuration and Bit Mapping

For a typical SINAMICS S120 EPOS axis with PROFIsafe, the PROFINET/PROFIBUS telegram structure is:

The PROFIsafe S_STW1 bit assignments for telegram 30 are:

Only one of bits 0-6 should be active at a time. Selecting STO and SS1E simultaneously is undefined behavior and may cause the drive to default to STO immediately.

EPOS Stopping Sequence and Timing Diagram

The SS1E sequence produces a deterministic timing profile that keeps EPOS in control throughout the controlled stop phase:

The diagram illustrates that between t1 (SS1E selection) and t3 (STO engagement), the drive enable signals remain active and EPOS is allowed to decelerate the axis using its own ramp. The PROFIsafe priority does not override OFF1/OFF2/OFF3 during this window.

Parameter Reference for SS1E and EPOS Integration

Troubleshooting Matrix for F07490

Verification and Acceptance Testing

After commissioning SS1E with EPOS, perform the following acceptance test sequence:

1. Configure the SINAMICS safety configuration mode and save to ROM (CF card).
2. Run the axis in jog mode at maximum permitted velocity. Trigger SS1E from the F-CPU. Verify: F07490 is not raised; the axis decelerates to standstill within p9556; STO engages at t = t1 + p9556; ZSW1.7 (axis stationary) goes high before STO.
3. Reset SS1E selection from the F-CPU. Verify: STO clears; drive returns to enabled state; EPOS can immediately accept new commands without fault acknowledgment.
4. Run the axis in MDI mode with a traversing block of 10 revolutions at maximum velocity. Trigger SS1E mid-traverse. Verify: F07490 is not raised; the axis decelerates; STO engages; the MDI block is reported as interrupted (ZSW2.10 = MDI active clears).
5. Run the axis in traversing block mode (multiple blocks queued). Trigger SS1E during block 5 of 10. Verify: F07490 not raised; block 5 is interrupted; after SS1E reset, the PLC can either resume from block 5 or restart from block 1.
6. Document the test results in the acceptance protocol. Sign and archive as required by IEC 61800-5-2 / EN ISO 13849-1 / IEC 61508.

Reference for the SS1E application description and EPOS integration: Siemens Support Entry 82526134 - EPOS with Safety Integrated Extended Functions.

Common Implementation Pitfalls

Several recurring configuration errors cause F07490 even when SS1E is selected. Watch for these during commissioning:

• OFF1 cleared during SS1E. The PLC must keep STW1.0 set while SS1E is active. Some safety libraries default to clearing OFF1 as part of the safe stop; this must be overridden for SS1E.
• Drive enable not released before SS1E selection. If the drive enable (r898.0) is not active when SS1E is selected, the SS1E timer has no effect on a non-enabled drive. Confirm that STW1.0 and the pulse enable chain are correctly established before the first SS1E test.
• p9556 shorter than the EPOS ramp time. EPOS uses p2573 maximum deceleration. For a 3000 RPM axis with p2573 = 5 rev/s², the deceleration time is 3000/60/5 = 10 s. p9556 must be larger than 10 s plus margin. Under-sizing p9556 causes F07490 because EPOS has not finished its ramp when STO engages.
• Jog enable not cleared by the PLC. When SS1E is selected, the PLC must clear EPOS STW1 bit 4 (jog enable). If the PLC leaves jog active, the drive receives contradictory commands (STO imminent but jog active) and may generate F07490.
• PROFIsafe substitution value misconfigured. If the PROFIsafe connection fails (F-CPU stop, wire break), the drive uses the substitution value. Default substitution for safety bits is 0, which selects STO directly. If the F-CPU is expected to drop offline frequently, configure the substitution value to select SS1E with a long timer rather than STO.

Alternative Architectures

If SS1E is not available on the drive firmware, or if the application requires a different stop category, several alternative architectures can be considered:

For most EPOS applications, SS1E is the canonical solution and is supported across the SINAMICS S120, S210, and G120 product lines. Where SS1E is not supported (legacy S110 firmware, certain G120 firmware variants), the SOS-based architecture is the cleanest alternative.

Related Faults and Their Meaning

F07490 is part of a family of EPOS-related faults. Understanding the surrounding faults helps disambiguate the exact triggering condition:

F07490 in a safety-interrupted EPOS application will be accompanied by F01018 or F01611 in the alarm history because the safety function that triggered it is logged separately. Inspecting r0947 (fault buffer) and r0949 (fault time) helps correlate F07490 with the safety event that caused it.

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