Resolving SINAMICS S120 F361 Sign of Life and DC Link

1. Problem Overview

A SINAMICS S120 booksize drive line-up controlled by a SIMOTION D425-2 (6AU1425-2AA00-0AA0) is exhibiting two distinct but related symptoms:

1. Faults F360:241D, F360:241E, F360:241F, and F360:2420 (Sign-of-Life failure, drive objects 3, 4, 5, 6) appearing in the SINAMICS Integrated diagnostics buffer.
2. DC link undervoltage faults when axis velocity exceeds approximately 35 % of setpoint. Below 35 % the axes run cleanly; above this threshold, the drive objects report a DC link collapse even though the Smart Line Module (SLM) line voltage and measured DC link voltage remain stable and the motor modules draw less than 1 A.

These two symptoms share a single underlying root cause: the Smart Line Module has not been activated through its proper sequence control. The drive is operating in an uncontrolled or partially-controlled state where the SLM precharging/bypass contactor logic has not been latched, so the DC link is held only by the precharge path. The first time the drive demands regenerative or motoring energy above the precharge capability, the controller samples the DC link as undervoltage and the SIMOTION/SINAMICS life-signing protocol is interrupted because the SLM is not in Run.

2. Affected Topology and Catalog Numbers

All catalog numbers map to the SINAMICS S120 booksize product line. The SLM is a 5 kW/10 kW/16 kW/36 kW family member with a 600 V DC link rated voltage. The motor modules are 2-axis variants that draw from a common DC bus. Refer to the SINAMICS S120 Booksize Power Units Manual for dimensional, fuse, and braking-resistor data.

3. Fault Code Analysis

All four F360 faults are reported in the same 20 ms window (16:11:14.654–691), confirming a single event. The structure of an F360 fault is documented in the SINAMICS S120/S150 List Manual as a "Life sign failure, drive object".

The 0x7533 component identifies the source as a CU/SIMOTION-to-DO cyclic communication timeout. The fault number 30003 is the PROFIdrive-mapped alias. The DC link undervoltage fault that follows is a secondary consequence: when the SLM is not in operation, drive-side monitoring interprets the floating or precharge-only DC link as a fault condition.

4. Root Cause: Smart Line Module Not Activated

The Smart Line Module in booksize format requires two contactors to be sequenced by the SLM internal state machine:

1. Precharging contactor — connects the line through precharge resistors to limit inrush.
2. Bypass (main) contactor / circuit breaker — short-circuits the precharge path once DC link is charged.

Both are wired through the SLM's X9 terminal block. If X9 is unwired, the SLM reports ready in online mode for the configuration view but is physically unable to close its contactors. In this state, r0863.0 (infeed operation) toggles, and the controller cannot consistently life-sign with the downstream drive objects.

4.1 X9 Connector Pinout (6SL3130-6TE21-6AA4)

The SLM closes the precharging contactor, waits for the DC link to reach the threshold (typically 80 % of rectified peak), then closes the bypass. If a circuit breaker is used instead of a contactor, it must be equipped with an instantaneous undervoltage (UVR) release — a thermal/magnetic breaker is not acceptable because the brief overlap between precharge-open and bypass-close would let the breaker open on inrush.

5. SLM Configuration and Parameter p922

On a DRIVE-CLiQ-attached infeed, the SLM is auto-discovered and the ready signal r0863.0 is interconnected to the drives' p0864 (infeed operation) by the topology wizard. However, the SIMOTION program must still command the SLM on. Two control paths exist:

• Implicit (BICO) — set p922 = 999 (free telegram configuration via BICO). The SIMOTION MCC chart or the function block _lineModule_control manipulates the control word directly via BICO source.
• Explicit (Telegram 370) — set p922 = 370. The SIMOTION sends the SLM control word (STW) and reads the status word (ZSW) cyclically via PROFIdrive telegram 370.

If p922 is left at 999 and the SIMOTION subsequently re-uses the same logical I/O area for another slave, the SLM will be controlled by stray BICO bits. Always explicitly set p922 = 370 and ensure the HMI address list does not overlap.

5.1 Procedure: Switching p922 from 999 to 370

1. Open STARTER or Startdrive and go online with the SLM (DO 2).
2. Set p10 = 1 (quick commissioning filter).
3. Set p922 = 370.
4. Copy RAM to ROM.
5. Power cycle the SLM (24 V OFF/ON at X124).
6. Re-go online and confirm p922 = 370 persists after "Save project and compile changes" in SIMOTION Scout.

6. Telegram 370 Control Word and Status Word

PROFIdrive telegram 370 is the standard profile for the SINAMICS infeed. The control word (STW1 infeed, 16-bit) and status word (ZSW1 infeed, 16-bit) are mapped to the SIMOTION I/O variables LineModule_STW and LineModule_ZSW.

6.1 Manual Hand-Test Values

For bench verification without the SIMOTION program running, write the following control words directly to the I/O address:

• Switch OFF: 0x047E (binary 0000 0100 0111 1110) — bits 0 and 1 cleared, Off2 low-impedance path, no enable.
• Switch ON: 0x047F (binary 0000 0100 0111 1111) — bit 0 set, no OFF2, no OFF3, enable operation, enable setpoint.

7. SIMOTION Function Block _lineModule_control

The system function block _lineModule_control (declared in the SIMOTION system library, accessible from the Getting Started documentation) is the supported method for commanding the SLM. It manages the OFF1 edge, OFF2/OFF3 latches, fault acknowledgement, and the sign-of-life counter. The FB expects an axis reference or DO reference plus the STW/ZSW addresses.

Manual implementation requires the following state machine in the MCC chart:

1. Write 0x047E to LineModule_STW on cold start.
2. Wait for ZSW1 bit 0 (Ready to switch on).
3. Edge-trigger 0x047F (only on rising edge of bit 0).
4. Monitor ZSW1 bit 2 (Operation enabled) — set means SLM is in Run, drives will accept enables.
5. On ZSW1 bit 3 (Fault present), clear faults via bit 7 toggle and re-enter the OFF1 sequence.

Full FB documentation is in the SIMOTION D4x5-2 System Functions and FB Reference and the SIMOTION Getting Started — Commissioning Drive-Based Axes manual.

8. HMI / Mobile Panel Communication Conflict

A second-tier symptom appears when the SIMOTION address list is modified: the Mobile Panel 277 (PROFIBUS address 1) drops out, and X122 I/O availability shows "not synchronous". The root cause is bus cycle time. Adding LineModule_STW/LineModule_ZSW changes the PROFIdrive telegram list and triggers a Scout re-compile, which alters the bus configuration. The Mobile Panel must be re-downloaded with the new GSD/DPV1 configuration.

8.1 Resolution Steps

1. After any address-list change in Scout, recompile and download the HW Config to the SIMOTION.
2. Recompile the HMI project in WinCC flexible / TIA Portal.
3. Transfer the HMI project to the Mobile Panel (PN or USB).
4. Cycle PROFIBUS: power down the panel, then the SIMOTION, then re-power in order — panel first, then controller.
5. Verify X122 I/O status returns to "synchronous" in Scout diagnostics.

9. Step-by-Step Recovery Procedure

1. Power down the entire drive line-up. Verify zero voltage at the line side of the SLM with a CAT IV meter.
2. Inspect X9 wiring. Pins 3, 4, 5, 6 must connect to a contactor (or UVR-equipped breaker) coil. Confirm L1, L2, N supply for the coil is from a stable 24 V DC or 230 V AC source as specified by the contactor vendor.
3. Verify phase sequence at the precharge contactor input matches the main contactor input. Use a phase-sequence tester or a two-channel oscilloscope on L1-L2.
4. Confirm the EP (Enable Pulses) terminal at X9.1/X9.2 is jumpered to +24 V. Without EP, the SLM will not start its state machine.
5. Set p922 = 370 in STARTER/Startdrive, copy RAM to ROM, power-cycle the SLM.
6. Configure the SIMOTION MCC chart to call _lineModule_control (or implement the manual STW state machine in Section 7).
7. Compile and download the Scout project. Re-download the HMI project to the Mobile Panel.
8. Test with the axis control panel in Scout at 100 % setpoint on each axis individually. Confirm the SLM closes both contactors audibly and that r0863.0 = 1 throughout motion.
9. Run the production motion profile. Verify the diagnostics buffer is free of F360 and F30003 entries.

10. Verification Checklist

11. Preventive Measures

• Document the X9 wiring schematic in the EPLAN project and require a controlled drawing revision for any contactor change.
• Add a STARTER script to verify p922 = 370 at every cold start; alarm if it is 999.
• Use a thermal-magnetic circuit breaker with a UVR release sized for the SLM inrush. Do not substitute a standard breaker.
• Whenever HMI tags are added or removed, perform a coordinated Scout + HMI compile and download — never one without the other.
• Capture a STARTER trace of r0070, r0863.0, and r2065[0] during every commissioning sign-off and archive with the project.

12. Extended Diagnostic Parameters

FAQ