Resolving SINAMICS S120 Faults on SIMOTION D435 Crane Systems

System Overview: SINAMICS S120 and SIMOTION D435 on Goliath Cranes

The reported machine is a goliath crane commissioned in December 2012 and built around a SIMOTION D435 motion controller, two SIMOTION CX32-2 (or CX35-2) control extensions, and a distributed SINAMICS S120 drive line-up. The drive population covers two trolley cross-travel axes (lower and upper), four hoist axes (MH1, MH2, MH3, AH), and two long-travel axes for the legs (fixed and hinged). The D435 runs the SIMOTION runtime with PROFIBUS or PROFINET linking it to the SINAMICS Active Line Module (ALM) and the Smart Line Modules that feed each Smart Motor Module cluster.

After years of service, recurring alarms are now appearing on drives that are idle - that is, in the standby window 6-8 hours after the last motion command. The fact that a single cold power-cycle clears every alarm is the strongest single clue in the field report: it indicates that the underlying issue is not a permanent hardware defect, but a state that resets when 24 V control voltages and DRIVE-CLiQ nodes are re-initialised. The standard first-pass suspects for this pattern on a 12-year-old SINAMICS / SIMOTION system are 24 V supply quality, DRIVE-CLiQ / PROFIBUS / PROFINET communication quality, and EMC coupling on long cable runs through the crane structure.

Fault Inventory and Classification

The full set of alarms reported on the four affected axes is grouped below. Cross-reference the alarm number against the SINAMICS S120/S150 List Manual (6SL3097-4CA00-0RP0) and the SIMOTION D4xx Commissioning and Configuration Manual for the exact reaction class, acknowledgement behaviour, and cause-value bitfield. The List Manual is the only authoritative source for the cause-value breakdown of F3xxxx alarms; the SIMOTION SCOUT diagnostic buffer is the authoritative source for the F1xxx / F3xxx technology alarms.

Root-Cause Analysis: Why Faults Appear After 6-8 Hours of Standby

Three failure mechanisms dominate this symptom pattern on legacy SIMOTION / SINAMICS systems:

1. 24 V Control Voltage Sag and Brownout

The SINAMICS S120 Control Unit (CU320-2 DP / CU320-2 PN), the Active Line Module, each Smart Line Module, each Motor Module, and every SMC/SME sensor module is supplied from the 24 V control bus. If the 24 V rail sags below the published tolerance (typically 20.4 V to 28.8 V at the terminal, with 24 V nominal), internal DC-DC converters drop out, the DRIVE-CLiQ node stops sending sign-of-life telegrams, and the CU raises F31885 / F30008. On a goliath crane, the 24 V supply is normally fed from the panel-mounted SITOP PSU through long cable harnesses that run parallel to the S120 power busbars; voltage drop is significant on harnesses older than a decade.

Mechanism that biases faults to appear in standby: during motion, the SINAMIX / line contactors switch high current and the resulting sag masks the standby problem because the system is already in an unstable voltage regime. After the crane stops, mains transients from upstream equipment (cabin fans, lighting inverters, anti-collision radar) continue to load the 24 V rail. A weak SITOP or aged electrolytics on the 24 V distribution board will fail to ride through these transients, and the alarms arrive hours after the last motion because that is when the cooling fans, hoist brake release, and trolley inverters all power down at once and the 24 V supply is left supporting only the control electronics - which is exactly when a marginal PSU fails.

2. DRIVE-CLiQ Topology and EMC

DRIVE-CLiQ is a 100 Mbit/s serial link that is not electrically isolated from the chassis at the connector end and is sensitive to capacitive coupling from the S120 power cable looms. Standard SINAMICS practice is:

• Maximum 100 m per DRIVE-CLiQ segment using the official DRIVE-CLiQ signal cable 6SL3060-4Axx-0AA0 (drag-chain and trailing versions exist).
• Mandatory equipotential bonding between the S120 cabinet ground and the motor frame at the motor junction box, with the cable shield terminated 360 degrees at both ends.
• Separation of DRIVE-CLiQ cables from power cables by at least 200 mm, or use of a partitioned cable tray.

On a 12-year-old crane, common EMC degradation points are oxidised shield backshells, broken or missing bonding straps across hinged sections of the gantry, and DRIVE-CLiQ connectors that have been re-seated multiple times and lost their spring contact tension. All three produce intermittent F31885 / F30885 with cause values that point to sign-of-life counter overflow.

3. PROFINET / PROFIsafe Watchdog and Cycle Timing

F35851 and F35887 are PROFINET-layer alarms, not DRIVE-CLiQ. They appear when the PROFINET controller (the SIMOTION D435 with its CBE30-2 PN module) fails to exchange the configured number of update cycles within the watchdog window. The watchdog is set on the PROFINET device side; if it is left at the default of 3 missed updates, even a single late PROFINET frame from a switch that is rebooting after a 24 V dip is enough to passivate the safety slot and raise F35887 on every SINAMICS drive that holds a PROFIsafe slot.

Standby-bias mechanism: PROFINET switches on the trolley use store-and-forward buffering. A switch that loses 24 V drops out of the ring; the SIMOTION controller only sees the loss after the PROFINET watchdog expires. Time-alignment of multiple drives entering F35851 / F35887 within seconds of each other is a strong indicator of a 24 V disturbance, not a cable fault.

Diagnostic Procedure (Pre-Remediation)

1. Capture the diagnostic buffer before power-cycling. In SIMOTION SCOUT, open the affected axis, then go to Target System > Diagnostics > Diagnostic Buffer. For SINAMICS drives, open Starter / SCOUT online, select the drive, and read r0945, r0947, r0948, r0949, r2122-r2125. Export the buffer to a CSV and time-stamp the export. The exact cause value is what determines the next step.
2. Time-stamp the fault events. Enable the SINAMICS time stamp (drive parameter p3100 = 1) and the SIMOTION system clock. Plotting the time of each F3xxxx alarm against hoist brake release, cabin fan start, and 24 V events narrows the field to one or two subsystems.
3. Measure the 24 V rail at the SINAMICS terminals. Use a true-RMS datalogging meter (Fluke 289, Hioki PW3198, or similar) on the X1 terminal of the CU320-2, the X1 of each line module, and the X1 of each Motor Module. Log for at least 24 hours including one full shift and one full standby period. The acceptance window is 20.4 V to 28.8 V; excursions of more than 1 V below 24 V sustained for more than 10 ms are the smoking gun for the symptom pattern described.
4. DRIVE-CLiQ quality check. From SCOUT, navigate to Drive > Communication > DRIVE-CLiQ Diagnostics and read r9926, r9927 of each affected drive. Any drive reporting non-zero error counters in r9926 or r9927 must be re-cabled before parameter work.
5. PROFINET diagnostics. Open the PROFINET topology in SCOUT or TIA Portal (depending on commissioning tool version - SIMOTION D435 with firmware V4.4 and earlier is typically commissioned in SCOUT; V4.5 SP1 and later use TIA Portal). Read the port statistics of every PROFINET switch and the CBE30-2 module. Discarded frames, CRC errors, and late frames on the same port across multiple faults is the signature of a 24 V brownout on a single switch.

Step-by-Step Remediation

Step 1 - Stabilise the 24 V Supply

1. Replace any SITOP PSU older than 8 years with a current production unit. The Siemens SITOP modular and SITOP PSU8600 ranges are specified for crane environment; the modular line accepts redundancy modules for parallel operation, which is the recommended configuration for crane control supplies.
2. Add a 24 V buffer module (SITOP BUF1200 6EP4231-0AA00, or the PSU8600 buffer module 6EP4233-0AA00). The buffer module bridges short mains dips of up to several hundred milliseconds and is the single most effective countermeasure for the 6-8 hour standby pattern. The buffer module's bridging time should be sized to cover the longest of the observed sags plus a 100 ms safety margin.
3. Re-measure the 24 V rail at the SINAMICS terminals after the buffer module is in service. Confirm that the worst-case excursion over a 72-hour recording window stays inside the published tolerance.

Step 2 - Repair DRIVE-CLiQ Wiring and Bonding

1. Re-terminate every DRIVE-CLiQ connector in the affected drive cluster. Use the official DRIVE-CLiQ cable 6SL3060-4Axx-0AA0; the cable is rated for the SIMOTION / SINAMICS signal levels and is the only cable Siemens warrants for the link.
2. Inspect every bonding strap between trolley and bridge, between bridge and leg, and at the hinged leg pivot. Replace any strap with more than 0.1 ohm end-to-end resistance; the target is < 0.03 ohm for each bond.
3. Confirm 360-degree shield termination on every motor power cable at the motor junction box and at the SINAMICS Motor Module output. Pigtail terminations are the most common EMC defect on 10-year-old cranes and are a guaranteed source of intermittent encoder and DRIVE-CLiQ faults.

Step 3 - Tighten PROFINET Configuration

1. In the SIMOTION project, open the PROFINET configuration and increase the watchdog factor on the SINAMICS drives from the default 3 to a value of 6 or higher, but only if the safety function allows it. For PROFIsafe slots, the watchdog is part of the safety validation and must not be changed without re-validating the safety function.
2. Replace any unmanaged PROFINET switch with a managed switch that supports SNMP and LLDP; this gives a permanent record of port errors and allows remote diagnostics from the SIMOTION D435 commissioning port.
3. Set the CBE30-2 PN module's send clock to match the SINAMICS drive's PROFINET cycle, typically 1.0 ms for S120 with current firmware. A mismatch of one send clock is a known cause of F35851 on cranes that have been re-commissioned with mixed firmware.

Step 4 - Update Firmware and Configuration

1. Cross-check the firmware version of the CU320-2 on every drive against the SINAMICS S120 firmware release notes. The current SIMOTION D435 firmware line and the matching SINAMICS S120 firmware must be on the compatibility matrix published in the SIMOTION D4xx Commissioning Manual. Mixing V4.3 SIMOTION with V5.2 SP3 SINAMICS is one common source of F30885 / F30889.
2. If the SIMOTION D435 firmware is older than V4.4, plan an upgrade to the latest supported service pack. The upgrade brings the diagnostic buffer to the extended format and the CBE30-2 to a current PROFINET stack; both reduce the rate of F35851 / F35887 in standby.
3. After any firmware change, run a full download to the SIMOTION D435 and a RAM-to-ROM save on every SINAMICS drive. Power-cycle the entire system once and re-validate the safety function before returning the crane to service.

Verification

Run the crane through a full commissioning routine after every change. The routine below is the minimum acceptance test for the symptom pattern described.

1. Operate each axis through its full travel at low speed (10% of rated) and at rated speed. Record drive diagnostics buffers before and after.
2. Leave the crane in standby for 24 hours with all drives enabled (the standard standby condition on a goliath crane; do not switch off contactors for this test). Read the diagnostic buffer on every drive and the SIMOTION technology alarms; the count of new F3xxxx alarms should be zero.
3. Repeat the 24-hour standby for three consecutive cycles. Pass criterion: zero F30885, F30889, F31885, F30008, F35851, F35887, F30027 events on all four affected axes.
4. Capture a 72-hour 24 V datalogger record and confirm that the rail stays inside 20.4 V to 28.8 V at every SINAMICS terminal.
5. Validate PROFIsafe parameters (F-CPU signature, F-destination address, F-monitoring time) against the safety validation report; any change to the PROFINET watchdog must be reflected in the safety case.

Preventive Maintenance Schedule

Spare Parts Reference

Refer to the SINAMICS S120/S150 List Manual and the SIMOTION D4xx Commissioning Manual on the Siemens Industry Online Support portal for the definitive part numbers and the compatibility matrix between SIMOTION runtime and SINAMICS firmware. Field engineers should open a support request on the Siemens support portal and provide the diagnostic buffer export plus the 24 V datalogger recording; both accelerate the response considerably.

When to Escalate to Siemens Support

If the diagnostic buffer still shows F31885 with non-zero DRIVE-CLiQ error counters after the 24 V stabilisation, DRIVE-CLiQ re-termination, and PROFINET reconfiguration described above, escalate. The pattern at that point points to a failing Control Unit, a failing Smart Motor Module, or a firmware incompatibility that requires a controlled commissioning sequence with the SIMOTION hotline engineer on the line. Before escalating, prepare:

• The diagnostic buffer export from SCOUT (CSV) with timestamps.
• The 24 V datalogger recording (CSV) at the CU320-2 X1 of the affected drive.
• The PROFINET topology screenshot with port error counters.
• The SIMOTION D435 and CU320-2 firmware version report (read r0018 on every drive and the version displayed in SCOUT for the D435).
• A list of all parameter changes made during the diagnostic phase, with the previous and new values.

FAQ