Resolving SINAMICS S110 F07995 Pole Position Identification Fault on 1FK7 Motors

Fault Overview

The SINAMICS S110 single-axis servo drive raises fault F07995 "Drive: Pole position identification not successful" during the first commissioning, after a DRIVE-CLiQ topology change, or following an encoder substitution, when the rotor pole position identification (PolID) routine is unable to lock on the absolute rotor angle. The fault value stored in r0949[0] decodes the specific reason for the failure. Fault value 8 — the one encountered on a S110/PM340/1FK7 system — means: "The pole position identification routine current required is greater than the maximum current the power unit can deliver."

For 1FK7 servo motors equipped with multi-turn or single-turn absolute encoders connected over DRIVE-CLiQ, pole position identification is not normally required. The absolute rotor position is already resolved inside the encoder electronics at power-up and is transferred to the Control Unit through DRIVE-CLiQ. Running PolID in this case not only wastes time on the first start, it can also raise F07995 if the PolID parameters were automatically written from motor data, and the resulting current demand is above the converter's maximum capability (p0209).

System Hardware Used in the Field Case

Documentation references for these components:

• SINAMICS S110 product page — Siemens Support: SINAMICS S110
• SIMOTICS S-1FK7 catalog — Siemens Mall: 1FK7042-2AF71-1QA0
• PM340 Power Module (Blocksize) manual — SINAMICS S110 List Manual (function parameters, fault list)

The combination of a 0.8 kW motor with a 0.75 kW PM340 is a valid one. SINAMICS allows the motor rated current (p0305) to differ from the power unit rated current, provided it does not exceed the power unit's maximum current p0209. The drive will auto-configure the current limit and overload behavior from the motor and power unit data read through DRIVE-CLiQ.

Fault Code Reference: F07995 with r0949 = 8

The full fault string reported by the S110 firmware is:

F07995 Drive: Pole position identification not successful (8)
   Cause: The pole position identification routine current required is greater than the maximum current.
   Remedy:
     - Reduce the currents for the pole position identification routine (p0329, p0325, p1993).
     - The power unit cannot provide the necessary pole position identification routine current
       (p0209 < p0329, p0325, p1993). Replace the power unit with a power unit that has a higher
       maximum current.

Full list of F07995 fault values and their meaning, taken from the SINAMICS List Manual:

Root Cause Analysis

Parameter snapshot read at the time of the fault:

The current requested for pole position identification — particularly the value stored in p0329 and p1993 — exceeds p0209 = 3.4 A on the 0.75 kW PM340. The power unit cannot deliver that current even briefly, so the PolID algorithm aborts and the drive raises F07995 with r0949 = 8.

Two facts make this situation particularly easy to misdiagnose:

1. The motor is fully capable of running on this power unit. Rated current (~2 A) is well below the power unit's continuous limit. The fault is not a load-side sizing issue.
2. The PolID currents are populated automatically from the motor's electronic rating plate at first commissioning. The user cannot reduce them by manual parameter write, because the system rejects writes to p0329, p0325, and p1993 when the drive is online and the motor data set is in use. Manual scaling is also undesirable — it would distort the PolID measurement if PolID were actually needed.

Solution: Disable PolID with p1982 = 0

For a 1FK7 with absolute encoder option (DRIVE-CLiQ, multi-turn or single-turn), the absolute rotor position is already valid in the encoder. PolID does not need to run. Disable it at the parameter level:

Procedure

1. Open the drive in STARTER (or SINAMICS Startdrive in TIA Portal). Navigate to Configuration → Drive configuration → Pole position identification.
2. Set p1982 = 0 (Pole position identification not active). The drive will no longer request PolID at power-up.
3. Save the project to the drive (RAM → ROM) and power-cycle the Control Unit. A software-only reset is not sufficient because p1982 is read at the start of the next initialization.
4. Re-test motion: jog the motor from the STARTER control panel. The motor should run without F07995.

Acceptable values for p1982

Why p1982 = 0 Is Correct Here

The 1FK7042-2AF71-1QA0 is a 1FK7 with the DRIVE-CLiQ absolute encoder option (model code "7_1" or "1QA0" — singleturn/multiturn, 24-bit). At power-up the encoder transmits the absolute rotor position (cos/sin interpolator value) to the Control Unit via DRIVE-CLiQ, fully resolved. The closed-loop current controller is therefore able to inject the d-axis current at the correct electrical angle from the very first cycle. Pole position identification is not required for commutation and is not required for safe operation in this configuration.

Disabling PolID is the standard Siemens recommendation in this case. PolID is reserved for:

• Motors that do not transmit absolute position (resolvers, incremental encoders, third-party motors).
• Encoders whose absolute data has been corrupted or never recorded.
• Replacement motor scenarios where the encoder memory has been lost.

Verify the Motor Cable Wiring

Even after PolID is disabled, an incorrectly phased motor cable can produce rough running, oscillation, or F31110/F07995-like behavior. The drive-to-motor power connections must follow the standard Siemens phase mapping:

Drive (PM340 U2/V2/W2)  →  Motor (U/V/W)
   U2                       →   U
   V2                       →   V
   W2                       →   W

A field proven sanity check: swap any two of the three motor leads. The motor must not run in the opposite commanded direction. If it does, the original wiring was correct and another factor is at play. If it now runs in the correct direction after the swap, the leads were crossed at install.

For shielded power cables, ground the shield on both ends (360° bonding at the motor terminal box and at the drive gland plate) to keep common-mode currents off the encoder. Encoder cables must be DRIVE-CLiQ, ≤ 100 m between any two nodes, and routed at least 200 mm away from power cables.

Alternative: Sizing for a Larger Power Unit

If PolID must remain enabled (e.g., the application requires encoder replacement in the field or the absolute data is suspect), the only firmware-level fix is to install a power unit whose p0209 is greater than the largest PolID current in the parameter set. For the parameter values encountered (p0329 = 3.8 A, p1993 = 1.76 A, p0325 = 0.513 A), a PM340 with a peak current rating of at least 4.0 A would be sufficient.

Typical PM340 substitutions in the same 400 V 3 AC class:

Upgrading the power unit is more expensive and may force a re-rating of the line filter, line reactor, and braking resistor. For a 1FK7 with absolute encoder, p1982 = 0 is the recommended path; the power unit replacement is only justified when PolID is functionally required.

Parameter Reference

Verification Procedure

1. Confirm r0947[0] no longer reports F07995. The fault buffer holds the previous entry until cleared, so issue a fault acknowledgement (OFF1 then ON), or use acknowledge from STARTER, then read the buffer again.
2. Verify p1982 = 0 in the expert list. STARTER will show the value 0 in bold when it has been written to ROM.
3. From the STARTER control panel, jog the motor at 100 rpm for 5 seconds in each direction. Listen and feel for smooth rotation. Rough running or cogging indicates a phase-mapping error — swap motor leads and re-test.
4. Enable a small load step on the motor (e.g., lightly pinch the shaft) and verify the current controller responds without overshoot. Use the STARTER trace to record r0079 (torque setpoint) and r0031 (actual current) — they should follow within < 5 ms.
5. Run a full motion profile matching the real machine cycle. Capture r0947 and r0949 throughout. F07995 should not reappear.
6. Save the project to the S110 and back up the parameter set on the engineering PC.

Common Pitfalls

• Writing p1982 online and not saving to ROM. A power-cycle reverts the drive to the previous state, and the fault reappears on the next startup. Always write to ROM and cycle power.
• Modifying p1982 on the wrong drive object. The S110 has only one drive object, so this is rarely an issue, but on multi-axis S120 systems the PolID setting lives on the servo object — not on the CU or the infeed.
• Setting p1982 = 0 on a motor that does need PolID. The motor will run, but at the first start the drive will inject current at an arbitrary angle. If the motor has a non-zero load at standstill it may jerk, and on a vertical axis the load may drop. Verify the encoder type and absolute-track status before disabling PolID.
• Believing the drive's rating-plate limits. p0209 is set by the power unit firmware; it cannot be raised in software. The hardware limit is the only valid limit.

Related Faults

FAQ