Problem Overview
A 1FK7103-5AF71 SIMOTICS servomotor reports drive-side winding temperatures of 98 °C while the same machine at the same load reads only 84 °C on an external pyrometer. Drive-reported torque (K241) is 40 % (≈5.6 Nm) and current (K242) is 30 % (≈3.6 A fundamental RMS) on a motor whose nameplate defines 14 Nm rated torque and 12 A rated current. The motor and the SBM (Sensor Box Module) have already been replaced, the three-phase clamp readings are symmetric, mechanical side (gearbox, coupling, process) has been validated, and the current trace looks stable. To keep the axis running, compressed air is forced across the motor housing. This pattern — overtemperature at apparently low utilization — is characteristic of one or more of: corrupted temperature-sensor signal, additional loss components not represented in the basic current display, encoder feedback degradation producing current-loop ripple, mechanical re-binding after the motor swap, or power-cable heat soak.
Identifying the Motor and Drive System
The 1FK7103-5AF71 is part of the SIMOTICS S-1FK7 family of naturally-cooled permanent-magnet synchronous servomotors with integrated absolute encoder via DRIVE-CLiQ. The type designation decodes as:
| Block | Value | Meaning |
|---|---|---|
| 1FK7 | — | SIMOTICS S-1FK7 series, brushless, naturally-cooled |
| 1 | 1 | Shaft height 1 (100 mm flange, BC flange-flange motor) |
| 03 | 3 | Core length code (matches length block; verify against nameplate) |
| 5 | 5 | Cooling method: naturally cooled (no fan) |
| AF | — | Winding code AF → specific torque/speed characteristic |
| 71 | — | Encoder option 71 = 22-bit singleturn + 12-bit multiturn absolute encoder via DRIVE-CLiQ (typically AS24DQI resolver emulation not used; built-in absolute) |
Verify the following nameplate values from the new motor sticker:
| Parameter | Nameplate Value | Engineering Note |
|---|---|---|
| Rated torque Mn | 14 Nm | Matches p354 = 14 set in the drive configuration |
| Rated current In | ≈ 12 A RMS | Continuous phase current at Mn and rated speed |
| Stall current I0 | ≈ 13.3 A RMS | Continuous standstill current |
| Rated speed nN | 2000 / 3000 rpm | Depends on AF winding variant |
| Max mechanical speed nmax | 5000 / 6000 rpm | Limited by bearings and field weakening |
| Insulation class | F (155 °C winding) | ΔT 80 K over 40 °C ambient max for continuous operation |
| Temperature sensor | KTY84-130 (typical) or PTC | Embedded in stator end-turn; leads exit on signal pins |
Motor Temperature Monitoring Architecture
The SINAMICS S120/SIMOTION system provides two parallel temperature inputs per axis:
- Motor thermal model (I²t) — driven by p0611 (motor thermal model time constant), p0612 (configuration), p0613 (motor overtemperature warning 12t threshold), p0614 (motor overtemperature alarm 12t threshold).
- Physical sensor — read through the SBM/SMC/SME Sensor Module that connects to the motor's KTY84 or PTC thermistor via the power/signal cable.
The 1FK7 motor feeds the temperature signal through two wires brought out of the power/signal connector at pins dedicated to the sensor pair (refer to the Siemens Motion Connect 500/800 signal-pinout map). The SBM transmits the value over DRIVE-CLiQ to the Control Unit and SINAMICS reads it as r0035[0] (motor temperature actual).
Critical parameters for the temperature channel:
| Parameter | Function | Typical Value |
|---|---|---|
| p0601 | Motor temperature sensor type | 0 = no sensor, 1 = KTY84, 2 = PTC, 4 = PT1000 |
| p0604 | Motor overtemperature threshold (warning) | 120 °C |
| p0605 | Motor overtemperature fault threshold | 130 °C (class F) |
| p0607 | Sensor monitoring time | 2.0 s typical |
| p0611 | Motor I²t thermal model time constant | 300–600 s for 1FK7103 |
If the sensor wires are open, shorted, or partially shorted to a phase conductor, the SINAMICS may either:
- Trigger F07012 (“Drive: motor overtemperature, sensor”) and shut the axis down, OR
- Read a biased temperature (e.g. −40 °C, a shorted value, or a stuck value) which fools the I²t thermal model into permitting excessive continuous current, eventually tripping F07011 (“motor overtemperature, thermal model”).
HMI Tag Mapping (K241 / K242) to SINAMICS Parameters
The tag list shows K241 mapped to “torque” and K242 to “current”. In a SINAMICS S120 / SIMOTION environment the typical references are:
| HMI Tag | SINAMICS Parameter | Unit | Description |
|---|---|---|---|
| K241 | r0027[0] (actual torque, smoothed) or r0079 (torque utilization) | Nm or % | Actual torque / rated |
| K242 | r0029[0] (output current, smoothed) or r0030 (current utilization) | A RMS or % | Phase current / drive rated |
Root-Cause Matrix
| Cause | Likelihood | Diagnostic Evidence | Remediation |
|---|---|---|---|
| Sensor signal degraded / intermittent / partially shorted | High | r0035 vs. pyrometer mismatch > 30 K; r0192 sensor-state bits; SBM LED pattern | Replace signal pair in hybrid cable; replace SBM |
| Insulation degradation → leakage current → I²R heating | Medium | Megger 500 V phase-to-ground; resistance < 1 MΩ is suspect | Motor already swapped; verify replacement insulation |
| Encoder feedback degraded → current-loop ripple → RMS current exceeds fundamental | Medium | High-resolution r0029 trace shows harmonics; r0451 / r0459 error counters elevated | Replace encoder + signal cable; verify DRIVE-CLiQ termination |
| PWM current harmonics not reflected in r0029 | Low–Medium | Oscilloscope on a phase wire vs. r0029; check p1800 (pulse frequency) | Confirm p1800 matches Motor Module rating (4 kHz / 8 kHz) |
| Mechanical load higher than expected after motor swap | Medium | Back-drive shaft by hand; compare holding torque; check coupling alignment | Re-align coupling, replace bearing if grinding |
| Ambient / cooling obstruction | Low (other axes OK) | Compare housing temperature to adjacent motors under same load | Improve ventilation |
| Drive firing circuit / IGBT fault | Low | r0029 reads correctly but motor still overheats; waveform shows spikes | Replace Motor Module (planned) |
| Power cable heat soak — undersized cable raises winding temperature via conduction back through windings | Medium | Voltage drop under load; cable gauge cross-check vs. 6 mm² typical for 1FK7103 at 12 A continuous | Replace with correct Motion Connect cable |
Step-by-Step Diagnostic Procedure
- Capture r0029 high-resolution trace. In STARTER or Startdrive, configure an 8-second trace on r0029[0] with 1 ms sample time. Look for oscillations above 200 Hz that would not appear on the standard HMI 4 ms smoothing filter.
- Compare r0035 (motor temp) to the pyrometer. A 14 K delta during steady-state is within normal expectations (housing lags winding). A delta > 30 K is suspect. A delta < 5 K with the drive reading near the warning threshold indicates the sensor is biasing low.
- Verify p0601 configuration. Confirm p0601 = 1 (KTY84-130). If the wrong sensor type is selected, the drive applies wrong scaling and the temperature reading is meaningless.
- Inspect power and signal cable routing. 1FK7 motors use a hybrid cable that carries U/V/W power, PE, encoder signal pair, and brake pair in one connector. Partial shorts or insulation damage on the signal pair will bias the sensor. Check connector mating surfaces for contamination or bent pins.
- Measure insulation resistance. With the motor disconnected, megger at 500 V on each phase to PE. > 100 MΩ is healthy; 1–100 MΩ indicates moisture/degradation; < 1 MΩ is a fault.
- Check Sensor Module health. r0192 (SBM diagnostic) and the LED pattern on the SBM should show solid green. A flashing red or yellow indicates DRIVE-CLiQ communication errors or sensor wire break.
- Inspect encoder feedback quality. Use r0451 (encoder error counter) and r0459 (encoder diagnostics). Watch for cyclic errors that point to a damaged resolver cable. Replace the encoder cable as a precaution given the user's plan.
- Swap the Motor Module (planned step). Replace the entire Motor Module (catalog number, for example, 6SL3120-1TE23-0AA4 or matching variant) with the correct rating for the 1FK7103-5AF71. Re-commission using STARTER / Startdrive with the electronic nameplate from the new motor.
- Verify thermal steady-state. After re-commissioning, run the axis at the original operating torque for 2 hours. r0035 should stabilize within the class-F continuous rating (typically < 120 °C). External pyrometer reading should be within ±10 K of r0035.
Tuning Checks for Hidden RMS Heating
If the new Motor Module still produces a high winding temperature at low apparent torque, the current loop may be under-tuned for this individual motor. Even a “stable-looking” fundamental current trace can mask higher-order harmonics that contribute to RMS I²R losses without changing the average torque.
Key tuning parameters:
| Parameter | Function | Verification |
|---|---|---|
| p1400.1 | Speed controller enable | Must be set if speed-controlled operation is expected |
| p1460 | Speed controller gain | Compare to factory-loaded value from STARTER commissioning |
| p1462 | Speed controller integral time | Compare to factory-loaded value |
| p1715 | Current controller gain | Compare to factory-loaded value |
| p1717 | Current controller integral time | Compare to factory-loaded value |
| p1800 | Pulse frequency | Must match Motor Module rating; deviating upward reduces current ripple but increases switching losses |
If the controller is "tuned too hot" (excessive Kp, too low Tn) the controller responds to noise with high-frequency current bursts. RMS current rises faster than the HMI display suggests because the smoothing constant filters them out. Capture a high-resolution current trace before declaring the electrical side healthy.
Cable Specifications for the 1FK7 Power/Signal Hybrid Cable
The standard cable for a 1FK7103-5AF71 in continuous duty is Motion Connect 800 (PUR jacket, drag-chain rated) or Motion Connect 500 (PVC jacket, fixed installation). Required gauge for 12 A continuous:
| Cable Variant | Conductor Cross-Section | Continuous Current Rating | Typical Catalog |
|---|---|---|---|
| 6FX8002-5CA01-.... | 1.5 mm² | 12 A (recommended for 1FK7103) | Motion Connect 800 |
| 6FX8002-5CA11-.... | 2.5 mm² | 18 A | Motion Connect 800 |
| 6FX5002-5CA01-.... | 1.5 mm² | 12 A | Motion Connect 500 |
Verify on the cable jacket that the part number matches the 1FK7 connector family. A wrong cable variant is a known cause of sensor bias because the signal pair impedance and the temperature-sensor pinout differ between connector types (M23 vs. M40 vs. hybrid Speed-Connect).
Expected Behavior of Compressed Air as a Workaround
Verification Checklist
- r0035 (winding) stabilizes below 120 °C within 30 minutes at rated load.
- External pyrometer reading on the housing stays within ±10 K of r0035 during steady-state.
- r0029 waveform shows no oscillation > 5 % of fundamental at any speed.
- SBM LED is solid green; no DRIVE-CLiQ diagnostic warnings.
- Encoder error counter r0451 stays at zero over a 24-hour run.
- Compressor at the motor housing is no longer required to keep the axis in production.
Safety Notes
Working on a SINAMICS S120 axis while the drive is live is hazardous. DC bus capacitors retain lethal voltage for up to 5 minutes after mains removal. Always verify DC bus voltage via r0026 and the LED status indicators on the Motor Module before touching motor power connections. A 1FK7 motor's rotor contains rare-earth magnets; during dismounting, keep ferromagnetic tools away from the shaft to avoid pinching. Refer to the SIMOTICS 1FK7 Operating Instructions manual for safe handling.
FAQ
Why does the drive read 98 °C internally while my pyrometer only shows 84 °C on the 1FK7103-5AF71?
The embedded KTY84 sensor measures the hottest point inside the stator end-turns, while the pyrometer measures the housing surface. A 10–20 K gradient during steady-state load is normal. If the delta exceeds 30 K, suspect insulation degradation, power-cable heat soak, or a temperature-sensor bias problem.
How do I map HMI tags K241 and K242 to SINAMICS parameters?
K241 typically maps to r0027 (actual torque, Nm) or r0079 (torque utilization, %). K242 typically maps to r0029 (output current, A RMS) or r0030 (current utilization, %). Always confirm the reference base — a 30 % reading may be referenced to drive rated current, not motor nameplate current. Use STARTER or Startdrive trace to record r0029 directly and remove any scaling uncertainty.
What temperature sensor does the 1FK7103 use and how do I configure it in SINAMICS?
Most 1FK7 motors ship with a KTY84-130 silicon temperature sensor. Configure p0601 = 1 (KTY84) in the SINAMICS drive. If p0601 is left at the default 0 (no sensor) the drive relies entirely on the I²t model, which can mask real overtemperature. A PTC sensor should be configured with p0601 = 2.
Which SINAMICS fault code indicates motor overtemperature?
F07011 = motor overtemperature detected by the I²t thermal model; F07012 = motor overtemperature detected by the physical sensor; A07015 = motor temperature sensor warning. Any of these will trigger drive shutdown once configured via p0612. See the SINAMICS S120/S150 List Manual for fault-code details and recommended response.
Does blowing compressed air on the motor housing actually solve the overtemperature problem?
No. Compressed air cools the housing but does not reduce the winding temperature measured by the embedded KTY84 sensor. The drive will continue to read high winding temperature regardless. Compressed air is a workaround to keep production running while the actual cause — sensor bias, insulation degradation, encoder feedback issue, or IGBT firing problem — is diagnosed and fixed.