System Overview
The SIMODRIVE 611 family is a modular digital servo drive platform. Even when no CNC or PLC is available, the drive remains fully functional because the position/speed control loops are closed inside the drive itself once enabled. The system decomposes into four mandatory subassemblies:
| Module Type | MLFB / Part Range | Function |
|---|---|---|
| Infeed / Line Module (UE) | 6SN11xx-xAxx-x (single-axis) / -xBxx (two-axis supply) | Rectifies 3-phase mains, supplies DC bus (~600/700 V DC) to LT module(s) |
| LT Power Module | 6SN1123-x (1-axis, 3/5/10/15 A) / 6SN1124-x (2-axis) | DC-bus-to-motor inverter with IGBT bridge and braking chopper |
| Control Card (closed-loop) | 6SN1118-0NHx1-x (HR = high-resolution) / -0NJxx (standard) | Speed/position regulator, setpoint inputs, PROFIBUS, RS232, encoder interface |
| Servomotor | 1FK7xxxx-x (synchronous, resolver or absolute encoder) | Rotary actuator; encoder feedback wired back to control card |
Prerequisites
- Hardware stack – UE infeed, one LT power module, one 6SN1118-0NHx1 control card, and the 1FK7 motor mounted with feedback cable installed. Verify the motor current rating is below the LT module IN rating (e.g., 1FK7042 rated 4.1 A RMS on a 5 A LT module).
- SIMOCOM U commissioning software – proprietary Siemens tool, historically downloadable from the Siemens Industry Online Support portal (registration required). Without SIMOCOM U you cannot change the PROFIBUS node address, the setpoint source, or the encoder configuration.
- PC-→-drive cable – RS232 null-modem with a Siemens-specific adapter lead terminating at X421 on the control card (15-pin Sub-D, female).
- Setpoint source – function generator or DAC card capable of true bipolar ±10 V analog output with respect to analog ground (terminal X441 on the control card).
- 24 V enable signals – control of terminals X441 pin assignments for drive enable (NE), pulse enable (OE), and controller enable (RE) by 24 V PLC output.
- DC-bus precharge – verify the infeed module is sized so the LT module LED chain shows the "DC bus ready" state before moving the motor.
Step-by-Step: Driving a 611U from Analog ±10 V
Step 1 – Install SIMOCOM U and Establish RS232 Link
Connect the PC COM port to X421 of the control card. Power up infeed first, then LT module. SIMOCOM U will auto-detect the connected axis (Axis 1 or Axis 2 on a 6SN1124). If the link fails, verify baud rate (default 38 400), then try 9600. Cross-check that the LT module LED chain progresses past the initial "wait for control card" state – a frozen "– – –" indicates a flat-cable or module addressing issue.
Step 2 – Reconfigure Setpoint Source from PROFIBUS to Analog
In SIMOCOM U navigate to Parameter > Drive > Setpoint:
| Parameter | PROFIBUS Default | Retrofit Setting | Effect |
|---|---|---|---|
| PROFIBUS / Analog select | PROFIBUS | Analog (terminal input) | Routes X441 setpoint to speed controller |
| Setpoint smoothing | 0 ms | 5–10 ms PT1 | Reduces noise from hobby DAC |
| Direction reversal polarity | POS = clockwise | Match motor rotation to setpoint sign | Avoids swap of motor leads |
| Speed controller Kp / Tn | Defaults | EEPROM factory values per motor MLFB | Load motor parameters first |
Step 3 – Load Motor Parameters from the Internal EEPROM
The 1FK7 motor's nameplate and tuning parameters are partially stored in the motor's encoder memory and partially in an EEPROM that lives in the resolver/encoder cable. SIMOCOM U reads the motor data block on connection. If the motor is non-Siemens or unknown, manually enter the following into SIMOCOM U under Motor:
- Motor MLFB (e.g., 1FK7042-5AF71-1AH0)
- Continuous stall current I0 (RMS)
- Torque constant KT (Nm/A RMS)
- Number of pole pairs (2 for 1FK7 – 8-pole / 4-pole-pair)
- Resolver offset angle
Step 4 – Wire the Setpoint and Enable Inputs at X441
The terminal block X441 on the 6SN1118-xNHx1 control card exposes the following mandatory signals for stand-alone operation:
| Pin | Signal | Direction | Required Logic |
|---|---|---|---|
| 5 | ANA – (analog GND) | — | Tie to DAC ground, analog shield reference |
| 6 | ANA + (setpoint input, ±10 V) | Input | Bipolar ±10 V proportional to speed |
| 7 | +10 V reference output | Output | Reference voltage, max 5 mA; do not load |
| 8 | NE / drive enable | Input | 24 V high = drive enabled |
| 9 | OE / pulse enable | Input | 24 V high = IGBT firing pulses released |
| Additional inputs: RE / controller enable, ramps, external fault (FEXT) | |||
Step 5 – Apply Enables in the Correct Sequence
- Switch on infeed (DC bus pre-charges).
- Apply 24 V to terminal X441 Pin 8 (NE = drive enable).
- Apply 24 V to terminal X441 Pin 9 (OE = pulse enable).
- Apply controller enable (RE) last. Drive now displays "Operating, n-set follow" mode.
Removing 24 V from OE at any time will directly chop the IGBT gate signals, delivering a braking-stop sequence; this is the safe-stop path. Removing NE puts the drive in "speed-controller-inactive" but may keep the DC-bus hot.
Step 6 – Drive a Slow Verification Move
With a 0 V nominal setpoint, command a small offset (e.g., +0.5 V) and observe the LED chain plus motor shaft rotation. Use the SIMOCOM U oscilloscope page to verify the speed controller has no overshoot. Repeat at –0.5 V to confirm direction. Only then scale up to ±9 V and ±20 V sweeps.
Verification
- LED chain on LT module: sequence should reach "n-set = n-act" steady state within 50 ms of setpoint application.
- Encoder feedback: SIMOCOM U Trace > Actual n should show approximately linear mapping of ±10 V → motor rated speed; e.g., 10 V setpoint on a 1FK7042 (3000 RPM nominal) should produce ~3000 RPM.
- Fault-free operation: confirm that under acceleration no F0xx series alarms are raised; specifically F011 (overspeed) must be avoided by clamping maximum setpoint to motor mechanical limit.
- Brake resistor: during repeated decel cycles, LT module temperature LED should not latch into alarm; chopping resistor needs adequate dissipation headroom for the chosen motor inertia ratio.
Common Fault Codes and Field Remedies
| Alarm | Meaning | Typical Retrofit Cause | Remedy |
|---|---|---|---|
| F011 | Motor overspeed | Analog setpoint clamped too high for motor nmax | Reduce analog gain; simulate maximum expected velocity before enabling OE |
| F015 | Resolver / encoder fault | Feedback cable shield not tied to X411 shell or length mismatch | Verify encoder cable ≤ 50 m, shield bonded at drive end only |
| F021 | DC bus overvoltage during regeneration | No braking resistor sized for retrofit application | Verify chopper resistor mounted; check SH parameters P0190/P0194 |
| F031 | Motor stalled (excessive setpoint vs torque) | Mechanical bind, missing torque parameter | Re-run motor identification in SIMOCOM U |
| F070 | PROFIBUS watchdog timeout | PROFIBUS still active but no host cyclically polling | Disable PROFIBUS entirely in SIMOCOM U; re-route setpoint to ANA |
| F101/104 | Enable logic missing | NE/OE/RE sequencing wrong or control card not in "operating state" after step 4 | Confirm all three enables applied; check parameter P0850 bit field |
Troubleshooting Matrix
| Symptom | Likely Root Cause | Action |
|---|---|---|
| Motor does not torque after enable chain | NE applied but OE missing, or NE/RE logic in SIMOCOM U inverted | Check P0850 and P0851 enable bitmaps; verify both inputs go to 24 V on a multimeter |
| Motor rotates but audible mechanical hum / cogging | Resolver offset not yet learned | Trigger SIMOCOM U automatic commutation find (P1016 = 1) |
| Drive faults immediately on analog > 0.5 V | Setpoint scaling parameter mismatched to DAC gain | Adjust P0400 (setpoint scaling) and re-measure with SIMOCOM U trace |
| Run/Stop randomly under host loop | EMI on analog cable; missing shield bond at X441 GND | Use shielded twisted pair, ground shield at one end only |
| Cannot reach rated RPM at full ±10 V | PROFIBUS scaling still dominant in regulator | Send "Setpoint from ANA = active" command explicitly in SIMOCOM U Operation > Mode |
Mechanical and Electrical Safety Limits
- Maximum DC bus voltage: 700 V DC — never apply analog setpoints until the LT module has cleared its pre-charge state.
- Braking chopper duty: verified per LT datasheet; for retrofit use, derate to 50 % continuous to avoid nuisance trips.
- Resolver cable length: Siemens recommendation ≤ 50 m with specified cable 6FX2001-2 (continuous flex) or 6FX2001-4 (fixed). Longer lengths require repeaters or absolute encoder feedback.
- Analog input protection: the ±10 V input tolerates ±15 V continuous but no reverse polarity or DC injection beyond ±30 V — install a 1 kΩ series resistor for hobby circuit protection.
Approved SIMOCOM U Workflow Summary
- Connect RS232 to X421.
- Read drive and motor data; save a backup with File > Upload.
- Switch Setpoint source to ANA.
- Load motor from internal encoder memory; verify pole pairs and resolver offset.
- Configure enable flags P0850 / enable logic P0851.
- Run automatic controller optimization Operation > Identification.
- Save the parameter set to the control card EEPROM (File > Download); cycle DC bus and re-test.
Can a SIMODRIVE 611U be run without a SINUMERIK CNC or SIMATIC PLC?
Yes. The 611U is a self-contained closed-loop servo drive. With the LT power module, infeed module, control card 6SN1118-0NHx1, and motor wired together, analog ±10 V setpoint at X441 plus 24 V drive, pulse, and controller enable signals are sufficient to run the motor in velocity mode.
Does the 6SN1118 control card accept step/direction inputs natively?
No. The 6SN1118-0NHx1 does not expose dedicated step/direction terminals. Step/direction setpoints are typically delivered via PROFIBUS-DP as a positioning telegram. For hobby CNC retrofits, generate the analog velocity command on the host side and use the drive in velocity mode.
Is SIMOCOM U still available for download?
Yes, from Siemens Industry Online Support, but the requirement is a registered enterprise or developer-level account. Once installed, SIMOCOM U works offline against the drive via RS232 to X421. There is no official open-source substitute for the firmware-level commissioning steps (setpoint source, motor identification, controller optimization).
Which catalog number is the LT module versus the control card?
6SN1118-0NH11-0AA1 is the control card (Version B/C are variants). LT power modules live in the 6SN1123-x (single-axis) and 6SN1124-x (dual-axis) ranges. The control card and LT module must be paired with a 6SN11xx-xAxx-x or -xBxx-x infeed module that powers the DC bus.
What Siemens documentation covers the analog ±10 V wiring?
Section 2.3.1 of the SIMODRIVE 611 universal / universal E, Control Components for Closed-Loop Speed Control and Positioning manual provides the canonical connection diagram for the 6SN1118-0NH11-XAA1 control card and analog ±10 V setpoint wiring at terminal X441.