Configuring SINAMICS G120 CU250S-2 HTL Speed Control with S7-1500

The SINAMICS G120 modular drive system paired with the CU250S-2 control unit and an HTL incremental encoder provides a deterministic, encoder-closed-loop speed-control platform for a continuously running conveyor driven by a SIMATIC S7-1500 PLC. The CU250S-2 supports universal vector control with encoder feedback, making it suitable for any G120 drive application with or without encoder feedback. This reference covers drive selection, Telegram 2/3 selection, encoder wiring, TIA Portal V13 SP1 configuration, and commissioning verification.

System Overview

The complete system comprises:

• SIMATIC S7-1500 CPU (e.g., CPU 1515-2 PN or CPU 1516-3 PN/DP)
• SINAMICS G120 power module (PM240-2, PM250, or PM330)
• CU250S-2 control unit (PROFINET or PROFIBUS variant)
• HTL incremental encoder on motor or load shaft (1024 PPR typical)
• Three-phase squirrel-cage induction motor
• STARTER or Startdrive commissioning tool

CU250S-2 Control Unit Variants and Ordering Data

The CU250S-2 control unit is available in two fieldbus variants. Both expose the same encoder interface, so the choice is driven by the fieldbus used for PLC integration.

For PROFINET-based S7-1500 communication, select the PN variant. Common firmware versions deployed in 2020-2026 plants are V4.5, V4.6, and V4.7. Install the latest service pack (e.g., V4.7 SP10 or later) to obtain functional and security patches. The full ordering data and accessory list are documented in the SINAMICS G120 with CU250S-2 List Manual.

HTL Encoder Interface Specifications

The encoder interface is brought out on the 15-pin Sub-D connector X2100 on the front of the CU250S-2. The interface accepts single-ended or bipolar 24 V push-pull signals. Encoder type is selected with parameter p0400 (1 = HTL, 2 = TTL/SSI).

Use 4x evaluation (p0430.13 = 1) to quadruple the effective resolution. For example, a 1024 PPR encoder yields 4096 counts per revolution at the drive level.

Startdrive vs STARTER: Commissioning Tool Selection

Startdrive is integrated into TIA Portal and is the recommended tool for new S7-1500 + G120 projects. STARTER remains supported for trace recordings, firmware updates on older control units, and projects with no S7-1500.

Recommendation: For this application, install Startdrive in TIA Portal V13 SP1 along with the matching Hardware Support Package (HSP) for SINAMICS G120 / CU250S-2. STARTER is only required if you need advanced trace functions or are updating firmware on a control unit that is not yet supported by the installed HSP.

PROFIdrive Telegram Selection

The PROFIdrive telegram defines the cyclic process data (PZD) layout exchanged between the S7-1500 and the drive. The choice of telegram is driven by the application requirements and whether S7-1500 Motion Control (MC_) blocks will be used.

For a free-running conveyor with encoder-closed-loop speed control, Standard telegram 2 is the conventional choice. It provides:

• STW1 (control word 1): drive enable, OFF1/OFF2/OFF3, ramp-function generator control, fault acknowledge
• NSOLL_A (speed setpoint A): 16-bit normalized setpoint, range -16384 to +16384 (0x4000 hex = motor rated speed)
• ZSW1 (status word 1): drive ready, fault, run-up, setpoint-actual deviation within tolerance, actual speed reached
• NIST_A (actual speed A): 16-bit normalized actual speed
• STW2 / ZSW2: extended control and status (sign-of-life, additional status bits)

Use Telegram 3 or higher if:

1. S7-1500 Motion Control (MC_) blocks such as MC_Power, MC_MoveVelocity, MC_Home are to be used.
2. The application requires 32-bit encoder position feedback in the cyclic PZD (e.g., for synchronization of multiple drives).
3. Dynamic Servo Control (DSC) is required for high-dynamic applications (less likely on a conveyor).

Why Telegram 2 Is the Correct Choice for a Free-Running Conveyor

Telegrams 3, 5, 103, 105, and 106 enable the drive-internal position controller. For a conveyor that never stops, the position controller is typically not desired because:

1. Position-controlled telegrams are designed for positioning axes and may inject position corrections during steady-state speed operation.
2. Telegram 2 keeps the drive in pure speed control (closed-loop vector control with encoder, p1300 = 21), which is the natural control mode for a continuously running conveyor.
3. Position information can still be obtained via acyclic parameter access (r0480 encoder count, r0482 absolute position) or by mapping a free PZD word to the encoder count using a free telegram such as 110.

If the application needs MC_ blocks from the S7-1500, use Telegram 3 and configure the drive in TIA Portal as a positioning axis under Technology Objects > TO_Axis_PTO (with PROFIdrive) or TO_SynchronousAxis.

Telegram 2: PZD Layout and Bit Mapping

Output (PLC → Drive)

Input (Drive → PLC)

Motion Control (MC_) Blocks and Telegram Compatibility

The S7-1500 motion control library (e.g., MC_Power, MC_MoveVelocity, MC_Home, MC_Reset, MC_ReadParameter) requires a PROFIdrive telegram that contains a position actual value (G1_XIST) and, for positioning, a position setpoint (G1_SOLL). Only telegrams 3, 5, 103, 105, and 106 expose these signals. Telegram 2 does not include any position data, so MC_ blocks cannot be used with it.

Decision matrix:

• If the application needs only speed control and the position can be derived by integrating the actual speed, integrate NIST_A in the PLC, or read the encoder raw value from r0480 via acyclic parameter access. Use Telegram 2.
• If S7-1500 MC_ blocks are required (e.g., for a synchronized line of multiple drives, or for S7-1500-based homing), use Telegram 3 or Telegram 5 with DSC for the highest dynamic response.

Step-by-Step Configuration in TIA Portal

Prerequisites

• TIA Portal V13 SP1 (or later) installed with the Startdrive option
• Hardware Support Package (HSP) for SINAMICS G120 / CU250S-2 installed (matching TIA Portal version)
• SIMATIC S7-1500 CPU with PROFINET interface (PN variant of CU250S-2 required for PROFINET)
• CU250S-2 PN control unit with firmware V4.5 or later
• HTL incremental encoder, 24 V bipolar, with shielded cable

Procedure

1. Open TIA Portal and create a new project. Add the S7-1500 CPU under Devices & Networks.
2. Open the Hardware Catalog and navigate to Drives > SINAMICS > G120 > Control Units > CU250S-2 PN. Drag the drive to the PROFINET network of the CPU. TIA Portal automatically assigns a device name and IP address (e.g., 192.168.0.10).
3. Open the drive device configuration. Under Properties > PROFINET interface > Telegram configuration, select Standard telegram 2.
4. Note the automatically assigned I/O addresses (e.g., PQW 256 to PQW 262 for output, PIW 256 to PIW 262 for input). These are the addresses used in the PLC program.
5. Assign a PROFINET device name to the drive (e.g., "g120-conv1") via Online > Assign PROFINET device name. The device name must match the configured name in the TIA Portal project.
6. Open the drive's parameter view and run the basic commissioning wizard: enter motor nameplate data, select encoder type = HTL, enter pulses-per-revolution (e.g., 1024), set the application class to "Speed control with encoder".
7. Run motor identification (p1900 = 2 for static, p1900 = 1 for rotating) and speed controller auto-tuning (p1960 > 0).
8. Compile and download the TIA Portal project to the S7-1500 CPU.

Key Drive Parameters for HTL Encoder Configuration

PLC Programming: S7-1500 to G120 Communication

For Telegram 2, the S7-1500 exchanges 4 PZD words in each direction. Define a PLC data type (UDT) for clarity and use direct peripheral I/O writes/reads or the Siemens library block SINA_SPEED (FB 285).

UDT Definition (SCL)

TYPE UDT_G120_Telegram2 :
STRUCT
    STW1    : WORD;   // Output word 1: control word 1
    NSOLL_A : INT;    // Output word 2: speed setpoint (normalized)
    STW2    : WORD;   // Output word 3: extended control
    unused  : WORD;   // Output word 4: not used in telegram 2
END_STRUCT;
END_TYPE;

TYPE UDT_G120_Telegram2_In :
STRUCT
    ZSW1    : WORD;   // Input word 1: status word 1
    NIST_A  : INT;    // Input word 2: actual speed (normalized)
    ZSW2    : WORD;   // Input word 3: extended status
    unused  : WORD;   // Input word 4: not used in telegram 2
END_STRUCT;
END_TYPE;

Setpoint Scaling

NSOLL_A is normalized such that 0x4000 (16384 decimal) corresponds to the reference speed p2000. To command 50% of rated speed, write 0x2000 (8192). To command full reverse, write 0xC000 (-16384). The sign and magnitude are defined in the PROFIdrive profile.

// SCL: enable drive and command 50% speed
"DB_Drive".STW1    := 16#047E;   // OFF1, OFF2, OFF3 released; enable; ramp enable; no fault ack
"DB_Drive".NSOLL_A := 8192;      // 50% of p2000
"DB_Drive".STW2    := 16#0000;
"DB_Drive".unused  := 16#0000;

// After STW1 = 0x047E, set STW1 = 0x047F to latch ON (rising edge on bit 0)
// To command run: STW1 := 16#047F; (bits 0,1,2,3,4,5,6,10 = 1)
// To fault-ack: pulse STW1 bit 7 to 1 (0x04FF then 0x047F)

Using SINA_SPEED (FB 285)

Siemens provides a ready-made function block SINA_SPEED (FB 285, in the SINAMICS library) that wraps Telegram 2 and Telegram 3 control/status. For applications with multiple drives, using SINA_SPEED reduces programming effort and ensures consistent bit-level handling.

HTL Encoder Wiring (X2100)

Wire the HTL encoder to the 15-pin Sub-D connector X2100 on the front of the CU250S-2. Pin assignment (see SINAMICS G120 with CU250S-2 List Manual for the full pinout):

For a 3-wire single-ended HTL encoder, connect only A, B, N (and 24 V supply); leave the inverted channels (A*, B*, N*) open. For industrial environments with VFD-induced noise, use the bipolar (6-wire) connection with shielded twisted-pair cable (e.g., LiYCY 4x2x0.34).

Commissioning Procedure

1. Apply 24 V control voltage and 400 V (or 480 V) main supply. Verify the CU250S-2 LED is solid green (RUN) and the PROFINET LEDs are flashing or solid green.
2. In TIA Portal, go online to the drive and run the basic commissioning wizard in Startdrive: select application class = Standard Drive Control (Speed), enter motor nameplate data, select encoder type HTL (p0400 = 1), enter pulses per revolution (p0408).
3. Set the application parameters: ramp-up time p1120, ramp-down time p1121, reference speed p2000, and speed setpoint source p1500 = 6 (PROFIdrive).
4. Run the motor identification: p1900 = 2 (motor data identification, standstill) and p1960 > 0 (speed controller optimization, requires the motor to spin unloaded or in a safe state).
5. Download the configuration to the S7-1500 and assign the PROFINET device name to the drive.
6. From the PLC, set STW1 = 0x047E (basic enable) and NSOLL_A = 2000 (~12% speed). Confirm the drive accelerates to the setpoint. Verify ZSW1 bits 0, 1, 2 = 1 and bit 10 = 1 (f or n reached).
7. Increment NSOLL_A in steps (e.g., 0x1000, 0x2000, 0x3000, 0x4000) and verify smooth ramp behavior and zero steady-state error.
8. Trigger a fault simulation: disconnect the encoder, command a setpoint, and verify that the drive generates an encoder fault (F3xxxx) and that ZSW1 bit 3 = 1 in the PLC.

Verification Checklist

Troubleshooting Matrix

Position Feedback Without Telegram 3

If Telegram 2 is used and the application needs to know the conveyor position, several approaches are available:

1. Read the encoder actual count via acyclic parameter access: r0480[0] returns the raw encoder count. Use RDREC/WRREC or the SINA_PARA block from the SINAMICS library.
2. Read the absolute position after homing: r0482[0] returns the absolute position in LU (length units) once a homing procedure has been performed.
3. Configure a free telegram (102, 103, 110, or 111) and map the encoder count to a free PZD word for cyclic transmission. For example, configure Telegram 110 and set p2051[x] = r0480[0] for the 32-bit encoder value to be transmitted in PZD words 3 and 4 of the input.
4. Integrate NIST_A in the PLC over time. NIST_A is a 16-bit normalized value; sample it at a fixed PLC cycle time (e.g., 10 ms) and accumulate. This approach is less precise but avoids acyclic parameter access.

Typical Application Class and Control Mode

Startdrive's basic commissioning wizard offers several application classes. For a free-running conveyor with HTL encoder, select:

• Application class: Standard Drive Control
• Control mode: Speed control with encoder (p1300 = 21, encoderless = 0)
• Setpoint source: PROFIdrive telegram 2 (p1500 = 6)

This configuration yields a closed-loop vector speed control with a torque limit (p1520, p1521) and a ramp-function generator at the drive. The S7-1500 controls enable, setpoint, and fault acknowledge via the PROFIdrive cyclic data, while the drive handles torque limiting, ramp generation, and current control locally.

Safety Integration (STO)

The CU250S-2 includes Safe Torque Off (STO) as a standard safety function. STO is hardwired via terminals on the control unit and can be used independent of the PROFIdrive communication. For applications requiring a higher safety level (SS1, SS2, SLS, SDI), use the CU250S-2 with a fail-safe PLC (e.g., CPU 1515F-2 PN) and configure PROFIsafe telegrams on a separate slot.

Standards and PROFIdrive Profile

The PROFIdrive profile is maintained by PROFIBUS & PROFINET International (PI) and is implemented by Siemens in all SINAMICS drives. The current profile version (V4.2 as of 2024) defines standard telegrams 1-106 and the BICO interconnection rules. The conformance classes CC1-CC4 are relevant for different drive types:

• CC1: standard drives (G120 with CU250S-2 fits here)
• CC3: single-axis positioning (telegram 3, 5, 103, 105)
• CC4: synchronized axes with DSC (telegram 5, 105, 106)

Refer to the SINAMICS G120 with CU250S-2 Operating Instructions and the PROFIdrive Profile (PI) for normative details.

FAQ