Configuring Siemens G120 Speed Reference via S7-1200 SINA_SPEED

1. Problem Definition and Solution Strategy

A SINAMICS G120 connected to a SIMATIC S7-1200 via PROFINET is normally driven end-to-end from the PLC: the SINA_SPEED function block feeds control word 1 (STW1) over the PROFIdrive telegram, and the same telegram delivers the speed setpoint (NSOLL) to the inverter. In this application, however, only the digital commands (start, stop, jog, reverse) come from the PLC, while the speed reference must come from a wired potentiometer connected directly to the G120's analog input. No HMI is available, and the operator must be able to vary speed locally at the cabinet door with a 10 kΩ panel-mount pot.

The clean solution exploits the independence between the SINAMICS command source (P0700) and the setpoint source (P1000). The PLC remains the sole source of control words, while P1000 routes the speed reference to the analog input. With Standard Telegram 1 selected, SINA_SPEED only exchanges STW1 and ZSW1, and the drive uses the analog input magnitude (modulated by STW1 bit 11 for direction) as the speed reference. Telegrams 2 or 3 carry NSOLL/NIST setpoint values and would create a conflict with the analog input strategy unless they were deliberately overridden.

2. Prerequisites

Verify the SINAMICS firmware version online in TIA Portal: connect to the drive, open Parameters → All parameters, filter for r0018, and confirm the firmware build before proceeding.

3. Hardware Wiring of the Potentiometer to the G120 Analog Input

The CU240E-2 PN exposes a 0–10 V reference and a differential analog input on the low-voltage terminal block. Wire the potentiometer as a three-terminal voltage divider:

Use shielded twisted-pair cable between the potentiometer and the CU. Ground the shield at the CU end only (terminal 2 or the shield clamp on the control unit housing). Maximum recommended run length for a 0–10 V signal is 30 m; beyond that, switch to a 4–20 mA current loop with a 500 Ω shunt resistor to avoid voltage drop and noise pickup.

The analog input on the CU240E-2 PN has an input impedance above 100 kΩ in voltage mode, so the 10 kΩ potentiometer draws under 1 mA from the 10 V reference — well below the 10 mA terminal rating. If you must use a higher-value pot (e.g., 47 kΩ for low-power applications), increase P0757[0] and P0759[0] accordingly to match the scaled input range.

4. SINAMICS G120 Parameter Map for Analog Speed Reference

The following parameters must be written to the drive. They are accessible via TIA Portal → drive device → Parameters → Online, via the BOP-2/IOP-2, or via the SINA_PARA function block from a PLC routine.

When P1000[0] = 2, parameter P1070[0] defaults to r0755[0] automatically. If you previously changed P1070[0] to a non-AI source, you must re-assign it to 755.0 in the BICO editor. Without this re-assignment, the analog input is sampled but never reaches the main setpoint pipeline.

5. Configuring the Drive in TIA Portal

1. Open the TIA Portal project containing the S7-1200 CPU and the SINAMICS G120 device.
2. If the G120 is not yet in the project, install its GSDML first: Options → Manage general station description files (GSD), browse to the GSDML, and confirm.
3. Add the SINAMICS G120 from the hardware catalog under Drives & Starters → SINAMICS → SINAMICS G120, matching the order number of your CU (e.g., 6SL3246-0BA22-1FA0).
4. Drag the drive onto the PROFINET subnet of the CPU. Assign a unique IP address (e.g., 192.168.0.20) and a PROFINET device name (e.g., "g120-cu240e"). The device name must match what you assign later with the Topology Editor or PRONETA.
5. Open the drive's device view. Under Device configuration → PROFINET interface → Telegram configuration, insert Standard Telegram 1 (2 PZD in / 2 PZD out). Do not insert Standard Telegram 2 or 3 — they include NSOLL/NIST, which would conflict with the analog setpoint strategy unless P1000 is re-routed.
6. Compile the project (Ctrl+B) and download the hardware configuration to the CPU and the drive. Confirm the drive accepts the new name by checking the BF LED transitions from red to off.

The Standard Telegram 1 assignment delivers STW1 (2 bytes) from the PLC to the drive and returns ZSW1 (2 bytes) plus the actual speed NIST (in NIST mode) back to the PLC. The cyclic I/O exchange updates every PROFINET bus cycle, typically 1–4 ms on a 1 ms send clock.

6. SINA_SPEED Block Integration

The SINA_SPEED block (FB285 in older library versions, FB30002 in TIA V17) from the SINAMICS blocks library is the standard interface to a SINAMICS drive over PROFINET. Add it to a function block or OB in the S7-1200 program and wire the inputs as follows:

Inputs

Outputs

Minimum required F-block call (SCL example for OB1):

// One-time initialization in OB100 / startup
g120_sina.ConfigAxis.RefSpeed  := 1450.0;     // motor rated speed
g120_sina.ConfigAxis.MaxSpeed  := 1500.0;     // upper clamp
g120_sina.ConfigAxis.MinSpeed  := 0.0;        // lower clamp
// Cyclic call in OB1
g120_sina.LADDR                 := "G120_CU240E".HW_ID;
g120_sina.Enable                := start_cmd AND NOT estop;
g120_sina.FaultAck              := reset_pulse;
g120_sina.SpeedSetpoint         := 0.0;       // drive ignores, P1000 = analog
g120_sina.CtrlFlags.Reverse     := dir_reverse;
g120_sina.CtrlFlags.EnableJogPos := jog_fwd;
g120_sina.CtrlFlags.EnableJogNeg := jog_rev;
g120_sina();
running     := g120_sina.AxisStatus.Enabled;
speed_rpm   := g120_sina.ActualSpeed;
fault_active := g120_sina.AxisStatus.Fault;

7. Setpoint Source Routing and Direction Control

With Telegram 1 selected and P0700 = 6 (PROFINET), STW1 from SINA_SPEED drives ON/OFF1, OFF2, OFF3, enable ramp generator, enable setpoint, ramp-function-generator enable, jog bits, and the reverse bit. The setpoint pipeline inside the drive runs as follows:

1. Analog input AI0 is sampled and normalized to a percentage (0–100 %) by P0756–P0760; the live value is exposed at r0755[0].
2. P1070[0] = r0755[0] routes the AI0 percentage into the main setpoint connector.
3. P1000[0] = 2 confirms "Analog setpoint 1" as the main setpoint source. P1070 then defaults to r0755[0] when P1000 is set to 2.
4. The setpoint passes through the ramp-function generator (P1120 ramp-up, P1121 ramp-down).
5. P1080 (min) and P1082 (max) clamp the setpoint.
6. Direction is taken from STW1 bit 11 (set by SINA_SPEED Reverse input). With a unipolar 0–10 V potentiometer, the magnitude is positive; bit 11 reverses the sign.

The decoupling of command source (P0700) and setpoint source (P1000) is one of the most useful features of the SINAMICS platform. It allows a SINA_SPEED-based PROFINET control loop to coexist with a fully analog speed reference — a configuration commonly found in retrofit projects where a new PLC is being added but the operator interface is being retained.

8. Speed Scaling, Ramps, and Limits

With the default AI scaling (0 V = 0 %, 10 V = 100 %), the motor speed tracks the potentiometer between P1080 and P1082. Use the formula:

n_setpoint (rpm) = P1080 + (P1082 − P1080) × (V_pot / 10 V)

Example: P1080 = 0, P1082 = 1450, V_pot = 5 V → n_setpoint = 0 + (1450 − 0) × (5/10) = 725 rpm.

Practical ramp settings:

• P1120 (ramp-up): 5–20 s for general-purpose machinery. Conveyor belts: 5 s. Centrifugal pumps: 10 s. Fans: 15–30 s.
• P1121 (ramp-down): equal to or slightly longer than P1120 to avoid regenerative faults on low-inertia loads.
• P1135 (OFF3 ramp): typically 3 s for fast-stop compliance with category 1 stops.

Set P1082 to the motor's rated speed to get a 1:1 potentiometer-to-speed ratio. If a coarser ratio is desired (e.g., to use only 50 % of the pot's rotation for full speed), scale P0760[0] below 100 % or reduce P1082. The lower clamp P1080 also doubles as a creep-speed minimum if you want the pot to never reach zero RPM.

9. PROFIdrive Telegram and Drive State Machine

The PROFIdrive profile (PNO order no. 3.172) defines the drive state machine that SINA_SPEED implements through STW1 bit manipulation. The key states for this application are:

ZSW1 mirrors the state back to the PLC. The bit assignment in ZSW1 enables the SINA_SPEED block to populate its AxisStatus output structure without any custom decoding. Always read ZSW1 in trace mode during commissioning to confirm the state transitions follow your Enable and FaultAck inputs.

10. Commissioning and Verification

1. Power up the drive. Verify there is no active fault (r2139 bit 3 should be 0). The drive's RDY LED should be solid green; the BF LED should be off.
2. Establish PROFINET connection. Confirm the BF (bus fault) LED on the CU is off and the RDY LED is solid green. The LINK LED on the PROFINET port should be steady when the cable is connected.
3. From TIA Portal, go online with the drive and confirm that SINA_SPEED has built a clean cyclic link: AxisStatus.ReadyToOperate should be TRUE after Enable is set.
4. Set Enable = TRUE from the PLC. Confirm the motor begins to turn at zero speed (P1080). Slowly rotate the potentiometer; speed should rise linearly to P1082.
5. Toggle Reverse via SINA_SPEED CtrlFlags.Reverse. Confirm the motor direction reverses while speed tracks the potentiometer.
6. Toggle EnableJogPos and EnableJogNeg. Confirm the motor runs at the configured fixed jog speed.
7. Trigger SlowStop and FastStop. Confirm the motor stops within the configured ramp times (P1121 for slow, P1135 for fast).
8. Force a fault (e.g., trip OFF2 by removing Enable while running). Confirm the drive faults, sets ZSW1 fault bit, and requires FaultAck to clear.
9. When everything is verified, set P0971 = 1 to write all parameters to the drive's non-volatile memory. Wait for the acknowledgment (the BOP-2 displays "busy" briefly, then returns to the standard display).

11. Troubleshooting Matrix

FAQ