Configuring Revolution Speed on Siemens SIMATIC S7 Motion Control

Configuring Revolution Speed on Siemens SIMATIC S7 Motion Control

Rotational velocity (revolution speed) is a fundamental setpoint on every Siemens SIMATIC S7 motion axis. Whether the project is a winding reel, a flying shear, a rotary indexing table, or a coordinated print-mark registration, the engineering challenge is the same: how to configure the velocity initially, how to change it cleanly at runtime, and how to verify it under load without overshooting the drive. This reference consolidates the parameter mapping, technology object (TO) configuration, runtime-modification paths (including synchronous actions), and diagnostic checks that separate a working axis from a faulted one.

Unit Conversion and Engineering Data

Inside a technology object the user sees one of two velocity representations depending on the selected unit system. Mixing them is the single most common commissioning error on rotary axes.

The load-side shaft speed is derived from the motor speed and the gearbox ratio. Always size n_motor against the drive's nominal speed (n_nominal) and derate by 80% to leave headroom for acceleration transients:

n_motor_set  = (n_load · i_gearbox) / (i_load_gearbox)
where:
  n_motor_set  = motor reference speed [rpm]
  n_load       = required load revolution speed [rpm]
  i_gearbox    = gear ratio (motor-revolutions : load-revolutions)
  i_load_gearbox = additional output-stage ratio (default 1)

The peak motor torque required to reach n_set inside the configured ramp time is:

T_peak = J_total · Δω / t_acc + T_load
where:
  J_total  = J_motor + J_gearbox + J_load / i^2 [kg·m^2]
  Δω = 2π · (n_set - n_act) / 60 [rad/s]
  t_acc    = configured acceleration time [s]
  T_load   = steady-state torque demand [Nm]

If T_peak exceeds 1.6 × T_nominal, the Siemens drive will start derating and the configured revolution speed will not be achieved. Verify against the SINAMICS S120 parameter r0345 (power unit overload capability).

Prerequisites

1. Hardware: SIMATIC S7-300 with CPU 315T-2 DP / 317T-2 DP / 317TF-2 DP (or compatible IM 153 / ET 200S-based T-controller). For S7-400, CPU 417T. Standard CPU 315-2/317-2 cannot host technology objects; the T-suffix is mandatory.
2. Software: SIMATIC Manager Step 7 V5.5 SP4 or later, S7-Technology library V4.2 (or matching TO firmware). TIA Portal V17 with S7-1500T for forward migration.
3. Firmware: T-CPU firmware ≥ V4.2 supports 8 axes per interface; ≥ V4.3 unlocks camming (MC_CamIn). Confirm in PLC → Module Information → Firmware.
4. Drive side: SINAMICS S120 with Telegram 103/105/106 configured in HW Config, or third-party drive on PROFIdrive (DP/PN) using Telegram 1 / 2 / 3.
5. Encoder: Incremental encoder on the load side (preferred for revolution-speed accuracy) or SSI absolute. Encoder resolution typically 2²⁰ = 1,048,576 incr/rev for high-precision winding.
6. Safety: STO / SS1 wiring completed before any velocity test. Confirm F-LED off on the T-CPU and the drive's PROFIsafe channel reporting 0x00000000.

Hardware Platform Selection

Synchronous actions are bound to the IPO cycle (OB 61/OB 62 on T-CPU, OB 67/68 on S7-1500T). Their priority level (16-25) sits above OB 1, which is why they remain deterministic even under heavy cyclic load.

Configuring Revolution Speed via Technology Objects

The technology object (TO) is the canonical place to define the axis velocity envelope. Open the TO → "Configuration" dialog in SIMATIC Manager and validate the five parameters below before the first download.

Step 1: Mechanical parameters

1. Open SIMATIC Manager → S7 Program → Technology Objects → Axis → Configuration.
2. Select "Axis type" = Rotary.
3. Set "Increments per revolution" (load-side). For a 1024-line encoder with x4 evaluation: 1024 · 4 = 4096.
4. Set "Gear ratio" (motor : load). Example 4.0 for a 4:1 reducer.
5. Set "Position range" = 0 to 360000 ° (or 0 to 1000 rev) depending on the unit system selected.

Step 2: Drive and encoder assignment

1. HW Config → T-CPU properties → Motion Control tab → assign the PROFIdrive telegram (Tele 103 for SINAMICS, Tele 2 for Micromaster).
2. In the axis TO → "Drive → Interface", select the configured drive and the encoder slot (typically Slot 0 / Encoder 1).
3. Set the drive reference speed (n_ref) equal to the motor's rated speed → p2000 on SINAMICS. This is the value that maps 100% of the drive's velocity setpoint.

Step 3: Velocity, acceleration and jerk

Step 4: Compile and download

1. Right-click the TO → Compile.
2. Download the generated blocks DB-SET (axis setpoint DB) and DB-IID (axis instance) to the controller.
3. Confirm TO online; the field "Status / Standstill" must appear before MC_Power is issued.

Runtime Modification via SFB Calls

The PLCopen-style function blocks from the "SIMATIC Technology" library are the de-facto runtime API. The most common MC_*** block for setting revolution speed at runtime is MC_MoveVelocity.

FUNCTION_BLOCK FB_RevolutionSpeed
VAR
  Axis        : TO_Axis;                 // axis instance handle
  fbPower     : MC_Power;                // axis enable
  fbMoveVel   : MC_MoveVelocity;         // velocity motion FB
  fbRead      : MC_ReadActualVelocity;   // diagnostic feedback
  fVelocityRpm: LREAL := 0.0;            // setpoint in rpm
  bEnable     : BOOL := FALSE;
  bOn         : BOOL := FALSE;
END_VAR

// 1. Power-up
fbPower(Axis := Axis, Enable := TRUE, EnablePositive := TRUE, EnableNegative := TRUE, Override := 100.0);

// 2. Latch new speed value into the FB
fbMoveVel(Axis := Axis, Execute := bOn, Velocity := fVelocityRpm, Acceleration := 50.0, Deceleration := 50.0, Jerk := 100.0);

// 3. Read back actual velocity (diagnostic)
fbRead(Axis := Axis, Enable := TRUE, Velocity => rlActRpm, ActualDirection => bDir);

Key input behaviour:

• Velocity unit must equal the TO's configured unit. Set once during commissioning, never changed at runtime.
• Acceleration / Deceleration are denormalized values. Internally these are converted to the axis's configured units (deg/s², rad/s², or rev/min/s depending on TO selection).
• Override (between 0 and 100) operates on top of the Velocity input. Use it instead of re-triggering MC_MoveVelocity for jog-style ramped changes. Applying Override less than 25 abruptly trips the drive on most S120 firmware ≤ V4.3.

For true runtime speed changes triggered by a process variable (e.g. line speed on a winder), use MC_MoveVelocity with a cyclic rewrite of the Velocity input. Do not pulse Execute each scan - this causes a toggle restart.

Runtime Modification via Synchronous Actions

Synchronous actions are real-time callbacks evaluated inside the IPO. They execute in less than 100 µs, making them the preferred channel for closing the velocity loop on encoder-interrupts or for cutting the speed based on a high-speed digital flag.

Syntax

{OB-mask | condition} action_list

Example - cap revolution speed during emergency pull

// In OB 61 (IPO1, 500 µs)
SA1: {DLY 0, "Axis1.PositionData.ActualVelocity" > 3000.0} 
        "Axis1.SetpointData.VelocityOverride" := 60.0;
        "DB_State.EmergencyTrip" := TRUE;

SA2: {"DB_State.CoilFree"}    
        "Axis1.SetpointData.VelocityOverride" := 100.0;

Rules of use

1. Synchronous actions may only access technology-object data structures (Axis1.SetpointData.*, Axis1.PositionData.*) and DB memory. Direct I/O access from a synchronous action triggers a compile error.
2. Actions triggered by interrupt OBs (OB 40-OB 47) take precedence over the IPO cycle.
3. Each synchronous action consumes a fixed program slot - the TO inspector reports the count in use. CPU 317T-2 DP supports 64 simultaneous actions; CPU 315T-2 DP supports 32.
4. Use {mode-condition} syntax (S, R, J, A, N) for set/reset/jump/assignment/edge. J is the only construct that can branch within a sync action.

The Siemens "SIMATIC S7-300 / S7-400 Motion Control - Programming and Operating Manual" (edition 11/2006) documents the precise scoping rules for synchronous actions and the priority interaction with OB 1 (subordinate). When the controller was not able to modify the PLC program on-site, the engineered workaround was to push the velocity transition logic into synchronous actions so that changes could be made online inside the loaded binary.

Drive-Side Velocity Mapping

Every technology object writes a normalized setpoint of [-100.0%, +100.0%] across the PROFIdrive cyclic channel. The drive converts that into an actual speed using n_set_drive = n_ref · setpoint/100. Mismatch between TO unit system and SINAMICS reference speed produces an apparent "bug" where the configured revolution speed is wildly off.

Verification and Diagnostics

1. Static check: With drive de-energized but TO online, force the Velocity override to 50.0 and read Axis1.SetpointData.VelocitySetpoint. It must reflect exactly half of the configured nominal velocity.
2. Trace: Open the T-CPU web server ("Diagnostics") and trigger a velocity step from 25% to 100%. Confirm the rising edge reaches 95% of the target within the configured acceleration window ± 5%.
3. Overshoot check: Step change from 0 to 100%. Use MC_ReadActualVelocity to log both Setpoint and Actual. Overshoot above +5% of target indicates Jerk limit too low or drive velocity regulator P-gain too high (p1461).
4. Steady-state ripple: Run at nominal speed for 60 s. The standard deviation of ActualVelocity must be ≤ 1% of n_set; otherwise check encoder coupling (resolver wobble, broken tooth) or drive smoothing time constant (p0045 ≤ 4 ms on S120).
5. Follow-up error: Set Axis1.DynamicLimits.FollowingErrorTolerance to 5% of n_max. The axis must never report FollowError during a 10-minute no-load test. Acceptance for the winder is ≤ 1% (over-tensioned web).

Online Inspection - Repeat Last Method

Before leaving site, document the active values. Insert the snippet below into OB 1:

CALL "MC_ReadActualVelocity" (
  Axis        := Axis1,
  Enable      := TRUE,
  Velocity    := vAct_1,
  ActualDirection := diDir_1
);

CALL "MC_ReadSetpoint" (
  Axis        := Axis1,
  Enable      := TRUE,
  Velocity    := vSet_1,
  Acceleration:= aSet_1
);

// Dump to an HMI tag every 100 ms
   "HMI_DB".Main.VelAct    := vAct_1;
   "HMI_DB".Main.VelSet    := vSet_1;
   "HMI_DB".Main.VelDir    := DINT_TO_INT(diDir_1);

Capture a 30 s trace. The Setpoint and Actual curves must overlay within ± 2% of n_nominal. Persistent gap > 5% implies a drive-side bandwidth mismatch that no PLC-side tuning can fix.

Troubleshooting Matrix

Migration to TIA Portal V17/V18

When upgrading a T-CPU line to S7-1500T or moving the project to TIA Portal:

1. Export the TOs from SIMATIC Manager as *.xml using the migration tool.
2. Import under TIA → Options → Migrate Project.
3. Re-check the velocity unit because TIA defaults to mm/s even on rotary axes. Force 1/min before first download.
4. MC_Power / MC_MoveVelocity / MC_Home map 1:1 from SIMATIC Technology to PLCopen blocks. Path: Bibliotheks-Zugriff → PLCopen MC.
5. Synchronous actions become "Motion Control Tasks" - same priority scheme, but configured as a separate OB (TO-specific Task).
6. Verify that the existing PROFIdrive telegram still matches; TIA names them explicitly via the device configuration.

Field-Proven Best Practice

• Lock the velocity unit system at the TO level before any 5-minute project review. Document the choice in the Functional Specification and freeze it as a guideline for the project.
• Never write to the TO instance DB from a cyclic OB with a low priority; doing so rips the IPC handshake and produces F00262 / axis error 108.
• For coordinated clusters, propagate speed changes via the master axis' SetpointData.VelocitySetpoint to ensure the slave's IPCB shares the same time base.
• Keep one real-time loop in OB 1 reading the actual velocity for logging. Drive traces are useless during warranty claims when the PLC has the only timestamp.
• Add a permissive (life-bit) wiring before each MC_Power. Never enable the drive on a permissive that is true for less than 3 PLC cycles.

Revision Log

Frequently Asked Questions