Sinamics vs Simotion: What's the Difference?

July 21, 2026 • PLC Department Tech Team • 8 min read

Siemens has two product families that show up in the same machine cabinet, do overlapping things, and confuse even experienced engineers: Sinamics and Simotion. Both deal with motors and motion. That's where the similarity ends.

Quick Answer

Sinamics is a drive platform — it converts AC power into controlled motor output. Simotion is a motion controller — it runs coordinated multi-axis sequencing, cam profiles, and synchronization logic on top of (or instead of) a PLC. Most machines need Sinamics; only machines with complex coordinated motion need Simotion.

⚠️ Safety First

Sinamics drives store lethal DC bus voltage after power-down. Before any physical work on a drive or motion controller, follow full LOTO, wait for the DC bus discharge indicator to clear, and verify voltage with a calibrated meter. Discharge times vary by drive size — check the specific unit's documentation before touching terminals.

What Is Sinamics?

Sinamics is Siemens' family of variable frequency drives (VFDs) and servo drives. Its job is straightforward: take incoming AC power, rectify it to DC, invert it back to controlled AC, and spin a motor at the speed and torque you command. Sinamics handles everything from basic pump and fan control up to high-performance servo axis control.

The family covers several series. The Sinamics G drives target general-purpose applications — conveyors, pumps, fans, compressors — where you need speed control but not tight position loops. The Sinamics S series steps up to servo and vector control for applications demanding fast torque response, position holding, and synchronized multi-axis work. Within the S series, the S120 is the workhorse for multi-axis servo systems in packaging, printing, and material handling.

What Is the Sinamics S120 Specifically?

The S120 is a modular, booksize or chassis-format servo/vector drive system. A single Control Unit (CU) connects to one or more Motor Modules (the inverter stages) sharing a common DC bus. That common bus architecture means energy regenerated by one decelerating axis can be consumed by another accelerating axis — real savings on high-cycle machines. The S120 communicates over PROFIBUS or PROFINET to a higher-level controller (a SIMATIC S7 PLC or a Simotion controller). It does not, by itself, run coordinated multi-axis logic — that still lives in the controller above it.

What Is Simotion?

Simotion is a dedicated motion controller. Think of it as a PLC purpose-built for motion: it runs IEC 61131-3 programs and PLCopen motion function blocks, executes cam tables, manages electronic gearing, and synchronizes multiple axes in real time — all with the deterministic cycle times that motion demands.

Simotion is not a drive. It does not power a motor. It commands drives (typically Sinamics drives connected via PROFINET or Drive-CLiQ) and coordinates what they do together.

Where Is Simotion Located in a Machine?

Simotion sits in the control tier, not the power tier. Physically, it mounts in the main control cabinet alongside — or integrated into — other control hardware. It has been available in several hardware form factors; confirm current availability with Siemens, as the product lineup evolves:

Simotion D: Integrated directly into a Sinamics S120 Control Unit. One module does both drive control and motion sequencing. Common in compact machines.
Simotion C: A standalone module designed to work with a SIMATIC rack, using the backplane for I/O while running its own motion runtime independently. Confirm current availability and supported rack types with Siemens, as this form factor's status may have changed.
Simotion P: A PC-based version running the Simotion runtime on an industrial PC. Highest computational headroom; used in machines requiring complex HMI integration or heavy mathematical processing. Confirm current availability with Siemens, as PC-based offerings in this family have evolved over time.

Typical Siemens motion architecture: Simotion commands Sinamics drives over PROFINET; drives convert power and spin motors. The S7 PLC handles broader machine sequencing above Simotion.

Sinamics vs. Simotion: Head-to-Head

Sinamics vs. Simotion at a glance — each product's primary identity, where it lives in the cabinet, and its ideal application.

Feature	Sinamics	Simotion
Primary role	Drive / power conversion	Motion sequencing / coordination
Powers the motor?	Yes	No — commands a drive to do it
Runs ladder/ST logic?	Limited parameter-level logic only	Full IEC 61131-3 runtime
Multi-axis coordination	Only with external controller	Native — cam, gearing, sync built in
Typical pairing	S7 PLC or Simotion as controller	Sinamics drives as executors
Engineering tool	Startdrive (in TIA Portal)	Scout (standalone or integrated into TIA Portal — exact integration level varies by software generation)
Application examples	Pumps, fans, conveyors, servos	Packaging machines, printing, robotics

Pro tip: If your machine has one motor doing one thing (a pump, a fan, a single conveyor), you need a Sinamics drive and a standard S7 PLC. You do not need Simotion. Simotion earns its cost when axes must follow each other with sub-millisecond coordination — a flying shear, a cross-seal on a flow wrapper, a multi-axis pick-and-place.

Can They Work Together?

Yes — and they often do. On a mid-size packaging line you might see a SIMATIC S7 PLC handling machine sequencing, a Simotion D module running the film feed and sealing axes in tight synchrony, and a handful of Sinamics G drives handling infeed and outfeed conveyors that just need basic speed control. Each layer does what it is best at.

The Simotion D form factor is the clearest example of the two families overlapping: Siemens literally merged the Simotion controller runtime into the Sinamics S120 Control Unit hardware. One box, two identities.

What Companies Make Competing Products?

Several vendors cover similar territory:

Rockwell Automation — Kinetix servo drives pair with ControlLogix/CompactLogix PLCs running the Logix motion instruction set. Similar drive-plus-controller architecture. (rockwellautomation.com)
Mitsubishi Electric — MELSERVO servo drives with MELSEC PLC or the MELSOFT Motion controller for coordinated axes. (mitsubishielectric.com)
Omron — Accurax / G5 servo drives with Sysmac NJ/NX PLCs offering built-in PLCopen motion. (omron.com)
Schneider Electric — Lexium servo drives with Modicon M262 logic/motion controllers. (se.com)
Danfoss — Strong in general-purpose VFDs (FC series); less presence in high-end coordinated motion. (danfoss.com)

No competitor maps perfectly to Simotion's architecture. The closest functional match is Rockwell's Logix motion platform or Omron's Sysmac — both embed motion coordination directly in the PLC rather than separating it into a dedicated motion controller.

Common Problems When Working With These Systems

Sinamics Fault Codes Not Clearing

Most Sinamics faults require the fault condition to be resolved first — clearing the fault code before fixing the root cause just results in immediate re-fault. Check the fault buffer in Startdrive or via the BOP-2 operator panel. Fault codes are documented in the Sinamics List Manual available on support.industry.siemens.com.

Simotion D Axis Not Enabling

A common trap: the Simotion axis object requires both the drive to be ready (Sinamics-side) and the motion enable in the Simotion program to be set. Check both layers. Missing safety signals (STO/SBC) on the Sinamics side will prevent enable at the Simotion level and may not throw an obvious alarm.

Drive-CLiQ Topology Errors After Hardware Swap

Sinamics S120 systems use Drive-CLiQ cables to auto-detect connected hardware. Swapping a Motor Module or encoder without updating the topology in Startdrive causes topology faults on startup. Always compare actual vs. configured topology after any hardware change. The exact menu path for topology comparison varies by Startdrive and TIA Portal version — consult the online help in your installed software or the Sinamics commissioning manual for your firmware generation.

Engineering Software Version Mismatches

Simotion Scout project files are version-specific. Loading an older project into a newer Scout version — or vice versa — requires a migration step. Do not skip it. Projects that include Simotion components within TIA Portal have their own version compatibility requirements. Check the project's hardware configuration target firmware against the physical hardware before commissioning, and consult the release notes for your specific software version to understand the supported hardware and firmware combinations.

When Replacement Makes More Sense Than Repair

Sinamics drive boards age. Capacitors degrade, IGBT modules fatigue from thermal cycling, and fan bearings fail. If a drive has taken a hard fault (overcurrent, ground fault, DC bus overvoltage from a motor insulation failure), internal damage may be present even after the fault clears. Similarly, Simotion D control units can fail — flash memory corruption, processor faults, or simply a unit that was in the wrong place during a lightning event. Spending weeks chasing a board-level repair on a production-critical axis rarely makes sense.

⚡ Need a tested replacement?

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Disclaimer: This guide is provided for general information only. Procedures vary by model, series, and firmware version. Industrial equipment can cause serious injury, equipment damage, or downtime if serviced incorrectly. Always consult the manufacturer's official documentation and a qualified professional before performing work, and follow your facility's lockout/tagout and safety procedures. PLC Department is an independent surplus supplier and is not affiliated with or endorsed by the manufacturers referenced. Use this information at your own discretion.