Siemens G120 vs S120: Key Differences and How to Choose

A comprehensive comparison for engineers and procurement teams evaluating Siemens SINAMICS drives for industrial applications.

1. Introduction

Both the Siemens SINAMICS G120 and SINAMICS S120 are equipped with a PID process controller — yet the two drives differ significantly in functional design, application scope, and performance characteristics. Choosing the wrong platform can result in over-engineering or under-performance, both of which carry real cost consequences.

This article compares the G120 and S120 across four core dimensions: core functions and architecture, parameter configuration, application scenarios, and performance optimization. Whether you are an OEM engineer, system integrator, or procurement specialist, this guide will help you identify the right Siemens drive for your project.

2. Product Overview

2.1 Siemens SINAMICS G120

The SINAMICS G120 is a modular, general-purpose AC drive for standard industrial applications. It pairs a Control Unit (CU) with a Power Module (PM) that can be independently selected based on power and enclosure requirements.

• Power range: 0.37 kW – 250 kW (3AC 380V standard)
• Control modes: V/f, open-loop vector, closed-loop vector
• Built-in PID controller for level, temperature, pressure, and speed
• Communication: PROFIBUS, PROFINET, USS, Modbus RTU
• Safety: STO (Safe Torque Off) as standard
• Enclosure: IP20 standard; IP55 via push-through mounting

By default, the G120 output is bound to the speed setpoint (P1070). Introducing third-party physical quantities such as torque or position requires setting P1501 = 1 to release this binding. Analog step response typically exceeds 10 seconds, making the G120 best suited for stable steady-state control rather than fast transient applications.

2.2 Siemens SINAMICS S120

The SINAMICS S120 is a high-performance, modular drive system designed for demanding motion control and process applications. Its shared DC bus architecture allows multiple Motor Modules to share a single Line Module, enabling energy exchange between axes.

• Power range: 0.12 kW – several MW
• Control modes: Vector, Servo, V/f
• Advanced PID with auto-tuning, dual scalable setpoints, and f(x) function blocks
• Encoder feedback required for servo mode; flexible derivative channel for complex PID
• Safety: STO, SS1, SLS, SDI, SOS, SSM — up to SIL 2 / PLe (Cat 4)
• Communication: PROFIBUS, PROFINET, EtherNet/IP, DRIVE-CLiQ

The S120's derivative channel can freely connect to control deviation or actual measured values. These capabilities make it the preferred choice wherever the G120's architecture reaches its limits.

3. Specification Comparison

4. Key Differences Explained

4.1 Core Architecture and PID Capability

The G120 supports simple closed-loop PID control for liquid level, temperature, and pressure — ideal for fans, pumps, and similar loads where dynamic response requirements are modest. Its single-loop PID is straightforward to configure and well-proven in utility and HVAC applications.

The S120 provides a substantially richer control environment: liquid level, temperature, floating roll position, tension, and multi-variable coordinated control are all natively supported. It also features dual scalable setpoints, a flexible electric positioner, and a ramp function generator.

4.2 Dynamic Response

The G120's analog step response typically exceeds 10 seconds — well-suited for steady-state control but limiting for fast transient applications. The S120 delivers current control cycle times as short as 62.5 μs, essential for CNC, robotics, printing, and winding applications.

4.3 Safety Functions

Both drives support STO (Safe Torque Off). The S120 additionally provides a safety library certified to IEC 62061 (SIL 2) and ISO 13849 (PLe / Cat 4):

• SS1 – Safe Stop 1
• SLS – Safely Limited Speed
• SDI – Safe Direction Indication
• SOS – Safe Operating Stop
• SSM – Safe Speed Monitor

4.4 System Integration and Scalability

The G120 integrates via PROFIBUS or PROFINET, with each unit configured independently. The S120 integrates deeply with TIA Portal and SINUMERIK via DRIVE-CLiQ — enabling automatic parameter identification and centralized diagnostics. In a 6-axis packaging line case, DRIVE-CLiQ integration reduced commissioning time by approximately 40%.

5. PID Parameter Configuration

5.1 G120 PID Setup

Enable PID by setting P2200 = 1. Setpoint source: P2253 = r2050.1 (PROFINET) or r755.0 (AI0). Feedback: P2264 = r755.0. For bar pressure control, set P595 = 3 and P596 = 10 (100% = 10 bar).

5.2 S120 PID Setup

S120 PID requires adjusting P, I, and D parameters according to the controlled object's dynamic characteristics. The logic inversion parameter P2306 must be configured carefully. The S120's auto-tuning function automatically identifies motor model parameters and optimizes PI settings, significantly reducing commissioning effort.

6. Typical Application Examples

6.1 G120 Application Scenarios

Fan speed closed-loop control: G120 pairs with an anemometer for constant wind speed. PID time constants typically range from tens of seconds — ideal for the G120's steady-state strengths.

Constant-pressure water supply: Pressure sensor + pump + built-in PID maintain stable water pressure for moderate dynamic response requirements.

Constant-temperature control: Temperature sensors with PID loop enable precise regulation of heating or cooling systems.

Case example — Water treatment plant: G120 with PROFINET controlled 12 pump motors via SCADA. Built-in PID eliminated a separate process controller, reducing panel cost by approximately 20%.

6.2 S120 Application Scenarios

Floating roll position control: S120 responds rapidly to external disturbances for stable, reliable positioning in continuous process lines.

Tension control: Precise motor output torque adjustment achieves fine control over tension variations in winding and printing.

Multi-variable coordinated control: Simultaneous liquid level and flow regulation, with dual scalable setpoints for complex control requirements.

Case example — High-speed packaging line: S120 with 6 synchronized axes replaced a hydraulic servo system. Throughput increased 30%, energy consumption fell 15%, and hydraulic maintenance costs were eliminated.

7. How to Choose: Decision Guide

Choose G120 if:

• Your load is a pump, fan, conveyor, compressor, mixer, or centrifuge
• Speed accuracy under V/f or open-loop vector (≥ ±0.5%) is acceptable
• You need a cost-effective standalone drive with simple PID wiring
• Compact IP55 push-through installation is required
• Budget is a primary project constraint

Choose S120 if:

• Your machine requires servo-level precision or fast torque response (< 10 ms)
• You need to synchronize 2 or more motor axes
• The application involves CNC, robotics, printing, winding, or tension control
• Advanced functional safety (SS1, SLS, SDI — SIL 2) must be certified
• Energy recovery between axes is important for operating cost

8. Performance Optimization

G120: The adaptive function (firmware V4.7.13+) adjusts PID time constants automatically. Fine-tune mode (P2251 = 1) enables precision control near setpoint. The f(x) function supports nonlinear characteristics such as propeller blade curves without external devices.

S120: Auto-identification eliminates manual PI tuning iterations. P/I/D adjustment targets oscillation and steady-state deviation. Multi-zone and cascade strategies address process dynamics beyond single-loop capability.

9. Cost and Total Cost of Ownership 

A G120 for a 15 kW motor typically costs 30–50% of an equivalent S120 system. However, TCO should also account for:

• Panel space and wiring: S120 shared DC bus reduces cabling in multi-axis systems
• Energy savings: S120 regenerative modules can reduce energy costs by 10–25% in frequent-braking applications
• Maintenance: Both platforms support predictive diagnostics via PROFINET
• Engineering time: S120 with TIA Portal and DRIVE-CLiQ can reduce commissioning time by up to 40% in complex projects

For single-motor applications, G120 almost always wins on TCO. For 3+ axis systems, S120 frequently becomes cost-competitive when energy recovery and reduced wiring labor are factored in.

10. Common Model References

Note: Always verify article numbers using the Siemens SIZER configurator or contact your authorized distributor, as options affect the order code.

Conclusion

Both the Siemens SINAMICS G120 and S120 are outstanding products within their respective domains:

• G120 = the right tool for standard industrial drive applications (pumps, fans, conveyors, compressors)
• S120 = the right tool for motion control, high-precision multi-axis, and advanced process control

If you are uncertain which platform fits your application, contact our engineering team with your motor specifications, load type, and control requirements. We supply genuine Siemens SINAMICS G120 and S120 drives with full documentation, warranty, and technical support.