SIMOTION C240 vs D435 for Hydraulic Axis Positioning with 0–10 V Analog Feedback

Hydraulic axes for press clamping, die-cushion control, lifting/lowering, and tool change applications rarely justify the cost of an absolute or incremental encoder when the cylinder already carries a rod-mounted linear potentiometer. Most field installations expose a 0–10 V, 4–20 mA, or 0–20 mA position signal that the controller must close-loop against a proportional or servo-proportional valve command. The Siemens SIMOTION platform is one of the few motion controllers that natively accepts this topology without requiring a stand-alone position transducer interface card, and the C240 (compact, S7-300 form factor) and D435 (SINAMICS S120 form factor) are the two workhorses for this duty. This reference compares the two controllers for analog-feedback hydraulic service, walks through the analog-input and axis-object configuration, and documents the migration path from the discontinued IP252m and WF760 series.

1. Hydraulic Position Control Architecture Overview

A closed-loop hydraulic position axis contains four functional blocks: a position feedback transducer, a controller, a power-stage (proportional valve amplifier), and the hydraulic actuator. The transducer is typically one of:

• Linear potentiometer (voltage divider, 0–10 V or ±10 V)
• LVDT / LVIT (4–20 mA or ±10 V)
• Magnetostrictive or magnetoresistive non-contact position sensor (0–10 V, 4–20 mA, SSI, IO-Link)

The controller generates a velocity or flow demand that drives a proportional valve (typical ±10 V or ±20 mA command) or a servo-proportional valve (with on-board PID). The controller's task is to convert the position error into a stable, damped valve command, with the additional challenge that hydraulic systems exhibit strongly position-dependent load pressure, dead-band from valve overlap, and oil-column compliance.

For SIMOTION, the configuration is exposed through a TO (Technology Object) of type Axis > Hydraulic axis with a position setpoint interface. The position actual value is wired either to an onboard analog input (C240 has 4 onboard AI, D435 has none of its own) or to a TM15 / TM31 / SM331 expansion terminal. The valve setpoint is routed to an analog output on the same hardware or to a SINAMICS drive telegram.

2. C240 vs D435 Hardware and Application Comparison

The two controllers are functionally equivalent from the SIMOTION runtime perspective—the same SCOUT project, the same MCC diagrams, the same LADDR / ST code, the same axis TO—yet they differ substantially in their mechanical form factor, I/O density, and slot-in-SINAMICS convenience.

For a stand-alone hydraulic press where the controller is mounted in a cabinet away from the SINAMICS drive line-up, the C240 PN is the natural selection because all four analog inputs are on-board and all four analog outputs are sufficient for up to four proportional valve axes. For a press that is one of several motion axes on a SINAMICS S120 multi-axis drive (e.g., a press line with electric servo axis + hydraulic axis on the same drive bus), the D435-2 is preferable because the DRIVE-CLiQ backplane eliminates a PROFIBUS segment and synchronises the hydraulic axis to the drive clock down to 250 µs.

2.1 When to Choose C240 PN

• Stand-alone hydraulic machine with 1–4 axes and no SINAMICS S120 drive cabinet.
• Greenfield cabinet where the controller fits an S7-300 subrack alongside ET200 I/O.
• Replacement of legacy WF726 / WF760 / IP252m controllers where the existing 0–10 V wiring is to be reused.
• No DRIVE-CLiQ; the valve amplifier is a stand-alone VT-MRMA, VT-MARC, or MOOG servo valve driver.

2.2 When to Choose D435-2

• Multi-axis SINAMICS S120 line-up where the hydraulic axis is closed-loop via Active Line Module + Motor Module topology (electric + hydraulic hybrid press).
• Need for high-resolution synchronization (electronic cam) between the hydraulic axis and an electric servo axis.
• Need to scale beyond 6 axes by adding CX32-2 controller extensions (each adds another 6 axes).

3. Hardware Selection: Position Sensors and Valve Amplifiers

Although the SIMOTION controller can be configured for any analog position signal, the sensor and valve choices strongly influence the achievable axis accuracy. Typical field selections:

4. Configuring the Analog Input as a Position Actual Value

The most common configuration mistake is to declare the potentiometer as an encoder. In SIMOTION SCOUT / TIA Portal, every analog input that is used as a position actual value must be assigned to a TO_Axis's PositionActualValue interface, but the actual physical input must be configured on the AI channel of the I/O device, not on the encoder interface.

4.1 Wiring a 0–10 V Potentiometer to C240 PN Onboard AI 0

1. Route the potentiometer wiper to pin 1 of the 24-pin front connector of the C240 PN (AI0+).
2. Connect the potentiometer ends to the +24 V supply (or to the on-board 10 V reference if available) and the AG (analog ground) terminal.
3. Tie the cable shield to PE at the cabinet gland; tape the shield back at the sensor side to prevent ground loops.
4. Set the input range using the hex switch on the back of the C240, or in HW Config: 0 = voltage ±10 V, 2 = voltage 0–10 V, 3 = current 0/4–20 mA.

4.2 Setting the Analog Input in HW Config (SCOUT)

Open the C240 device in the project tree, navigate to Properties > Analog Inputs > Channel 0, and set:

• Measurement type: Voltage
• Range: 0 – 10 V
• Integration time: 60 Hz (16.67 ms) for 50 Hz line, 50 Hz for 60 Hz line (matches the line frequency rejection requirement)
• Diagnostics: enable overflow and wire-break

4.3 Declaring the AI in the Axis TO

Open the axis TO (for example Axis_HydraulicCylinder1), and under Configuration > Actual Position Value select Encoder system > Analog input. In the assignment dialog, browse to C240 PN - AI0 and confirm. The TO will then treat the 0–10 V value as the position actual. If the potentiometer is wired such that 0 V = fully retracted and 10 V = fully extended, and the cylinder stroke is 500 mm, the axis is scaled with:

with the units of mm. The scaling is configured in the TO under Mechanical System > Load Gear > Position Resolution.

4.4 When to Use a Separate TM15 / TM31 Terminal

If the C240 PN onboard AIs are already used (e.g., for 4 axes + 1 pressure transducer), or if the application requires 16-bit resolution rather than the 12-bit onboard, plug a TM15 (16 AI, 16-bit) or TM31 (basic I/O with 2 AI, 2 AO) terminal into the PROFINET line. The TM15 supports the full SIMOTION Terminal Module configuration under HW Config and exposes the channels as standard AI addresses.

5. Axis Technology Object Configuration for Hydraulic Position Control

The hydraulic-specific axis type in SIMOTION SCOUT (and TIA Portal from V15.1 onwards with the SIMOTION Option) is the TO_Axis with Axis type = Hydraulic axis. The configuration checklist:

5.1 The Position Controller Tuning Cycle

Hydraulic tuning is iterative. A safe commissioning sequence:

1. Set Kp = 1, Tn = 10 s, Tv = 0, no feedforward, no setpoint filter.
2. Jog the axis at 10 % velocity, observe the response on the SCOUT trace: aim for critically damped with 5–10 % overshoot.
3. Increase Kp by 50 % steps; once overshoot exceeds 5 %, reduce by 30 % and record that as Kp_max.
4. Set working Kp = 0.5 × Kp_max.
5. Reduce Tn from 10 s down until the trace shows oscillation; double the time as working Tn.
6. Add a setpoint filter (PT2) of 30 ms to suppress jerk into the valve.
7. Engage the controller in fully closed-loop mode and verify position tolerance.

6. PLCopen vs System Motion Commands

SIMOTION exposes two command sets to the application programmer:

The two can be mixed freely in the same program. A typical pattern is to use MC_MoveRelative for the main motion command and then call _stop for a fast stop, or to use a PLCopen block to start the motion and a system command to dynamically override velocity mid-travel.

6.1 Example: PLCopen move in ST (LAD/FBD equivalent)

// Jog hydraulic axis to position 250.0 mm at 50 mm/s
IF bStartMotion AND Axis_HydCyl1.StatusWord.X7 THEN  // X7 = Standstill
  MC_MoveRelative(
    Axis := Axis_HydCyl1,
    Execute := TRUE,
    Distance := 250.0,
    Velocity := 50.0,
    Acceleration := 100.0,
    Deceleration := 100.0,
    Done => bMoveDone,
    Busy => bMoveBusy,
    CommandAborted => bMoveAborted,
    Error => bMoveError,
    ErrorID => wMoveErrorID);
END_IF;

6.2 Example: System _move in MCC diagram

The MCC equivalent is a single function-block call: _move(axis := Axis_HydCyl1, position := 250.0, velocity := 50.0, acceleration := 100.0). The MCC has the advantage of graphical display of the execution, blend, and abort transitions, and is the preferred authoring language in most SIMOTION application examples.

7. Migrating Logic and Programs Between C240 and D435

SIMOTION programs and libraries are independent of the controller hardware—the same .scc (SCOUT project) can be compiled and downloaded onto any C, D, or P platform provided the required Technology Packages are loaded. The migration checks before download are:

1. Verify the Technology Packages license on the target controller covers the axis types used. The CAM and PATH packages, if used, must be present on the target.
2. Verify I/O mapping. The C240's onboard AI/AO addresses (e.g., IW 100–107, QW 100–107) must be re-mapped to the TM15 / SINAMICS terminals used on the D435.
3. Re-validate PROFIBUS / PROFINET device names and IP addresses. The D435-2 PN uses the SIMOTION part of the D435-2 image; the PROFINET device name must match the new commissioning step.
4. Re-run axis commissioning (Tuning). The hydraulic column dynamics are independent of the controller, but the controller cycle time changes from 2 ms (C240) to 1 ms (D435), and a lower cycle time may demand a different Kp.
5. Verify encoder / analog input scaling. The C240's onboard 12-bit AI is replaced with TM15 16-bit on the D435; the raw LSB count changes, but the SIMOTION TO scaling is in engineering units, so the scaling itself is unchanged.

A practical rule is: the SIMOTION runtime is portable, but the hardware configuration is not. Keep the I/O re-mapping in a separate project or as a documentation deliverable when migrating between C and D platforms.

8. Successors to IP252m and WF760

The legacy SIMATIC positioning modules and the older WF series have been progressively replaced. The mapping for typical analog-feedback hydraulic retrofit projects is:

For a WF726 retrofit, the cabinet footprint and 0–10 V wiring can be reused almost completely. The key replacement is the controller; the existing potentiometer and proportional valve amplifier are typically retained. For an IP252m replacement, the SIMATIC S7-300 subrack can sometimes be reused, with the IP252m swapped for a C240 PN in the same slot pattern.

9. Alternative Platforms for Hydraulic Position Control with Analog Feedback

SIMOTION is the Siemens preferred path, but several alternatives are valid when the application allows a different ecosystem.

9.1 Allen-Bradley / Rockwell 1756-HYD02

The 1756-HYD02 is a ControlLogix Hydraulic Servo Module that closes position loop from a linear displacement transducer (LDT) input and drives a proportional valve. The module has a single LDT (start/stop pulse) input, an SSI input, a 4–20 mA feedback input option, and a ±10 V analog output to the valve. The 1756-HYD02 is configured with RSLogix 5000 / Studio 5000 add-on profile and supports up to four position-loop axes with on-module auto-tuning. The module's 1756-HYD02 user manual documents the LDT scaling (1 µs / 102.4 µs = 1 mm typical for a Balluff LDT), the valve command limits, and the on-board tuning procedure. The 1756-HYD02 is a strong choice when the cabinet is already a ControlLogix system and the hydraulic axis is one of many Logix axes.

9.2 Delta RMC Motion Controllers

Delta RMC75, RMC150, and RMC200 motion controllers accept 0–10 V, ±10 V, and 4–20 mA analog position feedback and can close-loop directly against a proportional valve. They support IEC 61131-3 languages (ST, FBD, LD) and EtherNet/IP, PROFINET, and Modbus TCP industrial network attachment. They are widely used in hydraulic press, injection molding, and die-cast applications. The RMC's Tuning dialog includes a hydraulic-specific auto-tuning pass that sets Kp, Kd, and feedforward based on step response data.

9.3 Bosch Rexroth VT-HNC and IndraMotion

Bosch Rexroth produces the VT-HNC hydraulic axis controller (digital, 0–10 V feedback) and IndraMotion MLC for higher-end systems with electric + hydraulic hybrid axes. The VT-HNC is a direct successor to the VT-MRMA and VT-MARC amplifier-generation controllers, and includes an integrated fieldbus (EtherNet/IP, PROFINET, or CANopen) interface.

9.4 AutomationDirect / Parker / Moog stand-alone

For one-axis or two-axis systems without a multi-axis controller, stand-alone controllers such as the Parker Compax3, Moog MSD, or AutomationDirect ProductivityOpen with a Click PLC and a stand-alone valve amplifier can be lower-cost. The trade-off is that synchronization to other axes is more limited.

10. Commissioning, Verification, and Safety

After the SIMOTION project is compiled and downloaded, the commissioning sequence is:

1. Set the axis to simulation mode and run a dry cycle: confirm that the analog input reads correctly, the scaling maps 0–10 V to 0–500 mm, and the valve output responds to a setpoint change.
2. Switch to test mode with the proportional valve enabled and no load. Jog the axis at 5 % velocity and watch the trace for oscillation.
3. Increase load, increase velocity, and re-tune per the §5.1 procedure.
4. Engage follow-up mode: verify that the controller output goes to zero in standstill (the valve amplifier is at the null point), and the position error is within tolerance.
5. Test the safe stop path: trigger an external ESTOP, confirm the axis decelerates under the configured stop ramp, and that the proportional valve is driven to the failsafe (e.g., 0 V or to the spring-offset voltage).
6. Verify the software limit switches (positive and negative) by jogging into them; the controller must stop the axis without overshoot.
7. Verify the hardware limit switches (if fitted) and the E-Stop chain.

11. Troubleshooting Matrix

12. Frequently Asked Questions