Choosing Between Profinet and Drive-CLiQ Encoders for S7-1500T

Application Context and Architecture

A press automation cell built on the SIMATIC/SINAMICS portfolio typically integrates an S7-1500T controller (technology-grade, supports camming, gearing, and kinematic transformations), one or more ET200SP distributed I/O stations on PROFINET, and a Sinamics S120 multi-axis drive line-up with a CU320-2 PN control unit. In the configuration covered here, the S7-1500T orchestrates the press kinematics and a separate external encoder is used as a master axis source for one or more TO_SynchronousAxis technology objects. The drive axes each have their own motor-mounted encoder; the external encoder is a process reference (ram position, slide position, transfer axis) that is not part of the drive's torque or velocity loop.

Two catalog-numbered encoders in the Siemens 6FX2001-5 series compete for this role:

• 6FX2001-5FN25 — PROFINET IO encoder, fitted directly to the PROFINET segment, published as a PROFINET IO device.
• 6FX2001-5FD25-1AA0 — DRIVE-CLiQ encoder, fitted to the CU320-2 control unit, exposed to PROFINET as a PROFIdrive telegram on the CU320-2.

Both deliver absolute singleturn/multiturn position data; the architectural and engineering-tool differences dominate the selection rather than the headline resolution. The decision is determined by which controller owns the position value, which PROFIdrive telegram carries it, and which engineering tool can configure the corresponding technology object. Reference: SIMATIC S7-1500T Motion Control Function Manual.

Encoder Family Identification: 6FX2001-5x Catalog

The 6FX2001-5 series belongs to the Siemens built-on absolute encoder family intended for SIMOTION, SINAMICS, and SIMATIC motion applications. The catalog-number convention decodes as follows:

Mounting interfaces, shaft diameters, and electrical connector assignments are typically the same form factor, so the mechanical installation is interchangeable; verify against the 6FX2001 data sheet for the press-side shaft, flange, and coupling.

Signal Path Comparison: PROFINET vs DRIVE-CLiQ

The two encoders take fundamentally different routes from the shaft to the S7-1500T motion control firmware.

PROFINET IRT path (6FX2001-5FN25)

The encoder is a PROFINET IO device. It exposes a Position Encoder Submodule (PES) that the S7-1500T inserts into its device view. The S7-1500T reads the position directly from the encoder's IRT slot in each bus cycle. No drive-side controller is in the path; the encoder is sampled by the PROFINET I/O at the configured IRT send clock (typically 1 ms, optionally 0.5 ms or 0.25 ms on 1500T).

DRIVE-CLiQ path (6FX2001-5FD25-1AA0)

The encoder speaks DRIVE-CLiQ to the CU320-2. The CU320-2 samples the position, places it into a PROFIdrive slot 2/3 telegram (typically 81 or 83, or 106 for a second encoder of a drive object), and the S7-1500T reads it from the CU320-2's PROFINET interface. The CU320-2 is therefore in the timing path: the position the 1500T sees is delayed by one PROFIdrive sampling plus one PROFINET cycle.

PROFIdrive Telegrams for External Encoders

When a DRIVE-CLiQ encoder must be exposed to PROFINET for an external consumer, the CU320-2 must publish a position-encoder submodule and a PROFIdrive telegram in its device view. The relevant telegrams are defined by the PROFIdrive profile and the Siemens PROFIdrive conformance class 4 implementation. Reference: SINAMICS S120 Communication Function Manual.

For a 1500T external encoder on a CU320-2, the typical configuration is:

1. Insert the encoder as a second encoder on an existing drive object (Servo or Vector) in the CU320-2 device view.
2. Assign PROFIdrive telegram 106 to that drive object, which carries two 32-bit actual position values.
3. In the 1500T, configure a TO_ExternalEncoder and interconnect it to telegram 106's second encoder word set (G2_XIST1 / G2_XIST2).

If the encoder is to be a true field-level external encoder (not attached to a drive object), the encoder must be configured in the CU320-2 as an encoder with free assignment and the corresponding telegram (81 or 83) is published as a slot without a drive object. This is the configuration path that Startdrive historically blocks.

Telegram 81/83 detailed word layout

G1_XIST1 is the master position value used by the 1500T for the cam, gear, or cam-track coupling. G1_XIST2 is typically the same value with a finer resolution (sub-encoder bit) or a marker-based value for homed applications; the 1500T TO_ExternalEncoder can be configured to use either.

S7-1500T Technology Object Configuration

The 1500T firmware treats the external encoder as one of two distinct object classes, depending on which path it arrived on.

For a press master axis, the canonical TO chain is:

TO_ExternalEncoder  —master position-->  TO_SynchronousAxis  —cam coupling-->  TO_Cam / TO_CamTrack
                                            |
                                            +-- gear coupling
                                            |
                                            v
                                       (slave drive axis)

The interconnection is configured in TIA Portal under Technology objects → Synchronous axis → Interconnection → Master value source. The 1500T evaluates the master position in every MC-Servo cycle (typically 1 ms) and computes the slave setpoint from the active cam or gear coupling.

Key TO_ExternalEncoder parameters

Startdrive Limitation and the STARTER Workaround

At the time of the original application, Startdrive (the SINAMICS commissioning plug-in inside TIA Portal) does not support configuring an external encoder with telegram 81/83 as a stand-alone submodule on the CU320-2 PN. Startdrive's drive-object wizard is optimised for drive axes, not for free-encoder assignments, so the encoder cannot be added to the project with the right telegram subtype from the TIA device view alone.

Two workarounds are available:

Workaround A: STARTER + GSDML hybrid configuration

1. Import the CU320-2 PN GSDML into TIA Portal as a third-party PROFINET device. Do not use the Startdrive device proxy for the CU320-2 PN in this mode.
2. Open STARTER (or Startdrive offline) with a separate project to load the encoder submodule and assign telegram 81 or 83 to the encoder.
3. Save the SINAMICS project to the CF card or download to the online drive and restart the CU.
4. Re-import the configuration into TIA Portal and connect the 1500T TO_ExternalEncoder to the appropriate telegram slot of the GSDML device.

Workaround B: Second-encoder on a drive object with telegram 106

1. Assign the DRIVE-CLiQ encoder as a second encoder on any servo or vector drive object in the CU320-2 (typically a real axis in the same drive line-up).
2. Configure PROFIdrive telegram 106 on that drive object, which carries two encoder channels.
3. In the 1500T, the second encoder channel of telegram 106 is available as a PROFIdrive actual value. Connect it to a TO_ExternalEncoder via the PROFIdrive encoder configuration source.

For a press application that needs the encoder to remain available to the controller regardless of any single drive's state, the PROFINET encoder is the simpler architecture: it is configured entirely in TIA Portal, no STARTER detour, no GSDML gymnastics, no dependency on a drive's online state. Reference: SINAMICS STARTER Commissioning Tool.

Latency and Synchronization Accuracy

Press dynamics drive the latency budget. A typical mechanical press line operates with the ram following a cam profile at velocities up to several metres per second. The position lag between the master encoder and the slave drive is:

L = v × t_total

where v is the ram velocity (mm/s) and t_total is the total sample-to-actuation delay (s).

For a press running at 1 m/s with a 2 ms total delay, the slave is 2 mm behind the master; for a 5 m/s high-speed press with a 4 ms total delay, the lag is 20 mm. These numbers sit inside the cam tolerance band of typical press lines but become the limiting factor for high-precision indexing at bottom dead centre.

Latency budget by path

The two paths are within one PROFINET cycle of each other. With an IRT send clock of 1 ms, the difference is in the 0.25–0.5 ms range. For a press running 0.5 m/s the difference is sub-millimetre; for a press running 5 m/s it becomes 1–2 mm and is observable in the cam trace.

IRT cycle-time selection

The 1500T supports IRT send clocks of 250 μs, 500 μs, 1 ms, 2 ms, and 4 ms. A faster send clock tightens the latency but increases the bus load and CPU load on the 1500T. For a press with 1 ms MC-Servo, the practical minimum IRT send clock is 1 ms; lower values are over-engineered unless the cam trace shows jitter from PROFINET phase variation.

Press-Specific Selection Criteria

Beyond latency and engineering tooling, a press line imposes constraints that should be checked against the encoder data sheet and the cell layout.

• Mechanical isolation: A press master encoder is mounted on a separate mechanical reference (frame, transfer axis, slide). DRIVE-CLiQ has a maximum cable length of approximately 100 m (varies by cable type), and PROFINET copper is typically limited to 100 m. Both are sufficient for the press cell; PROFINET copper is the more flexible option if the encoder is more than 30 m from the cabinet. PROFINET fibre (via SCALANCE) extends this further for very large press lines.
• Vibration and shock: A press generates shock loads on every stroke. Verify the encoder's vibration and shock rating against the press-side mounting point. Both candidates in the 6FX2001 family carry industrial vibration ratings; however, the connector retention under shock favours the M12 PROFINET connector with vibration-rated overmoulds over the DRIVE-CLiQ RJ45-style connector for press-side mounting.
• Oil and coolant exposure: A press in a lubricated environment requires an IP-rated encoder. The 6FX2001 family offers IP67 variants; check the exact suffix on the ordered part number.
• Resolution vs mechanical lead: Press applications rarely need 25-bit singleturn resolution. A 20–22 bit singleturn is more than adequate for stroke lengths up to 1–2 m. Resolution rarely decides the question.
• Safety integration: If the encoder feeds a safety-related path (e.g. safe cam monitoring, safe limited position, SLS on a press axis), the chosen encoder must support the safety function set. PROFINET encoders with PROFIsafe profile and DRIVE-CLiQ encoders integrated into SINAMICS Safety Integrated Extended Functions are both available in the 6FX2001 family; verify the exact catalog number for the safety variant.
• Hot-swap and replacement: A PROFINET encoder is replaced by swapping the IO device; a DRIVE-CLiQ encoder is replaced through the SINAMICS topology editor, which has to rediscover the encoder on the DRIVE-CLiQ ring. For a press line where the operator may need to replace the encoder after a fault, the PROFINET path is the more user-friendly workflow.
• Cost and inventory: A PROFINET encoder is a generic PROFINET IO device and can be sourced from a wider vendor pool; a DRIVE-CLiQ encoder is typically a Siemens-only part because of the proprietary DRIVE-CLiQ interface. For a multi-press plant with a single spare-parts pool, the PROFINET option is usually easier to stock.

Commissioning Procedure

The procedure differs by encoder choice.

PROFINET encoder (6FX2001-5FN25) — TIA Portal only

1. Add the encoder's GSDML to TIA Portal and insert the device into the PROFINET topology on the same IRT subnet as the 1500T.
2. Assign the encoder a PROFINET name and IP address via the topology editor or PRONETA.
3. Set the IRT send clock on the PROFINET subnet to 1 ms (or 0.5 ms / 0.25 ms for tighter determinism).
4. Insert a TO_ExternalEncoder in the technology-object tree and assign the encoder's PROFINET submodule as the position source.
5. Set the encoder's mechanical parameters: singleturn bits, multiturn bits, units per revolution, modulo value, scaling factor, and direction reversal.
6. Insert a TO_SynchronousAxis for the slave drive; interconnect the TO_ExternalEncoder as the master value source.
7. Configure the cam (TO_Cam) or cam track (TO_CamTrack) on the synchronous axis with the press-specific profile.
8. Download the project to the 1500T and use the Axis control panel in TIA Portal to verify the encoder value tracks the shaft rotation with the expected sign and scaling.

DRIVE-CLiQ encoder (6FX2001-5FD25-1AA0) — hybrid tooling

1. In the SINAMICS project (Starter or Startdrive), add the DRIVE-CLiQ encoder to the CU320-2 topology. The encoder is auto-detected on the DRIVE-CLiQ ring at the next topology download.
2. Configure telegram 81 or 83 on the encoder submodule (Starter path) or assign the encoder as a second encoder on a drive object with telegram 106 (Startdrive path).
3. Configure the drive object that owns the encoder (motor identification, encoder scaling, direction reversal, mechanical parameters).
4. Save the SINAMICS project to the CF card and perform a POWER ON / CU restart.
5. In TIA Portal, import the CU320-2 as a GSDML device and connect the 1500T TO_ExternalEncoder to the PROFIdrive telegram slot.
6. Continue with steps 5–8 of the PROFINET procedure.

Diagnostics and Verification

The 1500T exposes a rich set of diagnostic blocks for the external encoder. Use them in the commissioning phase to verify the signal is alive and correctly scaled.

Verification checklist

• Sign check: Rotate the encoder shaft by hand in the positive direction. The TO_ExternalEncoder actual value must increase. Reverse wiring inverts the sign; configure the InvertDirection parameter on the TO.
• Scaling check: Rotate the shaft by exactly one mechanical revolution. The actual value must change by the configured resolution. Mismatches indicate wrong bit-count or wrong unit configuration.
• Multiturn check: Power the system off, rotate the shaft by hand by more than one revolution, power on again. The actual value must reflect the new absolute position with the correct multiturn count. A wrong multiturn count indicates wrong configuration of the multiturn bit count on the TO.
• IRT phase check: The PROFINET diagnostics must show the encoder in RT_CLASS_IRT mode and the Synchronization indicator on the encoder's PROFINET diagnostics must be Synchronized.
• Cam trace: With the slave drive in Follow-up mode, trace the master encoder value and the slave actual position on the cam trace. The relationship must follow the configured cam profile within the calculated lag.
• PROFIdrive status word check: Read the ZSW2 of telegram 83 in the 1500T and verify that bit 0 (function 1 active) is set, bit 1 (function 2 active) reflects the configured state, and the warning/error bits are clear.

Selection Decision Matrix

Use the matrix below as a structured decision aid for a press application.

For the press application in the original question, where the external encoder is the master for a synchronous axis and the drive has its own motor feedback, the PROFINET encoder is the recommended selection. The DRIVE-CLiQ encoder is the right answer only when the same encoder is also required by a drive object for the torque loop or for a Safety Integrated function that needs the DRIVE-CLiQ safety path.

Frequently Asked Questions