Resolving STARTER Control Panel Drop When Switching Tabs

Problem Statement

When commissioning a SINAMICS drive (G110, G120, G120C, G120D, G120P, G130, G150, S110, S120, S150, or DCM) with the STARTER commissioning tool, the Control Panel ("Control_panel") releases control of the drive the moment the operator switches to another work area, inspector, or external program such as an oscilloscope capture tool. The motor either ramps down on a quick stop, coasts to a stop, or remains at the last setpoint depending on the OFF2 / OFF3 configuration of the control word. The result is that any data-logging activity that requires you to navigate away from the Control Panel tab to a scope application, an analog trace view, or even STARTER's own Trace window terminates the active test sequence.

This is not a bug; it is an intentional safety behaviour: STARTER holds a software-level ownership token on the drive (also known as a "control request" or "master control") that is revoked on focus loss, tab deactivation, or program context switch. The mechanism is documented in the SINAMICS function manuals and is the same watchdog that prevents a forgotten Control Panel from leaving a multi-megawatt drive running unattended after a commissioning engineer has walked offsite.

The objective of this document is to provide six field-proven workarounds that allow simultaneous drive control and high-speed data logging without a second PC, covering the standard PROFIdrive stack on PROFINET and PROFIBUS, the SINAMICS Trace function, the S7-1500/S7-1200 control path, the SINAMICS Web Server, and TIA Portal's successor tool Startdrive.

Affected Products and Firmware

Refer to the SINAMICS G120 operating instructions and the SINAMICS S120 Commissioning Manual for the precise firmware maps on the CU variants used in your plant.

Root Cause: Control Panel Watchdog and Master Control

When you click "Assume Control" in STARTER's Control Panel, the tool sends a sequence of PROFIdrive control-word bits to the drive that effectively take ownership of the closed-loop speed/torque/position controller from the upstream PLC:

1. Bit 10 of the control word (STW1) — Control by PLC — is cleared to 0 by STARTER.
2. Bit 11 and Bit 12 (direction of rotation) are set by the operator in the Control Panel.
3. Bit 0 / Bit 1 / Bit 2 / Bit 3 (ON/OFF1, OFF2, OFF3, Enable Operation) are set/cleared by the Control Panel slider.
4. The drive's application class (Standard Drive, Positioning, or S120 dynamic) interprets this bit pattern and the supplementary setpoint channel routes the Control Panel's speed or torque command to the closed-loop controller.

The watchdog that releases control is a client-side timer inside STARTER, not on the drive. STARTER expects a periodic user-input event (mouse, keypress, or explicit "Assume Control" re-confirmation) on the active work area. The moment the Windows messaging loop receives a WM_KILLFOCUS event (tab switch, dialog open, external application focus), STARTER fires its master-control release and reasserts the original PLC ownership by setting Bit 10 to 1 and clearing Bits 0–3.

The drive's response to this transition is governed by:

If the ramp-down in p1121 is short (default 10 s for the basic ramp-function generator on G120), the motor decelerates in a fraction of a second when OFF1 is withdrawn, which gives the appearance of a "hard stop". Configure p1121 to match the connected load's inertia if this is unacceptable during testing.

Workaround 1: Use the Integrated STARTER Trace with Control Panel

The Trace function in STARTER is hosted in the same window tree as the Control Panel and therefore does not steal Windows focus. The drive's own servo-cycle trace (sampling 1 ms, 250 µs, or 125 µs depending on the SINAMICS clock) is captured to the drive's non-volatile RAM and downloaded to STARTER at the end of the run. This is the cleanest single-PC solution.

Step-by-step

1. Open the project, go online, and double-click Drive > Commissioning > Control Panel.
2. Click "Assume Control" and confirm the safety prompts. Verify that r899.0 = "Commissioning mode active" and the speed setpoint in the Control Panel is at 0 RPM.
3. Switch (do NOT close) to the Trace configuration tab. The Control Panel ownership is preserved as long as the Trace tab belongs to the same STARTER instance.
4. Click "New Trace", add the following signals from the parameter list (right-click > Insert signal):
   • r63 — Actual speed smoothed (RPM)
   • r80 — Torque actual value smoothed (Nm)
   • r52 — Control word, ZSW (status word) - useful for capturing OFF1 transitions
   • r2199 — Status word, drive status (bit 2/3/6 for operation, fault, switch-on inhibit)
   • r360 — DC link voltage
   • r1651 — Output current (current vector, RMS)
5. Configure the trigger — a typical setup is a positive edge on r2199.8 (speed setpoint reached) with a 200 ms pre-trigger and 1 s post-trigger window.
6. Set the sampling period: 1 ms is the default for SERVO; 4 ms for VECTOR. Use the finer period only if the drive-clock is set in p0115 to match the servo cycle (p0115[0] = 250 µs on S120 with a high-performance Line Module).
7. Click "Arm Trace", return to the Control Panel tab (the same STARTER instance), and move the motor using the Control Panel sliders.
8. Stop the Trace after the desired event and use "Export to CSV" for offline analysis in MATLAB, Excel, or DIAdem.

Workaround 2: Fixed Setpoint (Festwert) Operation

For a simple constant-velocity test where the engineer only needs the motor to spin at a fixed RPM while the data is captured on a different tool, the Fixed Setpoint (Festwert, FSW) function in the SINAMICS setpoint channel removes STARTER from the critical path entirely. The drive runs on a value stored in p1001, p1002, p1003, or p1004, with p1020 selecting which fixed setpoint is active.

Commissioning procedure

1. Set p1100.0 = 1 to enable the fixed setpoint mode (this BICO connects the setpoint source to p1001–p1004 instead of the analogue input or PROFIdrive master).
2. Set p1016 = r0722.0 and p1017 = r0722.1 to use the CU's on-board digital inputs as the selection bits (or connect to a binary-coded selection from the PLC).
3. Enter a safe test value in p1001 (start at 10 % of rated speed).
4. Issue ON/OFF1 from the PLC or hardwired terminal. The drive will ramp to p1001 with p1120/p1121 ramp times.
5. Capture data with the oscilloscope or a separate PC. Because the drive's setpoint is now sourced from the firmware, not from STARTER, you can quit STARTER entirely and the motor will continue to run until OFF1 is withdrawn.
6. To stop, remove the DI selection (set p1020 = 0) or withdraw OFF1 — the drive will ramp down via p1121.

Workaround 3: Alternative Access Point Routing

Siemens has documented a procedure that allows STARTER to maintain a control-panel session through a second access point — for example, using PROFINET for the control connection and USB or RS-232 for the trace. This is described in the FAQ "Addressing the inverter using STARTER via the alternative access point" (ID 24296240 on the Siemens Industry Online Support portal). The technique is also sometimes called "two-channel commissioning".

Topology

Connect the drive to the engineering PC on two separate networks:

• Channel 1 (control): the CU250S-2 PN or CU320-2 PN PROFINET port, configured in TIA Portal / STARTER as the project device.
• Channel 2 (data): a separate PROFINET or PROFIBUS segment, the Ethernet service port on the Control Unit, or a USB-to-RS-232 cable on the CU240E-2 (X-123 socket) used solely for the trace download.

Because STARTER's Control Panel ownership is bound to a specific S7 routing relationship, opening the second access point as a passive listener does NOT revoke the first channel's master control. The trace buffer can be polled continuously from the second channel without disturbing the active Control Panel session.

Step-by-step

1. Install the second interface (e.g., a CP 1616 PCIe card or a standard USB-to-RS-232 cable) and add it under Set PG/PC interface in the Windows control panel.
2. In STARTER, go to Project > Accessible nodes and select the new interface. The drive appears as a separate node with its IP/SSW address.
3. Go online with the original interface for the Control Panel; the second interface is only used by the Trace function's "Download to PG" command.
4. Run the test sequence. If the Control Panel does drop (e.g., due to a Windows graphics driver glitch), you can re-establish the connection through the second interface without interrupting the trace buffer.

Workaround 4: Switch to TIA Portal with Startdrive

The successor product to STARTER, embedded in TIA Portal, is SINAMICS Startdrive. Startdrive's Control Panel has the same focus-loss behaviour (the master-control release is part of the SINAMICS firmware, not the tool), but the trace tool inside Startdrive is more flexible:

• Long-term trace is supported up to the full RAM of the Control Unit plus a ring buffer on the PG.
• The "Control Panel" and "Trace" can be docked as split-screen windows, so the operator only ever moves the mouse inside the same TIA Portal window — eliminating the Windows focus-loss event for some configurations.
• TIA Portal V18 / V19 integrates the trace directly with the S7-1500S7-Trace, which is CPU-side and not subject to the SINAMICS firmware limitation.

Procedure

1. Convert the existing STARTER project to TIA Portal via Project > Migrate STARTER project in Startdrive.
2. Open the Control Panel and assume control.
3. Right-click on the docked Trace icon and select New trace. Use the parameter tree to drag in the same r-parameters as Workaround 1.
4. Choose Trigger on signal, point it at r2199.2 (Operation enabled), and arm the trace.
5. Switch to another TIA Portal window (the trace, a watch table, the PLC code, or the inspector) without leaving TIA Portal. Because both views are children of the same MDI frame, the Control Panel retains focus until you press Alt-Tab to a non-TIA application.

For sites still on TIA V15.1, note that Startdrive V15.1 does not support the same long-term trace options as V18. Update at least to V16 for a stable logging session; refer to the Startdrive V18 release notes for compatibility.

Workaround 5: PLC-Based Closed-Loop with Supervisory Trace

The most production-friendly solution is to make the PLC the primary controller and use STARTER/Startdrive only for the high-speed capture. With this approach, the Control Panel is not involved at all — the drive follows a deterministic setpoint generated by the SIMATIC S7-1200 / S7-1500 / S7-1500T.

Setpoint path

1. Configure the PROFINET connection between the S7-1500 and the SINAMICS drive using a standard Telegram 1 (speed control) or Telegram 3 (8-bit process data, 2 PKW words) for simple speed control. For positioning, use Telegram 7, 9, or 110 per the PROFIdrive Profile Drive Technology standard.
2. Build a Technology Object in TIA Portal: TO_SpeedAxis or TO_SynchronousAxis depending on the application class.
3. Issue a velocity setpoint from the PLC program; the drive follows the S7-setpoint regardless of any STARTER activity.

Trace path

1. Start the SINAMICS Trace on r63 (actual speed), r80 (torque), and the STW/ZSW signals.
2. Simultaneously run an S7-Trace on the S7-1500 CPU to capture the S7-side setpoint and the actual values returned via the telegram.
3. Cross-correlate the two traces in DIAdem to obtain an end-to-end view of the closed loop.

Key parameters

Workaround 6: SINAMICS Web Server for Remote Monitoring

The SINAMICS G120 with CU250S-2 PN and the SINAMICS S120 with CU320-2 PN provide an integrated Web Server that can be read over any modern browser on port 443 (HTTPS) or 80 (HTTP). The Web Server exposes a subset of parameters including r63, r80, and the active setpoint, refreshed at 250 ms.

Because the Web Server is read-only, it does not assume master control. STARTER can keep the Control Panel active while a second browser window on the same PC (or a tablet on the same network) logs the parameters to a CSV file. The Web Server must be activated:

Access the Web Server at https://<drive-IP>/index.html. The page "Diagnostics > Trace > Signal Monitor" can be exported as CSV via JavaScript bookmarklet. For long-term logging, use a Python script with the requests library polling the JSON endpoint, or use a Node-RED dashboard.

Verification Procedure

After applying any of the workarounds, run the following verification to confirm that the drive does not drop out during a tab switch:

1. Bring the drive to a known state: command p970 = 1 ("Do not allow power-up to be reactivated without explicit command") only on S120 chassis drives; otherwise just issue a basic standstill check.
2. Issue ON/OFF1 from the active control path. The drive should report r2199.0 (Ready to switch on) and r2199.2 (Operation enabled) in the parameter list.
3. Open a second monitor view (Trace tab, Web Server, or scope software) for at least 10 minutes. Verify that r63 remains at the commanded setpoint, that r80 tracks the load, and that the SINAMICS diagnostic buffer (r0947) does not show F08501 (PROFIBUS master sign-of-life failure) or A08502 (control timeout).
4. Toggle the second view in and out of focus repeatedly. The drive should remain in operation; if it drops, record the timestamp of the drop and the parameter that flipped first (usually r899.0 — Master control by PLC).
5. Save the trace export and the SINAMICS diagnostic buffer (r0947 indexed 0..63) to a project folder.

Commissioning Checklist

Troubleshooting Matrix

Best Practices for Long-Term Data Logging on SINAMICS

1. Always back up the project before a trace session. Online > Save project to memory card creates a version-tagged ZIP of the entire drive image. Store a copy of the trace CSV alongside it.
2. Use r-parameters, not p-parameters, in the trace. Parameters prefixed with "r" are read-only runtime values; "p" parameters are writeable. Triggers on "p" are technically possible but can drive the drive into a writable state that blocks PLC ownership.
3. Reserve at least 250 µs of servo CPU for trace. On S120 with p0115[0] = 250 µs and a heavy trace, the controller's dead-time budget can collapse. Verify r9970.0 — computation time utilization — stays below 80 %.
4. For long-term logging, prefer the S7-1500 S7-Trace over the SINAMICS trace. The PLC trace can run for hours without consuming the drive's trace buffer and can capture the entire telegram (16 process-data words).
5. Document the master-control transitions in the SINAMICS diagnostic buffer. Set p0952 to log "control owner change" events and periodically save r0947 indexed 0..63 to the engineering database.
6. Disable the Web Server (p8981 = 0) and the PROFINET discovery mechanism (p8985 = 0) before returning the drive to production.
7. Update to the latest STARTER service pack. SP3 / SP4 patches frequently address tab-focus issues in newer Windows versions (e.g., the Windows 10 1903 and Windows 11 22H2 focus-management changes).

Field-Commissioned Notes

On a SINAMICS G120 with a CU250S-2 PN running firmware V4.7 SP3 under STARTER V5.4 SP3, the master-control release occurs within 50–80 ms of the Windows focus-loss event. The drop is so fast that operators typically attribute it to a "drive fault". A quick diagnostic is to enable r2199 in the parameter list: bit 6 (switch-on inhibit) and bit 4 (OFF2 active) often toggle together with the focus event.

On a SINAMICS S120 with a CU320-2 PN V5.2, the focus-loss behaviour is identical, but the Trace function can record at the servo cycle (125 µs) because the drive-clock is locked to the PROFINET IRT time. This makes S120 a far better platform for high-speed logging of current and torque waveforms than G120, which is locked to 4 ms in vector mode.

Operators moving to TIA Portal V18 with Startdrive V18 will note that the "Control Panel" inspector can be docked to the bottom pane of the project tree, so the trace and the control panel share the same parent window. This is the most reliable single-PC solution for engineers who can upgrade.

Related Parameter References

FAQ