SINAMICS Drive HMI Current Reading Above 100%: Root Cause and Fix

Problem Description: Drive Output Reports Above 100% on HMI

A 30 HP (22.4 kW) squirrel-cage induction motor drives an extruder from a SINAMICS variable-frequency drive rated at 60 A. The drive's analog output (typically the 0/4–20 mA or 0–10 V terminal on the Control Unit) is wired directly to a multi-touch HMI, where the load current is shown as a percentage. An S7-300 CPU 315-2 DP controls the line via PROFIBUS. Operators report that the HMI reading occasionally jumps above 100% even though the motor, by their observation, is not under unusually high mechanical load. The drive itself does not trip, and no SINAMICS fault or warning is raised on the same event.

This pattern — "HMI shows >100%, drive stays healthy, mechanical load looks normal" — is almost never a motor or insulation problem. It is a measurement-and-display problem in one of three places: the drive's analog-output scaling, the HMI's interpretation of the analog signal, or the EMC integrity of the wiring between them. The fix is therefore not at the motor; the fix is in the configuration and verification chain.

Defining "100%": What the Reference Value Actually Is

Before any parameter is touched, the meaning of "100%" must be pinned down. SINAMICS reports currents relative to a reference, and the analog output follows whichever signal you assign in p0771[0]. There are at least three different "100%" values active in a single drive:

If the HMI is mapped to a torque signal (r0080) or to DC-link voltage (r0026), the same percentage value means something completely different again. Verify in the HMI tag list which SINAMICS word is being scaled, then trace the word back to the drive parameter it was generated from.

For a 30 HP / 22.4 kW motor on a 400 V three-phase supply with an efficiency of ~0.90 and a power factor of ~0.86, the expected full-load line current is roughly:

I_line = P / (√3 × V_LL × η × cos φ) = 22 400 / (1.732 × 400 × 0.90 × 0.86) ≈ 41.6 A

If p2002 is left at the drive's 60 A nameplate value, then 100% on the analog output = 60 A, and a motor that is genuinely loaded to ~42 A will show ~70%. A reading above 100% means the drive is actually delivering more than 60 A at the output — which is well inside the 150% / 60 s overload envelope of most PM240 power modules, but is still a real overload event, not a display error.

Conversely, if p2002 has been inadvertently re-scaled to 40 A (e.g. by importing a project template), a real 50 A of motor current will display 125% even though the drive and motor are both fine. This single parameter accounts for the majority of "phantom >100%" cases on commissioned SINAMICS systems.

SINAMICS G120 System Overview for the 60 A / 30 HP Extruder Drive

The SINAMICS G120 family is a modular drive platform composed of a Control Unit (CU230P-2, CU240E-2, CU250S-2 etc.) and a Power Module (PM240, PM240-2, PM250). For a 60 A, 400 V class application of this size, the typical build is:

• Power Module: PM240-2 or PM240, frame size FSD/FSE, 60 A rated output (verify against the specific 6SL3210-1PE28-4UL0 or 6SL3224-0BE38-8UA0 catalog number on the rating plate).
• Control Unit: CU240E-2 PN or CU230P-2 (the latter is preferred for HVAC/pump/fan, but the analog-output set is identical).
• Reference: SINAMICS G120 Brochure (PDF) and the SINAMICS product page describe the modular combination options and the current ratings per frame size.

The analog output is implemented on the Control Unit (terminals 12/13 or 14/15 depending on variant), and the firmware for the G120 family evolves through releases — typically V4.4, V4.5, V4.6, V4.7 at the time of writing. Parameter numbers used in this article (p0771, p2000, p2002, p0776–p0781) are stable across the SINAMICS platform, but the default values and the availability of certain indices can differ between firmware versions. Always cross-check against the parameter list (DPL) that matches the firmware actually loaded on the Control Unit. The version is read from r0018 or via the SINAMICS web server homepage.

Root Cause Matrix: Why an HMI Reads More Than 100%

In field practice, cause #2 (p2002 mis-set) and cause #4 (cold-extruder startup) together account for the majority of tickets that look exactly like the one described in the source. Cause #5 and #7 are the next most common. Causes #1, #3, #6, and #8 are configuration errors introduced during commissioning or template cloning.

Diagnostic Workflow

1. Capture the firmware of the Control Unit from r0018 and the catalog number of the Power Module from the rating plate. Record the parameter list version.
2. Read p0771[0] and p0776[0] on the drive. Confirm the analog output is sourcing a current actual value and that the electrical type matches what the HMI expects.
3. Read p0777[0], p0778[0], p0779[0], p0780[0], and p0781[0]. Compare the value at p0778 against p2002 and p0305 — they should be consistent with the HMI's expected full scale.
4. Read p2002 (reference current for percentage values) and p2000 (reference speed for percentage values). Confirm p2002 is the rated output current of the Power Module, not a hand-typed value from a project template.
5. Trigger the integrated SINAMICS trace on r0068 (or r0027) at the 100% threshold. If the trace does not fire while the HMI shows >100%, the HMI is being driven by a signal the drive never produced — the fault is downstream.
6. Measure the analog-output terminals with a calibrated multimeter (Fluke 87V or equivalent) at the HMI end. Confirm current/voltage matches the drive's reported value.
7. Measure the motor terminal current with a true-RMS clamp meter (Fluke 381, Hioki CM3286, or AEMC SR759) on one phase conductor. Compare to drive r0068.
8. Inspect the HMI / WinCC Flexible / TIA Portal project — the linear-scaling block on the analog tag must map the full-scale electrical input to the full-scale engineering unit (e.g. 20 mA = p2002 A, 4 mA = 0 A, 0 mA = error).

Configuring the SINAMICS Analog Output Correctly

The analog output on a SINAMICS Control Unit is a single channel (or two, on CU250S-2) that can be re-routed in software. The minimum set of parameters that must agree are:

For a 4–20 mA loop driving a 0–100% HMI bar, the simplest interpretation is 0% = 0 A at 4 mA and 100% = p2002 A at 20 mA. If p2002 has been set to the motor's nameplate current (e.g. 42 A for a 30 HP motor on 400 V), the bar will read 100% exactly at motor FLA. If p2002 has been set to the drive's rated current (60 A), the bar will read ~70% at motor FLA and will only saturate at 100% during genuine overload. Choose p2002 deliberately and document the choice in the project.

HMI / WinCC Flexible Scaling for the 4–20 mA Loop

On the HMI side, the analog input card is normally a Siemens Comfort Panel (TP1200, KTP1200) or a third-party multi-touch panel with a 0/4–20 mA input. The scaling block in WinCC Flexible or TIA Portal is configured as a linear transformation:

• Input range: 0 to 27648 (raw count for a Siemens SM 1231 / 6ES7 analog input), or 0–65535 for 0–10 V / 0–20 mA on a Comfort Panel direct input.
• Output range (engineering units): 0 to p2002 in A, or 0 to 100 in %.
• Live zero: If the loop is 4–20 mA, the lower count is 0 (for 4 mA) and 65535 / 27648 (for 20 mA). Wire a 2-point linear interpolation in the HMI tag's "Linear scaling" properties.

For an operator-facing percent display, scale directly: Display [%] = ((raw − raw_zero) / (raw_full − raw_zero)) × 100, where raw_zero and raw_full correspond to 0% and 100% of p2002. Do not chain a percent-to-Amp conversion on top of a percent-to-percent conversion; double-scaling is a frequent root cause of phantom >100% reads.

S7-300 AI Module and PLC Tag Wiring

If the analog output of the drive is wired into the S7-300 (SM 331 analog input module, e.g. 6ES7331-1KF02-0AB0) and the PLC forwards the value to the HMI over PROFIBUS or PROFINET, the PLC's analog-input channel must also be configured correctly. The S7-300 SM 331 supports many measurement ranges via hardware jumpers (DIP / solder bridges on the side of the module) and software (STEP 7 HW Config → Properties → Inputs → Measurement type). The measurement type must be set to "I" (current) and the range to either 0–20 mA or 4–20 mA. If the hardware is jumpered for voltage and the software is set to current, the reading will be wrong by a factor of 5 (5 V = 20 mA on the shunt) and can read above 100% in random ways.

The PLC's PIW (process input word) is then normalized in the user program: Normalized = (PIW × 27648) / 27648 for 0–20 mA, or Normalized = ((PIW − 0) × 100) / 27648 for a 0–100% bar. The S7-300 CPU 315-2 DP supports both PROFINET and PROFIBUS, so the HMI is usually a Comfort Panel on PROFINET and the drive a SINAMICS G120 on PROFIBUS — but the analog signal is a parallel path, not a bus signal. Verify in the HMI tag list which path is the source of the bar.

Using the SINAMICS Internal Trace to Isolate the Fault

The single most useful diagnostic tool is the integrated trace function. The SINAMICS trace can be opened from:

• STARTER (the offline/online commissioning tool) for SINAMICS G120 — Trace menu, up to 8 channels, 8 ms to 10 s sample time.
• The web server of the CU230P-2 or CU240E-2 (firmware V4.6 and above) — Diagnostics → Trace, with the same capture capability but without a software install.
• TIA Portal (since V14) — drive project → Trace, with online connection to the Control Unit.

Configure the trace as follows:

1. Channel 1: r0068 (absolute current actual, unsmoothed) — the wire-truth current.
2. Channel 2: r0027 (smoothed current) — the analog-output value.
3. Channel 3: r0077 (torque actual) — for cross-check.
4. Channel 4: p0771 (the configured source) — for verification.
5. Trigger: immediate, with a pre-trigger of 10% so you capture the rise.
6. Duration: 30 s, plenty for an extruder cold-start.

Start the trace, run the extruder through a normal cycle (or simulate a high-load event by tightening the die back-pressure valve). When the HMI shows >100%, examine the trace:

• If r0068 (the real current) is at or above 60 A (or above p2002), the drive is genuinely in overload. The HMI is correct.
• If r0068 is at 42 A and r0027 (the analog source) is at 42 A, but the HMI shows >100%, the scaling block in WinCC / TIA is wrong.
• If r0068 and r0027 agree but the trace shows them clipping at the analog output's saturation, the issue is p0778 / p2002 — the HMI percentage is correct relative to the analog-output full scale, but the analog-output full scale is wrong.
• If r0068 / r0027 show no spike but the HMI does, the analog loop is picking up EMI or the HMI is using a stale / wrong tag.

The trace will resolve the problem in one run, without disconnecting the motor. The advice offered in the source — "set up the trace, trigger at 100%" — is exactly the right first move.

Independent Motor-Terminal Current Measurement

To confirm what the drive reports, measure the actual line current at the motor terminal box with a true-RMS clamp meter. Clamp around one phase conductor only (not all three — three-phase clamps exist but are not necessary for a sanity check and can introduce their own scaling errors if the phases are imbalanced). The reading should equal the drive's r0068 within ±2%.

For a 30 HP, 400 V three-phase motor, expected full-load current is in the 38–42 A range (see formula above). During the extruder screw warm-up, expect transient peaks of 50–65 A for several seconds. If the HMI shows 110% during that transient and the clamp confirms 65 A on a 60 A p2002, the system is behaving correctly — p2002 has been left at the drive's nameplate rating, and the operator should be informed that the bar will occasionally read above 100% during cold starts. If p2002 has been set to p0305 = 42 A, the bar will read 150% at the same instant, which is alarming to operators and almost always the cause of an unnecessary ticket.

Do not use a Hall-effect clamp with low DC accuracy below 10 A on a 30 HP drive; the DC component at light load can dominate and many low-cost clamps filter it out. A current transformer (CT) clamp is fine for the AC line current but will not see the DC component of a sensorless-vector drive at very low speeds.

Extruder Load Profile: Why "Sudden Spikes" Are Normal

Single-screw and twin-screw extruders are not constant-torque loads. The current profile of a typical extrusion cycle is:

1. Cold start (0–120 s): Screw friction and un-melted polymer mass produce a torque peak of 150–200% of rated. Current is at 110–180% of motor FLA. The drive's overload management (typically 150% / 60 s) is sized for exactly this transient.
2. Warm-up ramp (2–10 min): Torque falls to 90–110% as polymer melts and the melt film lubricates the barrel wall.
3. Steady-state extrusion: 70–100% torque, current at 70–100% of FLA, depending on throughput and back pressure.
4. Die restriction or screw blockage: Torque can climb to 130–160% within seconds, current to 110–140% of FLA. The drive's I²t model (r0034) will rise and may issue warning A07805 "Motor overload" if it crosses the configured threshold (default 100%).
5. Screw clearing / purge: Torque drops to 30–50% while polymer empties; current is light.

If the HMI reading is being interpreted as a percentage of motor nameplate (p0305 = 42 A for 30 HP), the bar will read 100% at FLA, 150% at typical cold-start peak, and 180% at the first die blockage. None of these are faults; they are the working envelope of an extruder drive. Operators familiar with V/Hz drives on extruders expect to see transient over-100% values. Operators who learned on servos or on field-oriented vector drives with a separate torque limit may misinterpret the bar as a fault indicator.

EMC, Shielding, and Analog-Loop Grounding

Long analog cables routed alongside VFD output cables (motor cables) will pick up common-mode noise from the IGBT switching edges (typically 2–16 kHz on a PM240). The induced voltage on the analog loop can add tens of millivolts — enough to push a 0–10 V signal to 10.2 V briefly, which the HMI will read as >100%. The fixes are standard but mandatory:

• Use a shielded twisted pair for the analog output. Ground the shield at the cabinet end only, with a 360° EMC gland on the panel entry. Do not ground the shield at both ends unless a heavy bonding conductor is run between the two grounds to break the ground loop.
• Route the analog cable in a separate tray from the motor cable, with a minimum 200 mm separation. Cross motor and analog cables at 90° when they must intersect.
• Install a ferrite clamp on the analog cable near the drive end (Würth 74270097 or equivalent, ≥ 100 Ω at 25 MHz).
• Verify that the drive's analog-output terminal is referenced to the same ground potential as the HMI's analog-input terminal. A floating HMI input (no return path) will drift. The SINAMICS Control Unit has a dedicated analog ground terminal (M) that must be wired to the HMI's analog ground — not to chassis ground.
• Where the cable run exceeds 10 m, use a 4–20 mA current loop instead of 0–10 V. The current loop is immune to voltage drop and to most common-mode noise.

The Siemens SINAMICS G120 installation guidelines specify that signal cables and power cables must be separated by at least 200 mm and that analog signals must use shielded cable. The same document is the reference for the cabinet layout.

Verification Procedure After the Fix

1. Re-confirm p0771[0] = r0027 (or r0068) and p0776[0] matches the HMI input type.
2. Set p0777[0] = 0 A, p0778[0] = p2002, and the corresponding p0780[0] / p0781[0] for the chosen current/voltage mode. Save the parameters to the non-volatile memory with p0977 = 1 (or "Copy RAM to ROM" from the operator panel).
3. Re-launch the SINAMICS trace. Verify r0068 (real current), r0027 (analog-output source), and the HMI display are in lock-step across a 30 min extruder run.
4. At zero speed, the analog output should be 0 mA / 4 mA / 0 V depending on configuration. At motor FLA, the analog output should be exactly 20 mA × (FLA / p2002). For a 42 A motor on a 60 A p2002, that is 14 mA, which the HMI should display as 70%.
5. Document p2002, p0771, p0777, p0778, p0779, p0780, p0781 in the project as-built. The next person who inherits the system will read this and avoid the same trap.

Field Reference Summary

The bulk of the source question — "where is the problem and how do I solve it" — is answered by three settings: p2002 = rated drive current (or rated motor current, your call — document it), p0771 = r0027, and the HMI linear-scaling block mapping the live zero correctly. The trace function is the verification tool that proves the fix. The clamp meter on the motor terminal is the independent witness. With those three in agreement, the HMI cannot lie.

Frequently Asked Questions