Resolving SIMOREG F024 Encoder Error 6RA24/6RA70 Diagnostic Guide

1. Problem Statement: F024 Encoder Error on SIMOREG DC Drives

A SIMOREG series DC drive configured for encoder-based speed feedback trips immediately on run command with fault F024 (Encoder Error). The encoder in question is a Leine&Linde (or equivalent) incremental encoder, type EL40A000Z5/28P6X6PR2, rated 2000 pulses per revolution (PPR). Two distinct failure modes are reported:

• With the encoder configured at its true rating of 2000 PPR, the drive trips F024 almost immediately after the start command.
• With an artificially low setting of 500 PPR, the drive runs for approximately five minutes before the trip occurs.
• At low speeds the motor exhibits cogging — a pronounced pulsing or stepping pattern — before settling into smooth rotation.

The encoder, when cross-installed onto another healthy drive in the same network, functions correctly. This eliminates a defective encoder as the root cause and shifts focus to the drive itself, its parameterization, wiring, and the mechanical coupling.

2. Drive Family Identification and Source-of-Truth

The SIMOREG DC-master family covers several generations. Each generation has a distinct firmware, parameter set, and terminal layout. Confirming the exact drive before applying any encoder configuration is mandatory because parameter numbers, fault codes, and terminal assignments differ.

3. F024 Fault Definition Across SIMOREG Generations

Fault codes F024 and F042 are often confused in field reports — the operator's notes explicitly call out a typo where F042 was written in place of F024. They are distinct faults with distinct root causes:

The behavioural evidence — immediate trip at correct PPR, delayed trip at incorrect PPR — is consistent with F024 being driven by a feedback scaling or mechanical-load anomaly rather than a wire break. The artificial reduction to 500 PPR scales down the expected speed/feedback relationship, which delays the out-of-tolerance detection by the monitoring block.

4. Encoder Hardware: EL40A000Z5/28P6X6PR2 Specifications

The encoder code segments are decoded as follows. The model is a heavy-duty incremental encoder with internal detection electronics, suitable for industrial DC drives.

Operating parameters:

• PPR: 2000 (true rating; 4× quadrature resolution gives 8000 counts/rev at the controller input).
• Supply: typically +5 V DC or +24 V DC depending on output stage; verify the specific variant.
• Output: differential, push-pull (HTL) or RS-422 (TTL) depending on Z5 variant — confirm before connecting to the SIMOREG pulse-encoder input.
• Maximum frequency: 100–200 kHz typical. At 2000 PPR and a top motor speed of 1500 rpm, the channel frequency is 50 kHz — well within spec.

5. Wiring Topology Per Sheet 10/3 (Pulse Encoder, Internal Detection)

The wiring diagram on sheet 10/3 of the SIMOREG K manual describes the "Pulse encoder, internal detection" topology — that is, the SIMOREG supplies power to the encoder and reads its differential quadrature outputs. The connector pinout varies between 6RA23 and 6RA70 generations, but the signal flow is identical.

Critical wiring rules per sheet 10/3:

1. Use a twisted-pair shielded cable — minimum Cat 5 / 24 AWG, ideally dedicated encoder cable (e.g., Lapp EKM, Helukabel). Run separately from power cables; minimum 200 mm parallel clearance.
2. Connect the shield to PE at the SIMOREG end only. Do not bond at the encoder end — this avoids ground loops that inject common-mode noise.
3. Differential pairs must be twisted together: A with A\, B with B\, Z with Z\. Do not split pairs across cables.
4. Total cable length should not exceed the encoder manufacturer's specification (typically 30 m for HTL, 100 m for RS-422 with proper cable).
5. Confirm that the SIMOREG encoder-input card is configured for the encoder's output voltage level (5 V TTL or 24 V HTL) via the relevant DIP switch or jumper.

6. Root Cause Matrix for Immediate-Onset F024 vs Delayed F042

The following matrix maps the symptom behaviour to probable causes, ranked by the operator's evidence pattern (immediate trip at 2000 PPR, delayed trip at 500 PPR, cogging at low speed).

7. Parameter Configuration: PPR and Feedback Source Selection

The following parameters are the canonical SIMOREG settings for pulse-encoder feedback. The exact parameter numbers differ between 6RA23 and 6RA70 generations; always cross-check against the parameter manual for your drive.

Read-modify-write sequence (6RA70 via PMU / OP1S):

// Access PPR parameter
P083 = 2000            ; pulses per revolution, exact nameplate value

// Verify feedback source
P140 = 1               ; 0 = armature EMF, 1 = pulse encoder (example value)
                       ; consult P140 enumerations in compendium manual

// Save to non-volatile memory
P052 = 1               ; execute EEPROM save (if supported on this firmware)

8. Step-by-Step Diagnostic Procedure

The procedure below follows the evidence-driven path that produced a successful diagnosis on a similar 6RA23 / 6RA70 system.

1. Confirm the drive type. Photograph the nameplate; read order number; locate the matching parameter manual.
2. Verify the encoder independently. Power the EL40A000Z5 with a 5 V or 24 V bench supply (per encoder variant); observe A, B, Z on an oscilloscope while rotating the shaft by hand. Expect clean 50% duty-cycle square waves, 90° phase shift between A and B, one Z pulse per revolution.
3. Inspect the encoder mount. With the encoder removed, dial-indicator the motor shaft for total indicated runout (TIR). Typical acceptance: < 0.05 mm. A bent or eccentric shaft will modulate the air gap and produce pulse-amplitude variations that mimic an encoder fault.
4. Inspect the coupling. Loose jaw couplings, worn rubber spiders, and keyless shaft locks with eccentric clamping all induce encoder noise. Replace with a zero-backlash flexible coupling rated for the motor's torque.
5. Verify the wiring per sheet 10/3. Confirm differential pair integrity; check shield bonding at SIMOREG end only; confirm correct supply voltage to the encoder.
6. Confirm feedback-source parameter. Drive must be set for pulse-encoder feedback, not armature-EMF feedback, if speed control is required from the encoder.
7. Run uncoupled. Disconnect the load; command a low-speed reference (5–10% rated); observe r000 (speed actual) on the PMU. If F024 does not occur, the fault is mechanical-load induced.
8. Run in voltage feedback (EMF). If uncoupling is impossible or the mechanical system cannot be tested, switch the speed feedback source to armature-EMF (voltage feedback) and run at no-load or light-load conditions. EMF feedback uses the back-EMF as the speed proxy and bypasses the encoder.
9. Capture the trip context. On F024, freeze the fault buffer (r047 / fault memory on 6RA70) to read the speed actual value, armature current, and armature voltage at the moment of trip. This confirms whether the actual value was present, out of tolerance, or zero.
10. Swap the input card. If all other causes are eliminated, hot-swap the pulse-encoder option card between the affected drive and a healthy drive to isolate the fault to the input electronics.

9. Mechanical Decoupling Verification

Mechanical disturbance is the single most common cause of an encoder-fitted motor that fails its feedback integrity check only on one of multiple drives — especially when the drive's input card, encoder, and wiring have already been independently validated.

The decoupling test is non-destructive and requires only removal of the load-side coupling. Expected outcomes:

• No-load run clean: confirms load-side disturbance; inspect gearbox, belts, chain, or downstream machinery for binding.
• No-load run still trips F024: confirms drive-side or encoder-side issue; proceed to voltage-feedback fallback.
• No-load run cogging persists: inspect encoder mount and shaft concentricity; replace the flexible spider coupling.

10. Voltage-Feedback Fallback Mode

When uncoupling is not possible (coupled process, no available spare motor, locked-out maintenance window), switching to armature-EMF (voltage) feedback bypasses the encoder entirely. The drive computes speed from the back-EMF constant of the motor:

n_actual = (V_armature - I_armature * R_armature) / kE

Voltage feedback is acceptable for constant-torque loads but has reduced low-speed accuracy and no position information. For applications requiring precise low-speed regulation, voltage feedback is a diagnostic step, not a permanent solution.

To switch to EMF feedback on 6RA70: set the speed-actual-source parameter to the EMF value (typically P140 = 0 or a labelled enumerator "EMF"). Verify that the IR-compensation parameter (typically in the P150–P160 range) is set to the measured armature resistance plus brush voltage drop; otherwise low-speed accuracy will suffer.

11. Cogging at Low Speed: Tach Ripple, Resolution, and Mechanical Resonance

The reported low-speed cogging — the motor stepping in pulses rather than rotating smoothly — is a separate but related symptom. Three contributors must be considered:

1. Encoder resolution mismatch. At 2000 PPR with no quadrature multiplication, the speed-loop controller receives 2000 edges per revolution. At 30 rpm, that is one edge every millisecond — borderline for high-gain current-loop controllers. Verify whether the drive multiplies quadrature internally; if so, 2000 PPR gives 8000 counts/rev which is normally sufficient.
2. Speed-controller bandwidth too high. High proportional gain at low speed amplifies feedback quantization. Reduce the speed-controller Kp by 30% and verify whether cogging diminishes.
3. Mechanical resonance in the load. Coupling stiffness, shaft inertia, and gearbox play form a second-order mechanical system. If its natural frequency coincides with the speed-loop bandwidth, oscillation results. The cure is either detuning the speed loop (lower Kp, slower Tn) or adding a filter to the speed-actual signal.

Replace the "500 PPR" workaround with the correct 2000 PPR setting only after the F024 root cause is resolved. The artificial PPR reduction masks the symptom but degrades speed-loop performance and may introduce additional F024 trips under transient load.

12. Verification Checklist and Commissioning Sign-Off

Confirm the following before returning the drive to production:

Document the encoder PPR, feedback-source parameter, encoder model, and the fault-buffer snapshot in the maintenance log. This baseline accelerates diagnosis on any future trip.