Migrating Elcis 90A HTL Encoder from SIMOVERT to SINAMICS G120

1. Overview

Field retrofits that replace a legacy SIMOVERT MasterDrive with a SINAMICS G120 control unit frequently surface the same question: can the existing incremental encoder be reused without modification? This article documents the migration of an Elcis 90A-1024-1230-BZ-C-VL-R-01 incremental encoder from a SIMOVERT MasterDrive to a SINAMICS G120 CU250S-2 DP (Control Unit). The encoder is a 1024-pulse-per-revolution, HTL-output, push-pull device with index pulse and quadrature channels. It is electrically compatible with the CU250S-2 encoder interface when wired as unipolar HTL, configured through parameter p0407 (encoder type) and p0408 (pulses per revolution), and supplied from an external 15 V DC source such as a SITOP or LOGO! Power PSU.

The content below addresses three recurring field mistakes that arise during this migration:

1. Confusing the manufacturer term "Bidirectional + zero" with differential (bipolar) driver topology.
2. Misreading the encoder datasheet voltage rating and selecting an unsafe supply rail.
3. Leaving the encoder interface parameters at SIMOVERT default values, which prevents the CU250S-2 from interpreting the HTL signal correctly.

Where useful, links to the official Siemens documentation are provided for cross-reference during commissioning.

2. Encoder Identification: Decoding the 90A Part Number

The full ordering code is 90A-1024-1230-BZ-C-VL-R-01. Each token has a defined meaning in the manufacturer's catalog convention; for the migration it is sufficient to interpret the four fields that govern electrical compatibility with the SINAMICS G120:

The "1230" token is the dominant piece of evidence used to select the HTL input stage on the G120. Decoding it as "12 V to 30 V, HTL" eliminates any concern that the encoder must be supplied with 5 V TTL.

3. HTL vs TTL vs "Bidirectional": Clarifying the Misconceptions

Three terms recur in the encoder's catalog text and are routinely confused during migration. The table below establishes the correct interpretation.

4. CU250S-2 Encoder Interface Specifications

The CU250S-2 Control Unit is the second-generation encoder-capable SINAMICS G120 variant. It supports two encoder interface families, selectable in software. The relevant electrical limits are summarized below; refer to the SINAMICS G120 CU250S-2 Operating Instructions for the full specifications.

For the Elcis 90A-1024-1230-BZ-C-VL-R-01, the encoder is wired as HTL unipolar on X521. The CU250S-2 will be configured to interpret A/B/Z without the inverted tracks. In STARTER/Startdrive the wizard exposes this selection as "Encoder type = HTL unipolar" with a voltage dropdown of "5 V / 24 V"; selecting 24 V in the expert list actually enables the wider 13.5–30 V hardware window. This dual representation of the same hardware range is intentional but is a frequent source of confusion in the field.

5. Wiring Procedure: SIMOVERT MasterDrive → G120 CU250S-2

5.1 Prerequisites

• SIMOVERT MasterDrive powered down and locked-out / tagged-out (LOTO).
• External 15 V DC supply (e.g., LOGO! Power 24 V reduced with a voltage divider is not acceptable; use a dedicated 15 V regulated PSU such as 6EP1331-1SH13 or a LOGO! Power 15 V variant).
• Encoder cable with at least 5 conductors: +V_supply, GND, A, B, Z. Shielded twisted-pair (STP) recommended; overall shield bonded at the cabinet entry only.
• STARTER V5.x (legacy) or Startdrive in TIA Portal (current) commissioning software installed and online to the CU250S-2 via PROFIBUS or PROFINET.

5.2 Encoder Connector Pinout (Elcis 90A cable end)

5.3 Wiring Sequence

1. Verify the SIMOVERT MasterDrive is de-energized and the DC bus is discharged (typically 5 minutes after power-off).
2. Identify the encoder cable on the MasterDrive side and label each conductor with the function (A, B, Z, +, -).
3. Disconnect the cable from the MasterDrive sub-D connector. Note the original routing and tie-wraps so the mechanical layout can be reproduced.
4. Route the cable to the G120 cabinet. Add service loops of ~30 cm at both ends to ease future maintenance.
5. At the encoder, connect the conductors to the Elcis 90A terminal block (or M23 connector, depending on the "R" variant) following the table in §5.2.
6. At the cabinet end, terminate +V_supply and GND to the 15 V PSU. Bond the cable shield to the cabinet PE bar.
7. Wire the encoder signals to the CU250S-2 X521 sub-D connector:

X521 (sub-D 15-pin, female) — Encoder input HTL unipolar
  Pin 1  : GND (encoder supply return)
  Pin 2  : not used (P_24V sense; do NOT connect encoder supply here)
  Pin 6  : Encoder A
  Pin 7  : Encoder B
  Pin 8  : Encoder Z (index)
  Pin 9  : not used (A\ - leave open)
  Pin 10 : not used (B\ - leave open)
  Pin 11 : not used (Z\ - leave open)
  Pin 13 : not used (HTL_5V; only for TTL stage — DO NOT connect to 15 V)
  Pin 14 : not used
  Pin 15 : not used
  Shell  : Cable shield → cabinet PE

8. Verify continuity with a multimeter on each conductor; verify shield-to-PE continuity only at the cabinet end (high-impedance reading to encoder housing acceptable).
9. Power on the 15 V PSU only; measure 14.5–15.5 V at the encoder terminals under no-load.
10. Power on the CU250S-2 and proceed to parameter configuration.

6. Parameter Configuration in STARTER / Startdrive

The CU250S-2 encoder interface is configured through parameters p0400 (encoder type selection), p0407 (encoder mode / electrical interface), p0408 (pulse count), and p0410 (encoder inversion). For the Elcis 90A-1024 HTL encoder the following settings apply. Refer to the STARTER commissioning tool documentation and the Startdrive for TIA Portal documentation.

6.1 Wizard Steps (Startdrive, TIA Portal V17 or later)

1. Open the project → CU250S-2 device → "Commissioning" → "Configure drive".
2. Select the control mode (e.g., "Vector control with encoder" for closed-loop speed/torque control).
3. In the encoder step, choose "Incremental encoder" as Encoder 1.
4. In the voltage dropdown, select 24 V (which internally enables the 13.5–30 V window).
5. Set the pulse count to 1024.
6. Enable "Use zero mark" (index) only if the application references it (e.g., homing on index).
7. Complete the wizard and download the configuration to the drive.

6.2 Manual Parameter Entry (STARTER)

; In the expert list, set:
p0400[0] = 1       ; incremental encoder
p0404[0] = 1       ; enable evaluation
p0407[0] = 0x01    ; HTL unipolar
p0408[0] = 1024    ; pulse count
p0410[0] = 0       ; no signal inversion

; Copy RAM to ROM to persist:
p0971 = 1          ; save parameter set non-volatile

7. Commissioning Verification

1. Power-on check. Energize the 15 V PSU and the CU250S-2. Confirm r0002 = "Operation enable" is reachable.
2. Encoder self-test. From STARTER/Startdrive, run "Control panel" → "Take over drive". Issue a low-speed positive setpoint (e.g., 50 rpm). Verify r0021 (actual speed) tracks r0062 (speed setpoint) within the acceleration ramp.
3. Trace the raw encoder signal. Open the trace tool and record r0061 (speed actual, encoderless) and r0063 (actual speed, with encoder). Manually rotate the shaft at constant speed; both traces should be equal, confirming the encoder is being decoded.
4. Index verification. Configure a trace on r0480 (encoder 1 zero-mark events). Rotate the shaft one full turn. r0480 should increment by 1 per revolution. A missed or doubled count indicates the Z wire is loose, the threshold is wrong, or the index signal is shorted to A or B.
5. Direction check. Command a positive setpoint and verify r0063 is positive. If negative, swap A and B at X521 or invert via p0410.0 = 1.
6. Fault acknowledgment. Confirm F3x11 (encoder fault) and F3x18 (encoder speed mismatch) do not appear. If F3x18 triggers during acceleration, increase p0420 (encoder max speed for F3x18 detection) to 1.25 × the maximum operating speed.
7. Mechanical alignment of the zero mark. If homing relies on the index, verify the index angle against a known reference. Mechanical alignment of the zero pulse is specified by the trailing "01" in the part number; for a different alignment use a variant with a different trailing digit.

8. Troubleshooting Matrix

9. Field-Notes and Edge Cases

9.1 Why the 5 V / 24 V dropdown is misleading

On the CU250S-2 the encoder wizard and the expert list show only two voltage options: 5 V and 24 V. Internally, the HTL receiver is a wide-range comparator that accepts anything between 13.5 V and 30 V. Selecting 24 V sets the appropriate hysteresis and pull-up configuration; selecting 5 V does not mean the hardware is restricted to 5 V — it biases the receiver toward 5 V logic thresholds, which still accepts a 15 V signal but with reduced noise margin. The robust choice is always 24 V in the expert list.

9.2 When to keep the inverted tracks

If the same encoder family is later upgraded to a variant with differential outputs (e.g., 90A-1024-1230-BZ-D-VL-R-01 where D = line driver with inverted pairs), wire the inverted tracks to X521 pins 9/10/11 and select "HTL bipolar" in p0407. This adds immunity to common-mode noise on long cable runs (> 25 m) and is recommended for plant-floor installations with VFD-emitted EMI.

9.3 Why not 5 V TTL?

Although the 88C30 driver can in principle be operated from 5 V, the encoder's "1230" token mandates 12–30 V. Supplying 5 V violates the encoder's specification and is not supported by the manufacturer. The CU250S-2's TTL stage (X521 pin 13 = +5 V encoder supply) must not be used with this encoder.

9.4 Maximum speed calculation

The maximum mechanical speed is constrained by the CU250S-2's 500 kHz per-channel limit:

f_channel = (rpm / 60) × PPR
rpm_max   = (f_max × 60) / PPR
          = (500_000 × 60) / 1024
          ≈ 29_297 rpm

For the 1024 PPR Elcis encoder the CU250S-2 will decode correctly up to ~29 300 rpm. In practice the encoder's own mechanical limit (typically 6000 rpm for the 90A series) is the binding constraint, so the 500 kHz limit is not reached.

9.5 Cable length guidelines

9.6 Compatible SINAMICS control units

The procedure documented here applies to any SINAMICS platform with an HTL encoder interface: CU250S-2 (this article), CU310-2, CU320-2 with SMC30 sensor module, and the SINAMICS V90 servo drive. The parameter numbers (p0400, p0407, p0408) are consistent across these platforms, simplifying cross-platform commissioning.

9.7 Safety note

10. FAQ