Splitting 1Vpp Encoder Signals for Siemens 840D Spindle Feedback

Splitting 1Vpp Encoder Signals Between Bosch Rexroth IndraDrive and Siemens SINUMERIK 840D

Frameless IndraDyn H spindle motors from Bosch Rexroth typically ship with a 1 V_PP sine/cosine encoder that the matching IndraDrive closes its velocity loop against. When the same machine integrates a Siemens SINUMERIK 840D controller that also needs 1 V_PP feedback for spindle actual-value display, thread cutting, rigid tapping, or spindle positioning, the integrator is forced to derive two clean 1 V_PP signals from a single physical encoder. This application note documents the signal conditioning, connector conversion, and commissioning choices that work on a real retrofit, with particular attention to the Heidenhain IBV 606 signal doubler, the Siemens 611D 17-pin encoder socket, and the HLA module path inside the 840D firmware.

1. The Signal Compatibility Problem

The encoder in question is a 1 V_PP differential analog device. Two sine currents modulated 90° apart (often 11 µA_PP referenced through 1 kΩ, or 1 V_PP across 120 Ω at the receiver) are superimposed on the supply wires. A typical pin assignment follows the Heidenhain 12-pin mini connector convention.

The Bosch Rexroth IndraDrive "emulated encoder output" (often labelled Emu or --OUT) produces a 5 V TTL/RS-422 square-wave signal derived from interpolating the 1 V_PP input. That TTL signal is what the IndraDrive exposes on its second encoder socket. The 840D, however, will not accept this TTL stream as a spindle actual value when the configured encoder type is set to 1 VPP - the interpolation, commutation and signal-quality diagnostics inside the Siemens 611D module rely on the analog sine waveform, not the digital square wave.

2. The Three Practical Approaches

2.1 Passively Y-splitting the encoder cable

Wiring the encoder to two receivers in parallel works only if the second receiver presents a high enough impedance that the voltage divider formed by the two inputs does not attenuate the 1 V_PP signal below the receiver's recognition threshold (typically 0.6 V_PP minimum for Siemens and Heidenhain front ends). Both IndraDrive and Siemens 611D encoder inputs present roughly 120 Ω differential termination. Two parallel 120 Ω terminations drop the signal to half, well below the usable amplitude.

Conclusion: a passive Y-split is not viable for two simultaneously terminating receivers unless one receiver is placed in high-impedance (un-terminated) mode. The IndraDrive analog encoder input has no such option.

2.2 Buffering the 1 V_PP signal with Heidenhain IBV 606

The Heidenhain IBV 606 (and the related IBV 6600/IBV 6100 families) is a single-input, dual-output interpolator/buffer for 1 V_PP signals. The input is a 12-pin Heidenhain connector wired to the encoder; both outputs are individually programmable for 1 V_PP or RS-422 TTL, with independently settable subdivisions. For a Rexroth/Siemens retrofit the canonical wiring is:

• Encoder → IBV 606 input using a standard 12-pin Heidenhain cable.
• Output A (1 V_PP) → IndraDrive analog encoder input (X4 or X8, depending on firmware generation) using the cable that ships with the IndraDrive, terminated in the D-sub connector the drive expects.
• Output B (1 V_PP) → Siemens 611D spindle encoder socket via a 12-pin-to-17-pin adapter. See section 4.

The IBV 606 is powered from the encoder cable (5 V supplied on pins 12 and 4, returned on pin 10) or from an external 5 V supply on the dedicated power pins. It regenerates clean, low-jitter 1 V_PP signals at each output with a propagation delay typically under 250 ns, well below the latency Siemens uses for its 4×/8×/16× interpolation in the 611D module.

2.3 Converting the IndraDrive 5 V TTL output back to 1 V_PP

The IndraDrive's emulated TTL output can be re-shaped into a 1 V_PP sine wave with a passive LC reconstruction filter, or fed through a Heidenhain IBV 102 or a third-party resynthesizer. Siemens documentation explicitly notes that this configuration is not supported; the field reports, however, indicate that on a Siemens 611D-F module the TTL stream can be accepted if the line receiver on the 611D card is forced to TTL mode and the controller is told to expect TTL. The risk is twofold: the TTL stream contains no commutation information usable by the 840D for vector spindle control, and any jitter from the IndraDrive interpolation is passed through unchanged.

3. Heidenhain IBV 606 - Functional Block Diagram

4. Connector Conversion: 12-pin Heidenhain to 17-pin Siemens

Heidenhain encoders and the IBV 606 use the standard 12-pin mini round connector (M23, 12-pin, clockwise). Siemens SIMODRIVE 611D modules use a 17-pin combo-D connector for the spindle encoder (X411 on the resolver/encoder module). The pin mapping must preserve the 5 V supply, the 0 V return, the four 1 V_PP signals (A+, A-, B+, B-, and on absolute encoders the R+/R- index) and leave any unused cable shield pins tied only at the receiver end.

The Heidenhain 12-pin connector follows Heidenhain's published pin-out convention. The Siemens 17-pin connector layout and the encoder type parameters are documented in the SINUMERIK 840D Commissioning Manual and in the SIMODRIVE 611D Function Manual. Cable impedance must be maintained at 120 Ω differential, twisted-pair, with shields bonded at one end only to avoid ground loops between the IndraDrive chassis and the SINUMERIK grounding scheme.

5. Encoder Configuration in the IndraDrive

On the IndraDrive side the encoder protocol at X4 (analog 1 V_PP) is configured using the IndraWorks commissioning tool. Set the following parameters:

• P-0-0074, Encoder type 1 = 0x10 (1 V_PP sin/cos, no serial protocol)
• P-0-0075, Encoder type 2 = 0x00 (none, emulated output disabled or repurposed)
• S-0-0117, Signal period of encoder 1 = line count of the IndraDyn H encoder (typically 2048 or 4096 lines/rev). Verify with the motor nameplate.
• P-0-0121, Emulated encoder output type = 0x01 (TTL RS-422, if the emulated output is to be used elsewhere; 0x00 if not)

IndraWorks will read back the calculated line count and indicate the input signal amplitude (target: 1.0 V_PP ± 10%). Values below 0.85 V_PP at the IndraDrive terminals usually indicate a long cable, a missing 120 Ω terminator at the receiver, or excessive common-mode noise picked up by the cable shield.

6. Encoder Configuration in SINUMERIK 840D (HLA Module Path)

The Siemens 840D provides two spindle feedback paths:

1. Standard path: SIMODRIVE 611D module with on-board encoder evaluation. The spindle encoder socket X411 is configured in spindle.cfg and the encoder type is set to 1 VPP through the Drive Settings mask (Startup → Commissioning → Drives → Spindle → Encoder Configuration).
2. HLA (Hydraulic Linear Analog) module path: Used when the spindle drive is not a Siemens drive and the controller interfaces via analog command. The HLA module is configured in the same commissioning tool but the encoder socket becomes the primary actual-value source. HLA accepts 1 V_PP, RS-422 TTL, or EnDat 2.1 depending on the module variant.

For this Rexroth retrofit the HLA module is the recommended configuration when the 611D slot is already occupied by axis drives. The encoder evaluation happens inside the HLA module and the result is fed to the same internal "actual value" bus the standard path uses.

The relevant machine data on the SINUMERIK side:

• MD30200 NUM_ENCS - number of encoders for the spindle (typically 1 or 2).
• MD30220 ENC_MSG_TIME - encoder message time, defaults to 0 for analog encoders.
• MD31000 ENC_IS_LINEAR = 0 (rotary encoder).
• MD31010 ENC_GRID_POINT_DIST = 20 µm (for 2048 line encoder with 1× interpolation; recalculated by the commissioning tool when the line count is entered).
• MD31020 ENC_RESOL = encoder pulses per revolution.
• MD31040 ENC_IS_DIRECT = 1 (direct mounted spindle encoder).

After loading these values, run the Reference point homing procedure (or the Spindle setpoint alignment when the encoder provides an index pulse) before commissioning rigid tapping or thread cutting.

7. Signal Integrity Considerations

7.1 Cable length budget

The Bosch Rexroth IndraDrive encoder interface tolerates up to 75 m of Heidenhain-specified cable at the rated 1 V_PP amplitude with the line count limited to 4096. The Siemens 611D module is specified to 30 m on the same cable type. The IBV 606 regenerates the signal, so the effective cable distance is reset at each output - the encoder-to-IBV link can be 75 m, and each IBV-to-receiver link can run the receiver's own maximum.

7.2 Shielding and grounding

Bond the encoder cable shield to the receiver (Siemens) end only. The encoder housing and the spindle body carry the grounding through their mechanical mounting. If the cable tray contains VFD power cables or DC bus cables from the IndraDrive, run the encoder cable on a separate tray or in a screened conduit with at least 200 mm separation. Avoid parallel runs longer than 5 m.

7.3 Power supply noise

The IBV 606 draws its operating power either from the encoder cable's 5 V line or from an external 5 V ±5% regulated supply. When using the encoder cable's 5 V, verify that the encoder can supply the additional 200 mA the IBV 606 draws on top of the encoder's own current. If the encoder cannot (very common with older IndraDyn H frameless motors), provide an external 5 V/1 A supply and tie it through a 10 Ω resistor to the encoder's +5 V line as a quieting filter.

8. Commissioning Step-by-Step

1. Power the cabinet down and verify zero voltage on the 611D DC bus and on the IndraDrive DC bus. Lock-out/tag-out the cabinet.
2. Mount the IBV 606 on a metal backplate inside the cabinet, within 1 m of one of the receivers to minimize cable length.
3. Wire the encoder input cable from the spindle to the IBV 606 input. Verify 5 V at pins 12 and 10 of the Heidenhain connector with a multimeter.
4. Wire output A (1 V_PP) to the IndraDrive encoder input. Wire output B (1 V_PP) through the 12-pin-to-17-pin adapter to X411 of the SIMODRIVE 611D (or to the HLA module).
5. Power the cabinet and check the IndraDrive Encoder 1 Status in IndraWorks. Confirm amplitude 0.95-1.05 V_PP and clean sine display.
6. On the 840D, run the Drive Commissioning sequence. Enter the encoder line count from the motor nameplate. Save the configuration.
7. Rotate the spindle by hand slowly and observe the actual speed in the 840D Axis/Spindle service screen. The reading should change smoothly and proportionally to rotation speed. Any flicker or dropout points to a wiring problem - typically a missed 120 Ω termination or a swapped A/B pair.
8. Run the spindle at 500 rpm, 1500 rpm, and maximum rated rpm. Confirm stable actual-speed display with no following-error alarms.
9. Enable rigid tapping (TAPPING) on a known thread and verify spindle/axis synchronization. Rigid tapping is the most demanding consumer of 1 V_PP encoder quality because it uses the encoder for closed-loop synchronization between axis and spindle.
10. Run an SPOS positioning command to a specific angle (e.g. SPOS=90°) and verify the spindle stops at the commanded angle within the configured tolerance (default ±1°).

9. Fault Matrix and Troubleshooting

10. Spindle Control Loop Architecture - What Closes Where

The IndraDrive closes its own torque and velocity loop against the encoder. The SINUMERIK 840D closes the position loop only when spindle positioning (SPOS) or rigid tapping is active. The encoder is the shared physical input; the IBV 606 makes that sharing possible without coupling the two control loops electrically.

11. Safety and Functional Compliance Notes

The IBV 606 is not a safety-rated component (no SIL/PL rating, no IEC 61800-5-2 safe-stop integration). When the machine is rated Category 3 or Performance Level d under ISO 13849-1, the spindle encoder feedback used by the 840D for actual-speed monitoring cannot be the same physical encoder used for safe-speed monitoring unless both paths are evaluated independently - in practice the safe-speed encoder is a separate hardware channel (e.g. a Heidenhain ECN 1325 on the motor end). Sharing a single 1 V_PP encoder through an IBV 606 is acceptable for non-safety functions only.

For compliance with EN 60204-1 and IEC 61800-1, ensure that the IBV 606 power supply and the encoder cable shield are bonded to the same protective-earth (PE) network as the cabinet, and that the cable routing respects the creepage and clearance distances specified in those standards for the cabinet's pollution degree and overvoltage category.

12. Sizing Example - Cable Length Budget

For a typical mid-size VMC retrofit with a frameless IndraDyn H spindle:

• Encoder mounted at the back of the spindle: cable length to cabinet = 8 m.
• IBV 606 mounted in cabinet 0.3 m from the SINUMERIK 611D slot.
• IndraDrive mounted in cabinet 1.5 m from IBV 606 (separate drive cabinet).

Run the encoder-to-IBV 606 cable at 8 m (well under the 75 m Heidenhain limit). Run IBV-to-IndraDrive at 1.5 m. Run IBV-to-SINUMERIK at 0.3 m. Total signal path budget consumed: 9.8 m. Headroom for future re-routing: 65 m on the encoder leg, ample.

The corresponding 5 V drop on the encoder cable at 8 m, with the encoder drawing 100 mA and the IBV 606 drawing 200 mA: voltage drop = 0.3 A × 0.7 Ω/m × 16 m (round trip) = 3.4 V. This exceeds the budget; the encoder's regulator cannot sustain a 5 V supply across this drop. The solution is to provide the IBV 606 with an external 5 V supply and let the encoder cable carry only the 100 mA encoder load. With only 100 mA load, the round-trip drop is 1.1 V - acceptable for a regulator with a 1.5 V dropout budget.