1. Encoder Identification and Order Number Structure
The Siemens 6FX2001-4SA10 is a hollow-shaft incremental encoder from the 1FT/6FX motor-feedback family, configured in the HTL (High Threshold Logic) push-pull 24 V DC variant. The encoder was originally designed as a position feedback device for SINAMICS S120 and SIMOTION motion control systems, but the open, well-documented pinout makes it equally applicable as a general-purpose HTL pulse source for any 24 V counter module, including the SIMATIC S7-1500 Technology Module (TM) Count 2x24V (order number 6FE7552-1AA00-0AB0).
The 6FX2001 order number follows Siemens' standard incremental encoder convention. The segment after the hyphen identifies the electrical interface:
| Segment | Value | Meaning |
|---|---|---|
| 6FX2001 | Series | Siemens incremental encoder, hollow/solid shaft, M23 12-pin |
| -2 | TTL 5 V | Single-ended TTL outputs, 5 V supply |
| -3 | TTL RS422 | Differential TTL outputs, 5 V supply |
| -4 | HTL 24 V | Push-pull 24 V outputs, 24 V supply (this part) |
| -5 | Sine 1 Vpp | Sinusoidal 1 Vpp outputs for high-resolution interpolation |
| S | Flange type | Synchro flange; C = clamp flange, E = blind hollow shaft |
| A | Shaft | Through-type hollow shaft |
| 10 | Resolution code | Refer to Siemens D21.4 catalog, page 12/50 for ppr value |
2. Electrical and Mechanical Specifications
| Parameter | Value | Notes |
|---|---|---|
| Supply voltage (Up) | 24 V DC (10 V to 30 V typical range, 24 V nominal) | Protected against reverse polarity |
| Current consumption | ~150 mA typical (no load) | Add cable length derating for long runs |
| Output level High | ≥ Up - 2.5 V (push-pull) | Drives RS422 receivers with pull-ups |
| Output level Low | ≤ 2.5 V | Sink/source capable |
| Output current per channel | 30 mA typical, 60 mA short-circuit peak | Per Siemens datasheet limit |
| Channels | A, /A, B, /B, R (zero), /R | Differential; A/B quadrature, R = reference mark |
| Max output frequency | 200 kHz (HTL variant -4) | Mechanical max rpm depends on ppr |
| Connector | M23, 12-pin, male on encoder body | Coupling: 6FX2003-0SA12 |
| Operating temperature | -20 °C to +85 °C (encoder body) | Cable derating applies separately |
| Protection class | IP65 (housing) when connector mated | Connector side is the IP weakness |
3. M23 12-Pin Connector Pinout (6FX2003-0SA12)
The encoder is terminated on a male M23 12-pin connector with a single locking screw coupling. The Siemens standard incremental HTL pin assignment is shown below. Pin numbering follows the M23 convention: viewing the male pins (encoder side), pins count clockwise starting at 1 next to the keyway.
| Pin | Signal | Function | Direction |
|---|---|---|---|
| 1 | Up | Encoder supply +24 V | Power in |
| 2 | 0V (M) | Encoder supply return | Power in |
| 3 | A | Incremental channel A (positive) | Output |
| 4 | /A (A*) | Incremental channel A inverted | Output |
| 5 | B | Incremental channel B (positive) | Output |
| 6 | /B (B*) | Incremental channel B inverted | Output |
| 7 | R (N) | Reference / zero mark (positive) | Output |
| 8 | /R (N*) | Reference / zero mark inverted | Output |
| 9 | Vacant | Reserved / unused | -- |
| 10 | Vacant | Reserved / unused | -- |
| 11 | Vacant | Reserved / unused | -- |
| 12 | Vacant (cable shield bonding point) | Use as shield bond per Siemens cable drawing | Shield |
4. Pre-Assembled Cable Selection: 6FX5002-2CA12
The 6FX5002-2CA12 is the Siemens catalogue cable for the 6FX2001-4 HTL incremental encoder family. It is supplied as a pre-assembled cable with an M23 12-pin female socket on the encoder end and an open (free) end on the controller end, which is the configuration required for termination to the S7-1500 TM Count 2x24V front connector.
Reference documents:
- Connection diagram (Siemens Industry Online Support, entry ID 109739295): 6FX5002-2CA12 cable drawing
- D21.4 catalog (entry ID 109747019): D21.4 cable and connector catalog
- Siemens connection diagram (entry ID 2103044): 6FX 2001-4 incremental encoder connection diagram
| Segment | Meaning |
|---|---|
| 6FX5002 | Siemens pre-assembled cable family for 6FX2001/6FX2002/6FX2003 |
| 2 | Basic version cable (non-drag chain, non-torsion) |
| C | Signal cable (not power) |
| A | Incremental encoder cable |
| 12 | M23 12-pin, free end, A-side prepared cable |
| -0AB0 | Length code (e.g. -1AB0, -2AB0, etc.; each AB0 = 10 m increment) |
5. 6FX5002-2CA12 Color Code
Siemens pre-assembled signal cables use a fixed wire color code that is documented in the cable drawing (entry ID 109739295). Use this table to map each M23 pin to a wire color on the free end that lands on the TM Count front connector.
| Pin (M23) | Signal | Wire Color (core) | Twist pair |
|---|---|---|---|
| 1 | +24 V (Up) | Red (RD) | Power pair |
| 2 | 0 V (M) | Blue (BU) | Power pair |
| 3 | A | Yellow (YE) | Pair 1 (A, /A) |
| 4 | /A | White (WH) | Pair 1 (A, /A) |
| 5 | B | Green (GN) | Pair 2 (B, /B) |
| 6 | /B | Gray (GY) | Pair 2 (B, /B) |
| 7 | R (zero mark) | Black (BK) | Pair 3 (R, /R) |
| 8 | /R | Violet (VT) | Pair 3 (R, /R) |
| 9-11 | Vacant | -- | Cut and isolate; do not connect to 0V or shield |
| 12 | Cable shield | Bare / drain wire | Bond to PE at controller end only |
6. S7-1500 TM Count 2x24V Module Overview
The TM Count 2x24V (6FE7552-1AA00-0AB0) is a technology module for the SIMATIC S7-1500 backplane that provides two independent 24 V HTL/TTL counter channels. Each channel can evaluate an incremental encoder with A, B, and optional zero (Z) mark. Relevant electrical characteristics for the 6FX2001-4 hookup:
| Parameter | Value |
|---|---|
| Encoder supply output | 24 V nominal, 1.0 A per channel, 2.0 A per module |
| Input voltage range | 0 V to 30 V (24 V logic family) |
| Switching threshold High | ≥ 11 V (HTL mode) |
| Switching threshold Low | ≤ 5 V (HTL mode) |
| Max input frequency | 200 kHz per channel (HTL, differential) |
| Supported signal modes | Single-ended HTL, differential HTL, single-ended 24 V TTL |
| Counting range | -2^31 to +2^31 - 1 (32-bit signed) |
| Front connector | 40-pin push-in / screw, 0.5 mm² to 1.5 mm² |
The module can source the encoder's 24 V supply directly from its front connector; an external 24 V supply is normally not needed unless the encoder's 150 mA draw plus cable losses exceeds the 1.0 A per-channel limit. For cable runs under 50 m, the internal supply is sufficient.
7. TM Count 2x24V Front Connector Pinout
The 40-pin front connector is split into two channel groups. Only the pins needed for an incremental HTL encoder are shown.
| Pin | Channel | Function |
|---|---|---|
| 1 | Ch0 | A0 (track A, positive) |
| 2 | Ch0 | /A0 (track A, inverted) |
| 3 | Ch0 | B0 (track B, positive) |
| 4 | Ch0 | /B0 (track B, inverted) |
| 5 | Ch0 | Z0 (zero mark, positive) |
| 6 | Ch0 | /Z0 (zero mark, inverted) |
| 7 | Ch0 | 24 V encoder supply output |
| 8 | Ch0 | 0 V encoder supply return |
| 9 | Ch1 | A1 |
| 10 | Ch1 | /A1 |
| 11 | Ch1 | B1 |
| 12 | Ch1 | /B1 |
| 13 | Ch1 | Z1 |
| 14 | Ch1 | /Z1 |
| 15 | Ch1 | 24 V encoder supply output |
| 16 | Ch1 | 0 V encoder supply return |
| 1L+ | -- | 24 V module power supply |
| 1M, 2M | -- | 24 V module power return |
| FE | -- | Functional earth (shield bonding rail) |
8. Wiring Procedure: 6FX2001-4SA10 to TM Count 2x24V
- Verify you have the cable 6FX5002-2CA12 (free end, M23 12-pin) of the correct length. The 6FX2001-4SA10 is the encoder; the cable is separate.
- Power down the S7-1500 and the TM Count module before terminating the front connector.
- Route the cable to the encoder; install the M23 12-pin female socket onto the encoder's M23 connector. Tighten the locking screw to the M23 manufacturer's specified torque (typically 0.5-0.6 N·m) to maintain IP65.
- Strip approximately 50 mm of the cable jacket at the controller end. Be careful not to cut into the shield braid.
- Fold the shield braid back over the jacket and secure it with a shield clamp on the TM Count front connector's FE terminal or the dedicated cable strain relief. Bond the shield to FE on the controller end only; the encoder body is the far-end ground reference through the M23 connector shell.
- Strip each signal wire approximately 8 mm. Use ferrules (Weidmüller / Phoenix) sized for the 0.34 mm² conductors.
- Terminate per Table 8. Maintain twist pair geometry on each pair (A//A, B//B, R//R); untwist no more than 25 mm per pair.
- Cap the vacant wires (pins 9, 10, 11) individually with wire end caps. Do not connect them to 0V or shield.
- Seat the front connector on the TM Count module; tighten the locking screw.
- Apply 24 V module power. Check the channel status LED on the TM Count module for the channel you wired.
| Encoder Pin (M23) | Wire Color | TM Count Terminal | Notes |
|---|---|---|---|
| 1 (+24 V) | Red | 7 (24 V enc supply Ch0) | From internal supply; verify ≤ 1.0 A |
| 2 (0 V) | Blue | 8 (0 V enc supply Ch0) | Same 0V used for power return and signal reference |
| 3 (A) | Yellow | 1 (A0) | -- |
| 4 (/A) | White | 2 (/A0) | Required for differential; do not leave floating |
| 5 (B) | Green | 3 (B0) | -- |
| 6 (/B) | Gray | 4 (/B0) | Required for differential |
| 7 (R) | Black | 5 (Z0) | Only if zero mark evaluation needed |
| 8 (/R) | Violet | 6 (/Z0) | Required for differential |
| 9, 10, 11 | -- | Cut and cap | Do not connect |
| 12 (shield) | Bare / drain | FE terminal | Bond to controller PE rail |
9. TIA Portal Configuration
- In the TIA Portal device view, add the TM Count 2x24V (6FE7552-1AA00-0AB0) to the S7-1500 station. Confirm the firmware version is compatible with the configured TIA Portal version (see TIA Portal release notes for the exact compatibility matrix; the module has been supported since TIA Portal V14 SP1).
- Open the module's properties and select "Incremental encoder" as the operating mode for channel 0.
- Set the signal evaluation to "Differential 24 V (HTL)" if both /A and /B are wired, or "Single-ended 24 V (HTL)" if only the non-inverted tracks are wired (not recommended for cable runs over 10 m).
- Set the count direction per encoder rotation. For a clockwise rotation looking at the encoder shaft, A leads B; for counter-clockwise, B leads A. Most S7-1500 applications invert the count direction in software by setting the "Invert direction" checkbox rather than swapping A and B wires.
- Set the encoder pulses per revolution (ppr) per the encoder's data plate. The 6FX2001-4SA10 ppr value is documented in the D21.4 catalog at page 12/50.
- Enable the zero mark (Z) evaluation if reference-mark-based homing is required. Select the gating mode: "Disable zero mark" / "Use zero mark once" / "Use zero mark continuously."
- Enable hardware interrupts for zero mark events if the program needs a hardware-based reference trigger.
- Map the I/O addresses of the TM Count into the process image. The most useful tags are the count value (DWord), the zero-mark latch (DWord), the direction status (Bool), and the hardware gate status (Bool).
- Compile and download the configuration. On the first download, the TM Count module performs a self-test; both channel status LEDs should turn solid green within 3 s.
10. Verification Procedure
- Power check: With the encoder stationary and the M23 connector mated, measure the voltage between M23 pin 1 and pin 2. Expect +24 V nominal (range: 21.6 V to 26.4 V at the encoder end, accounting for cable drop).
- Current check: Measure the encoder current on the +24 V wire. Expect 100-200 mA steady-state for the 6FX2001-4 family. Higher values indicate a shorted cable or a damaged encoder.
- Signal presence: Use an oscilloscope on M23 pins 3 and 5 (A and B). Slowly rotate the encoder shaft by hand. A and B should each produce a 50% duty square wave, 90° out of phase. Frequency in Hz ≈ (shaft rpm / 60) × ppr.
- Differential integrity: Verify /A is the logical inverse of A (similarly for /B and /R). Floating inverted inputs are the most common cause of apparent "missing counts" at low speeds.
- Zero mark: Rotate the shaft through one full revolution. One positive-going R pulse (and one /R pulse) per revolution. If using zero-mark homing, the TM Count latch register should update exactly once per revolution.
- Software sanity: In the S7-1500 user program, write a small counter monitor that displays the raw count value and the direction bit. Hand-rotate the shaft exactly 10 turns; the count should change by ± (10 × ppr) with no drift on each subsequent test.
- Error counters: Check the diagnostic buffer of the TM Count for the channel. A clean channel reports "OK" or no diagnostic entries. The error codes that appear commonly in the buffer are listed in the troubleshooting matrix below.
11. Troubleshooting Matrix
| Symptom | Likely Cause | Action |
|---|---|---|
| Channel status LED off; count does not update | No 24 V to encoder (cable open, M23 not fully mated, or front connector loose) | Verify +24 V at M23 pin 1; reseat front connector; verify the encoder's supply is enabled in TIA Portal |
| Count increments but is noisy (drifts, has jitter) | Floating /A or /B input, or shield not bonded to FE | Wire both /A and /B; bond cable shield to FE at the controller end |
| Count direction wrong | A and B swapped, or wiring reversal | Use the TM Count "Invert direction" parameter, or swap A and B at the front connector |
| Zero mark never detected | Z and /Z not wired; or the encoder type does not produce a /R output for the variant in use | Verify pins 7 and 8 are connected; check the ppr data plate for "N" or "R" mark specification |
| Diagnostic buffer entry: "Wire break" | Open circuit on A, B, or Z; or shield shorted to conductor | Continuity-check each wire end-to-end; inspect cable for insulation damage |
| Diagnostic buffer entry: "Sensor supply overload" | Total encoder current > 1.0 A (per channel), or short on 24 V output pin | Check encoder current; if > 1.0 A, switch to external 24 V supply |
| Counts missing at high rpm | Input frequency exceeds 200 kHz, or excessive cable capacitance on long runs | Reduce rpm; check max rpm = 60 × 200,000 / ppr; shorten cable or use 5 V TTL encoder (6FX2001-3) for long runs |
| Count value wraps around unexpectedly | Counter overflow at 32-bit signed boundary | Use the LOAD_VALUE input to preset at a known position, or add range-check logic in user program |
12. Compatibility Notes with the S7-1500 Family
The 6FX2001-4SA10 is mechanically and electrically compatible with the following SIMATIC S7-1500 modules:
- TM Count 2x24V (6FE7552-1AA00-0AB0): direct support, no external 24 V supply needed for cable runs < 50 m.
- TM PosInput 2 (6ES7553-1AA00-0AB0): supported but the TM PosInput is generally used with SSI/analog encoders. The TM PosInput can read HTL on its DI inputs, but the TM Count is the preferred module for HTL incremental work.
- ET 200MP TM Count 2x24V: identical pinout and electrical behavior, can be mounted remotely and wired through PROFINET to the S7-1500 CPU.
For older S7-300/S7-400 systems, the FM 350-1 counter module (6ES7350-1AH03-0AE0) and FM 350-2 (6ES7350-2AH01-0AE0) accept HTL 24 V encoders on their isolated inputs. The pinout, however, is on a 40-pin front connector with a different terminal layout; refer to the FM 350 manual for the wire-by-wire map.
Can the Siemens 6FX2001-4SA10 be used with the S7-1500 TM Count 2x24V?
Yes. The 6FX2001-4 is a 24 V HTL incremental encoder, and the TM Count 2x24V (6FE7552-1AA00-0AB0) accepts HTL push-pull inputs up to 200 kHz. Use the 6FX5002-2CA12 pre-assembled cable and wire the free end to the TM Count front connector using the pin-to-color map in Table 5 and Table 8.
Is the 6FX2003-0SA12 the encoder itself?
No. The 6FX2003-0SA12 is a 12-pin M23 connector kit (coupling) for cable termination, not an encoder. The encoder is the 6FX2001-4SA10. Use the 6FX2003-0SA12 only if you are building a custom cable; otherwise prefer the pre-assembled 6FX5002-2CA12.
Do I have to wire the inverted signals (/A, /B, /R)?
For runs under 10 m in benign electrical environments, single-ended HTL wiring (A and B only) will work. For longer runs, or in any cabinet with VFDs or contactors, wire all three differential pairs (/A, /B, /R). Floating inverted inputs cause count noise and are the most common source of "random count drift" complaints on field service calls.
Where is the official 6FX2001-4 wiring diagram?
Siemens publishes the connection diagram in Industry Online Support under entry ID 2103044. The D21.4 cable catalog (entry ID 109747019) and the 6FX5002-2CA12 cable drawing (entry ID 109739295) cover the pinout and cable color code respectively. The encoder data sheet itself intentionally omits the wiring diagram and refers back to these documents.
What is the maximum cable length between the 6FX2001-4SA10 and the S7-1500 TM Count 2x24V?
Siemens rates the 6FX5002-2CA12 cable up to 100 m for HTL operation, with the limitation being cable capacitance (typically ≤ 120 pF/m) and the resulting RC degradation of the square-wave edges. For runs over 50 m, switch to the 5 V TTL variant (6FX2001-3) and a corresponding TTL-capable counter module, or insert a line driver on long HTL runs.