Wiring 6ES7134-6GF00-0AA1 ET 200SP AI 8xI to 4-Wire 4-20mA Inputs

1. Module Identification and Key Specifications

The 6ES7134-6GF00-0AA1 is the SIMATIC ET 200SP analog input module AI 8xI 2-/4-wire HS. It accepts eight current inputs from either 2-wire (loop-powered) or 4-wire (externally powered) field transmitters, occupies a single slot in an ET 200SP station, and is identified as a high-speed (HS) variant. The "HS" suffix is the critical differentiator on this part number; the 6ES7134-6GF00-0AA1 must not be confused with the standard AI 8xI 2-/4-wire (6ES7134-6GD00-0BA1) or the AI 2xU/I 2-/4-wire HF (6ES7134-6HB00-0CA1), each of which has a different channel count, resolution class, and update time.

Key electrical and functional parameters of the 6ES7134-6GF00-0AA1:

The HS module achieves its high update rate by sampling channels in parallel against a small integration window. For 4-wire (active) transmitters, the module does not source loop power; it only senses. This is the source of the most common wiring confusion in the field, because the same module can also be configured for 2-wire transmitters where it does source 24 V through the AUX terminals.

2. 2-Wire vs 4-Wire Transmitter Fundamentals

Understanding the distinction is essential before choosing a wiring scheme.

For the source's specific transmitter — the Endress+Hauser Liquiline CM44x with eight current output modules — every output is described by the manufacturer as "active" and "potentially isolated from one another and from the sensor circuits". This is a critical fact because it dictates the ground loop analysis in Section 7.

3. ET 200SP BaseUnit Terminal Layout

The AI 8xI 2-/4-wire HS uses a 16-terminal BaseUnit (BU type A0 or A1). Terminal assignments for one channel pair (Channel 0 / Channel 1) are shown below; the remaining six channels follow the same pattern (Ch2/3, Ch4/5, Ch6/7) on terminal rows 5–8 of the BaseUnit.

The AUX terminals (A0 through A10 on the BaseUnit's printing) are the 24 V sensor supply rails. They are not required when connecting a 4-wire active transmitter, because that transmitter draws its operating current from its own supply. They are required when connecting a 2-wire (loop-powered) transmitter.

4. Prerequisites

1. Hardware inventory
   • One ET 200SP station with an IM 155-6 (any variant), one BU15-P16+A0+... BaseUnit, and one 6ES7134-6GF00-0AA1 module.
   • Eight (or fewer) Endress+Hauser CM44x current output channels, or equivalent 4-wire 0/4–20 mA transmitters.
   • 24 V DC control power supply for the ET 200SP module supply (SELV/PELV, ≥ 1 A available per module slot).
   • For 120 V AC powered transmitters: a separate 24 V DC PSU is not needed for the AI module side; the transmitter carries its own mains supply.
   • Shielded twisted-pair instrumentation cable, e.g., Belden 8760, Alpha 2466C, or Lapp Ölflex® Classic 110 CY.
2. Software
   • Siemens TIA Portal V15.1 or later (V17 or newer recommended for the latest GSD/HSP for ET 200SP).
   • ET 200SP HSP (Hardware Support Package) installed so the AI 8xI 2-/4-wire HS appears in the device catalog.
   • CM44x TI00444C technical information document for output compliance voltage.
3. Documentation
   • ET 200SP Manual Collection, in particular the AI 2xU/I 2-/4-wire HF wiring and block diagram page, which is structurally identical to the AI 8xI for 4-wire applications: SIMATIC ET 200SP — Wiring and block diagram (AI 2xU/I 2-/4-wire HF).
   • Endress+Hauser CM44x Technical Information TI00444CEN, page 20 (output specs): TI00444CEN/07/EN/14.19 (Liquiline CM44x).
4. Safety
   • De-energize the ET 200SP power supply and the transmitter mains before opening the cabinet.
   • Confirm that the transmitter's output is "active" (self-powered). If it is "passive" (loop-powered), you must wire to the AUX terminals instead — see Section 12 troubleshooting matrix.

5. Step-by-Step Wiring Procedure for a 4-Wire Active Transmitter

The following procedure wires a single 4-wire, 120 V AC powered, 4–20 mA active transmitter to channel 0 of the AI 8xI 2-/4-wire HS module. Repeat steps 1–5 for each additional channel.

1. Identify the four conductors in the field cable. Label them unambiguously: L (line), N (neutral), SIG+ (current output +), and SIG− (current output − / return). Most CM44x output channels expose these as a removable terminal block; consult the device's wiring diagram sticker.
2. Power the transmitter: connect L and N to the 120 V AC mains branch circuit. Provide a local disconnect and overcurrent protection. The transmitter enclosure should be grounded per local code (PE).
3. Land the signal pair on the BaseUnit:
   • Transmitter SIG+ → BaseUnit terminal In0+ (channel 0 input positive).
   • Transmitter SIG− → BaseUnit terminal 0V (M0) (channel 0 signal return / module ground reference).
4. Do not connect the AUX0+/AUX0− terminals on this channel. Because the transmitter is active, no sensor supply is needed. Leaving AUX unused is correct for 4-wire active devices.
5. Terminate the cable shield at the BaseUnit's FE terminal (shield clamp). Strip only as much jacket as needed so the shield does not extend past the clamp; the goal is a low-impedance path to the cabinet ground bar.
6. Verify polarity and short-circuit protection: with a multimeter in current mode, measure between In0+ and 0V (M0). You should read between 4 and 20 mA corresponding to the live process variable; 0 mA indicates open loop, > 25 mA indicates a wiring fault.

6. CM44x Integration

The Endress+Hauser Liquiline CM44x is a multi-parameter transmitter that can host up to eight current output modules (e.g., 2 x BASE2-E modules with 4 outputs each, or similar configurations). Per TI00444CEN, page 20, each output is specified as:

• Range: 0/4 to 20 mA
• Type: active (the module provides loop power internally)
• Isolation: potentially isolated from one another and from the sensor circuits
• Maximum load: typically 500 Ω (verify against the actual CM44x variant)

The "potentially isolated" wording is significant. It means E+H designs the outputs so they can be channel-to-channel isolated, but the final isolation state depends on the wiring configuration chosen in the field. If the negative leg of every output is tied to the same 0 V (M) terminal on the AI module, the channels share a common reference and isolation is defeated. Conversely, if each SIG− conductor lands on its own 0 V (Mx) terminal and no other connection joins them externally, channel-to-channel isolation is preserved.

Best practice for the AI 8xI 2-/4-wire HS when interfacing all eight CM44x outputs:

1. Land each transmitter's SIG− on a distinct signal return terminal. On the BaseUnit these are 0V M0, M1, M2, … M7 (one per channel). Do not jumper them together outside the module.
2. Maintain twisted-pair discipline (SIG+ twisted with SIG−) all the way to the BaseUnit; do not run individual conductors in separate conduits.
3. Verify ground potential between the CM44x PE bar and the cabinet ground bar with a voltmeter; the difference should be < 1 V AC and < 0.5 V DC under normal conditions. Persistent readings in the volts indicate a need for an isolation solution (Section 8).

7. Ground Loop Analysis and Mitigation

A ground loop exists whenever the transmitter's signal return and the AI module's signal return are referenced to ground at two different points that are not at the same potential. The current that circulates through the resulting loop adds an offset to the measured signal. The symptom is a stable but wrong reading — often a few hundred microamps — that does not match the calibrated 4 mA or 20 mA points.

Three conditions that together create a ground loop on the 6ES7134-6GF00-0AA1:

1. The transmitter's SIG− terminal is tied to its own enclosure ground (PE) at the field end.
2. The AI module's 0 V (M) terminal is tied to the cabinet's protective earth at the PLC end.
3. The two earth points are bonded only back at the source transformer, so the field PE and the cabinet PE are at slightly different potentials, especially when large 3-phase loads are running.

Symptoms in order of severity:

• Small positive offset (1–3 % of span) on all channels
• Random channel-to-channel cross-talk where adjusting one channel's zero shifts others
• Readings pinned at +20.5 mA (overflow) or −20.5 mA (underflow) with diagnostic LEDs solid red
• Module DIAG LED flashing red, with diagnostic buffer entry "Wire break" or "Overflow" even though the loop is intact

8. Signal Isolator Selection

If a ground loop is confirmed, or if the application is in a particularly noisy plant (VFDs, large motors, MIG welders), install a 4–20 mA signal isolator in the field cable run between the CM44x output and the AI channel. The isolator breaks the galvanic path between the two grounds while passing the 4–20 mA signal transparently.

Suitable isolator families (all DIN-rail mount, 24 V DC powered, loop- or supply-powered variants):

For the CM44x use case, prefer a Hart-transparent isolator (e.g., KCD2-SCD-1, Phoenix MINI MCR-2-UI-UI-PT). The CM44x uses HART for asset management and remote calibration; a non-Hart-transparent isolator will block HART communication and prevent re-ranging from the PLC or from Emerson AMS / Endress+Hauser FieldCare.

Insertion point: as close as practical to the CM44x terminals, inside the analyzer cabinet. The isolator's input side then sees the CM44x as a current source; the isolator's output side becomes a fresh, isolated current source for the AI channel.

9. TIA Portal Configuration

1. Add the module to the device configuration: drag the AI 8xI 2-/4-wire HS from the catalog to the ET 200SP slot. If the module does not appear, install the latest ET 200SP HSP via Options → Support Packages and restart TIA Portal.
2. Open the module properties and navigate to Analog inputs → Channels.
3. Set the measurement type for each channel to Current (4-wire). The dropdown presents Current (2-wire) and Current (4-wire); the 4-wire setting is the one that disables the AUX sensor supply on that channel group.
4. Select the input range: 4 to 20 mA for standard HART-bearing transmitters, 0 to 20 mA for legacy devices, or ±20 mA for bipolar applications.
5. Enable diagnostics: under Diagnostics, enable Wire break, Overflow, and Underflow. For 4–20 mA with HART, consider disabling wire break at low end only if your plant's installation routinely has currents below 3.5 mA (otherwise noise spikes will trigger spurious wire-break events).
6. Configure smoothing if needed: in the Inputs tab, set the integration time. The HS module supports values such as 100 µs, 1 ms, 10 ms, and 20 ms. For the CM44x, 10 ms or 20 ms is recommended; the analyzer's own response time is on the order of seconds, so faster integration just adds noise.
7. Assign the IO addresses: by default the module occupies input bytes 0–15 (8 channels × 2 bytes). Note the start address for the PLC tag table.
8. Compile and download the hardware configuration to the ET 200SP IM and the CPU 1510S. After a STOP→RUN transition, the DIAG LED on the AI module should be steady green.

Sample TIA Portal data block snippet for a 4–20 mA engineering conversion (SCL, for an ET 200SP AI 8xI at address IW256):

// Raw input from channel 0 of the AI 8xI 2-/4-wire HS
#iRaw := "AI_Ch0".%IW;          // 16-bit signed integer
#rPercent := INT_TO_REAL(#iRaw) / 27648.0;
#rMilliamp := 4.0 + 16.0 * #rPercent;
#rEngineering := (#iRaw - 0) / (27648.0 - 0) * (#rEU_High - #rEU_Low) + #rEU_Low;

10. Verification and Commissioning

1. Visual inspection: confirm shield is clamped at the BaseUnit FE terminal, not at the field transmitter; shield should be one-ended to avoid ground loops through the shield itself.
2. Loop power check: with the transmitter powered and the field cable connected, measure the DC voltage between In0+ and 0V (M0). For a CM44x active output the voltage should be in the 12–24 V range depending on load. Zero volts indicate a wiring fault.
3. Current check: break the SIG+ conductor and insert a multimeter in series. Apply a known process condition (e.g., use a CM44x simulation routine) and verify that the measured current matches the expected mA value within 0.1 %.
4. Module-level diagnostics: in TIA Portal, go online and open Online & Diagnostics → Diagnostics for the AI module. All enabled diagnostic categories should report OK.
5. Channel-level value test: force each channel to 4.000 mA, 12.000 mA, and 20.000 mA in turn, and verify the scaled engineering value matches within the configured tolerance.
6. Ground loop stress test: with all eight channels live, briefly start the largest 3-phase load in the cabinet and observe channel readings for drift. Drift > 0.5 % of span during the transient is a strong indicator that an isolator is required.

11. Troubleshooting Matrix

12. Frequently Asked Questions