Wiring Siemens 6ES7134-6GF00-0AA1 AI 8xI for 4-Wire 4-20mA

Overview

The SIMATIC ET 200SP analog input module AI 8xI 2-/4-wire BA (article number 6ES7134-6GF00-0AA1) is an 8-channel, 16-bit analog input rated for 4..20 mA current loops. It supports both 2-wire (loop-powered) and 4-wire (externally powered) transducers and ships with integrated short-circuit, reverse-polarity, and wire-break diagnostics. The module is deployed on an ET 200SP station (here, IM 6ES7155-6AU01-0CN0) and is configured in TIA Portal under an S7-1500 controller such as the CPU 1511C-1PN.

This reference documents the correct 4-wire 4..20 mA wiring scheme, clarifies the role of the module's Uv sensor supply, explains why the input word can latch at 32000 when wiring is wrong, and walks through the resolution verified on an ABB ACS560 drive analog output reference.

Module Identification & Specifications

Terminal Layout & Pin Assignment

The base unit used with the 6ES7134-6GF00-0AA1 exposes 16 push-in or screw terminals across two rows. Channel assignments are numbered 0..7; channel-specific terminals use the pattern I+ (input positive) and I.A (input analog ground, internally tied to the module's M reference).

2-Wire vs 4-Wire Transducer Theory

The distinction is in how the transducer receives its operating power:

• 2-wire (loop-powered): The transducer draws its operating current from the same pair that carries the 4..20 mA signal. By Kirchhoff's current law the loop current is the only path, so the signal floor is non-zero (4 mA) and the engineering zero is at 4 mA. The module's internal Uv supply feeds this kind of sensor directly.
• 4-wire (separately powered): Two wires carry the regulated DC supply from an external source (often the field instrument's own PSU or a discrete MCB-fed 24 V), and two wires carry the analog signal back to the input. Signal and supply are galvanically independent. This category includes most frequency inverter analog outputs such as the ABB ACS560 AO1/AO2 terminals.

For 4-wire devices, the module must not inject 24 V on its Uv rail into the signal loop, because the transducer already sources its own power. Uv becomes a no-connect or is left for the 2-wire channels.

Uv Supply Characteristics

Uv on the 6ES7134-6GF00-0AA1 is a current-regulated 24 V DC rail. It is dimensioned for the small standing current of 2-wire 4..20 mA loops (≈ 4 mA minimum per channel). It is not a power output intended to feed 4-wire transmitters, drive contactors, or supply sensors that demand more than a few milliamps.

When a 4-wire transducer is wired but the module's Uv is also left connected to that sensor's supply input, two sources end up in parallel, which can cause:

• Ground-loop currents that lift the low-side reference above 0 V at the module's A terminal.
• Back-feeding of the field PSU through Uv, raising the channel's effective input above the legitimate 20 mA saturation.
• Saturated A/D conversion reading > 27648 in the process image, which in TIA Portal is visible as the value 32000 when the loop drives the front end past its compliance range.

Correct 4-Wire 4..20 mA Wiring Procedure

Use the diagram and steps below when the field sensor is an externally powered 4-wire transmitter (e.g., ACS560 AO output, level transmitter, pressure transmitter).

Step-by-Step

1. Power down the ET 200SP station and the field device. Lock and tag the 24 V supply.
2. Verify the module article number printed on the front: 6ES7134-6GF00-0AA1. Mixing up the BA with an ST variant changes pinout and configuration.
3. Select the correct measurement type in TIA Portal: Device configuration → AI 8xI 2-/4-wire BA → Channel 0 → Measurement type = Current (4..20 mA) → Wiring = 4-wire. The Wiring dropdown is what activates the correct scaling and disables Uv feed-through for that channel.
4. Run the signal cable from the transmitter's OUT (+) terminal to the module's I0+ terminal on the BaseUnit.
5. Run the transmitter's RET (-) (signal return) to the module's I0A terminal on the same BaseUnit. I0A is internally bonded to the channel's analog reference; this is the only low-side path that completes the current loop into the A/D front end.
6. Provide the transmitter's 24 V supply from a separate, regulated MCB-fed source. Connect +24 V and 0 V to the transmitter's power terminals. Tie the 0 V of this supply to the same protective earth and to the ET 200SP station ground.
7. Leave Uv unused for this channel. Do not jumper Uv to the +24 V field wire. If Uv must remain energized (because other channels on the same module are 2-wire), be certain its wiring does not touch the 4-wire sensor's supply input.
8. Tighten screw terminals to the manufacturer-published torque (≈ 0.5 N·m for the BU15-P16+A0/+A1 BaseUnits) and re-energize in this order: field supply → ET 200SP interface module → AI module → controller.

Why the Process Image Latches at 32000

The S7-1500 analog-input process image interprets the raw A/D count using the IEC 61131-9 normalized scale:

A reading of 32000 in the input word (e.g., %IW64) typically means the AI is reading just under the overflow threshold - the loop is being driven by a parallel voltage source or by back-feed through Uv. The most common root causes observed in the field:

1. The transmitter's signal return and the module's I.A are bonded at the transmitter and at the cabinet chassis, creating a ground loop that lifts the module's reference above the loop's return.
2. Uv has been wired in parallel with the field 24 V, so two regulators fight each other and the loop voltage climbs past 22.8 mA equivalent.
3. The transmitter is configured for 0..20 mA output but the module is configured for 4..20 mA, so the bottom of the range reads -32768 and the top reads > 27648.
4. The AI channel was set to Voltage by mistake and is being fed from a 4..20 mA source across its input impedance, pushing the input amplifier into saturation.

Resolution Procedure for the 32000 Fault

1. In TIA Portal, open Devices & Networks → ET 200SP station → AI 8xI 2-/4-wire BA → Properties → Module parameters → Channel 0. Confirm:

• Measurement type: Current
• Current range: 4..20 mA
• Wiring: 4-wire (not 2-wire)
• Diagnostics: Overflow, wire break, short to ground enabled

2. Re-wire using the diagram in the previous section. Make sure Uv (terminals 9..16) is not bonded to the sensor's supply.
3. Disconnect the transmitter's analog return from any chassis ground at the cabinet entry plate; the only return path should be the wire into I0A.
4. Compile and download the hardware configuration. Online, observe %IW64 (or the assigned channel input word for the relevant slot). A healthy signal at 12 mA should now read ≈ 13824.
5. If the AI module and the 4-channel module (e.g., 6ES7134-6JD00-0CA1) on the same station are both reading correctly but the 8-channel BA is not, the difference is almost always parameter configuration or wiring convention - never assume the BA is defective.

Commissioning & Verification in TIA Portal

Once wired, perform the following live checks before placing the loop in automatic control:

1. Reference check (4 mA): Force the transmitter output to its minimum. Expect IW = 0 ± 16 counts.
2. Span check (20 mA): Force the transmitter output to maximum. Expect IW = 27648 ± 16 counts.
3. Linearity check (12 mA): Mid-scale force should read ≈ 13824.
4. Diagnostic test: Open the signal wire at the transmitter end (with the loop powered). The module should report wire break (event ID 0x0311 in the diagnostics buffer) and the channel value should be -32768.
5. Ground-loop sniff: Use a clamp-on milliamp meter on the signal return wire; if it does not match the milliamp reading on the signal+ wire, a parallel path exists.

Troubleshooting Matrix

Specific Notes for the ABB ACS560 VFD Hookup

When sourcing a 4..20 mA reference from an ABB ACS560:

• Use terminals AO1+ (1) and AO1- (2) for the analog output. The drive sources the loop power internally (it acts as a 4-wire transmitter from the PLC's perspective).
• Configure parameter group 13 on the ACS560 (analog outputs): select signal source (e.g., parameter 01.06 Motor speed), scale the output range with parameters 13.15..13.20, and set Output signal scaling to 4..20 mA.
• Wire AO1+ to the ET 200SP AI module's I0+ terminal and AO1- to the module's I0A terminal. Do not bring drive ground to the module's M; use only the AO1- return.
• If the drive and the ET 200SP share a common cabinet 0 V bus, that bond is sufficient; do not add a second bond through the AO cable shield.

Adjacent Module Comparison

FAQ