LOGO! 8.3 AM2 Expansion: AI Address Mapping for 4-20mA Sensors

1. Overview: LOGO! 8.3 Modular I/O Architecture

Siemens LOGO! 8.3 is a modular logic relay that combines a programmable controller, operator interface, and I/O in a single 72 mm-wide housing. The 12/24 V DC base module (catalog suffix 2CC) supports four on-board 0-10 V analog inputs shared with digital inputs I1, I2, I7, and I8. With up to eight expansion modules on the right side, the system scales to 24 digital inputs, 20 digital outputs, and 8 analog inputs. A frequent configuration issue is the apparent mismatch between the physical terminal label (I1 on an AM2 expansion) and the logical address visible in the program (AI1, AI3, or AI5). The address depends on how many analog input slots are reserved for the base module in LOGO! Soft Comfort's I/O settings.

This article documents the addressing rule for a configuration consisting of:

• Base module 6ED1052-2CC08-0BA0 (LOGO! 8.3 12/24 RCEo, relay outputs, Ethernet)
• Two LOGO! AM2 expansion modules 6ED1055-1MA00-0BA2 (2 AI each, 0-10 V or 0-20 mA, jumper-selectable per channel)
• A 4-20 mA two-wire sensor wired to the I1 terminal of the first AM2

Target firmware is LOGO! 8.3 system firmware 1.82.x or later, paired with LOGO! Soft Comfort V8.3 or later. Earlier 0BA7 and 0BA8 base units follow the same addressing rule but use a different Tools menu path. The full system manual is available on the Siemens Industry Online Support portal under entry ID 109751049.

2. Topology of the Two-AM2 Configuration

The figure shows the bus layout, terminal labels, and resulting AI addresses when the default four-slot reservation is kept on the base module.

3. Base Module 6ED1052-2CC08-0BA0: Hardware Map

Catalog number 6ED1052-2CC08-0BA0 designates the LOGO! 8.3 12/24 RCEo variant. The suffix is decoded as follows:

The 12/24 V DC power supply allows the four on-board analog inputs to operate as 0-10 V inputs without an external transducer. The fixed digital-to-analog mapping is:

The base module also provides 4 relay outputs Q1-Q4 (normally open, 10 A / 250 V AC / 30 V DC) and a 10/100 Mbit/s Ethernet port supporting S7 communication, Modbus TCP server, and the LOGO! Web Editor. The 0-10 V analog inputs share the physical terminal with the digital input, so a 24 V digital input on I1 and a 0-10 V analog input on I1 cannot coexist. By default, LOGO! Soft Comfort reserves all four AI slots (AI1-AI4) for the base module regardless of physical wiring.

4. AM2 Expansion Module 6ED1055-1MA00-0BA2: Specifications

For 4-20 mA sensors, the AM2 channel must be set to current mode (0-20 mA) by moving the on-board jumper from "U" to "I" for that channel. The 0-1000 raw value is then mapped over the 0-20 mA span: 0 = 0 mA and 1000 = 20 mA. The application program performs live-zero compensation: subtract 200 (the raw equivalent of 4 mA) and scale to engineering units.

5. 4-20 mA Sensor Wiring

For a two-wire 4-20 mA sensor powered from the cabinet 24 V DC rail, use the following termination:

1. Connect the +24 V DC rail to the sensor's red wire (or terminal +).
2. Connect the sensor's black wire (terminal -) to AM2 terminal I1+.
3. Bridge AM2 terminal I1- to the 24 V DC common (0 V) at the AM2 terminal block.
4. Set the AM2 channel-1 jumper to the "I" position. The jumper is on the PCB, accessible after removing the terminal cover.
5. Use shielded twisted pair; ground the shield at the cabinet entry gland only. Do not ground the shield at the sensor end to avoid ground loops.

Wiring schematic (text representation):

  Cabinet +24V DC
        |
        |  (fused, 100 mA)
        +---------> [Sensor +V]
                          |
                       [Sensor]
                          |
                       [Sensor -V]
                          |
                          +---------> AM2 I1+   (terminal block)
                                           |
                                       250 Ω
                                       (built in)
                                           |
                                       AM2 I1-
                                           |
                                       DC common (0 V)

Loop load voltage budget: a typical loop-powered sensor needs ≥10 V at its terminals. The 250 Ω AM2 burden drops 5 V at 20 mA. The 24 V DC rail minus 5 V leaves 19 V at the sensor, which is sufficient for most 2-wire transmitters. If the sensor requires >20 V headroom, use a 30 V DC rail or a 4-wire sensor.

6. Analog Address Mapping Rule

The number of analog input addresses reserved for the LOGO! base module is configurable in LOGO! Soft Comfort under File > Offline Settings > I/O Settings. The first AM2 expansion's I1 begins at the next free AI slot after the reserved range.

For the configuration in this article (two AM2 modules plus a base with all four shared AI reserved by default), the addressing is:

The address allocation is independent of whether the base module's AI terminals are physically wired. Reserving the slot removes it from the expansion pool. The order of AI1-AI4 on the base (I7=AI1, I8=AI2, I1=AI3, I2=AI4) is also fixed and is not affected by the reservation count setting.

7. Configuration in LOGO! Soft Comfort V8.3

1. Open the program in LOGO! Soft Comfort V8.3 (or the equivalent project in LOGO! Web Editor for the 0BA8 generation).
2. Select File > Offline Settings > I/O Settings. In older versions, this is Tools > Select Hardware > LOGO! Base Module.
3. In the I/O settings dialog, the field "Number of analog inputs on the basic module" offers 0, 2, or 4. The default is 4.
4. To make the first AM2's I1 appear at AI1 (i.e., free AI1-AI4 for the expansion), select 0 and confirm with OK.
5. Click Download > PC → LOGO! and transfer the configuration. For Ethernet-connected modules, enter the LOGO! IP address (default 192.168.0.10) in the IP field of the download dialog.

Menu path variations by version:

Important: changing the reserved slot count from 4 to 0 invalidates the existing program references to AI1-AI4. Existing FBD blocks referencing those addresses will be flagged as "Address not available" and must be re-wired. Save a backup of the project file (.lsc) before changing the setting.

8. Reading the Analog Value in the Program

Once the address is known, the standard LOGO! FBD blocks for analog signal processing are:

Example: a 4-20 mA pressure transducer with 0-10 bar output range. The scaling formula is:

EU [bar] = (Raw - 200) × (EU_max - EU_min) / (Raw_max - Raw_min) + EU_min
EU [bar] = (Raw - 200) × (10 - 0) / (1000 - 200) + 0
EU [bar] = (Raw - 200) × 0.0125

For a 4 mA signal (Raw = 200), EU = 0 bar. For 20 mA (Raw = 1000), EU = 10 bar. For 12 mA (Raw = 600), EU = 5 bar.

FBD implementation in LOGO! Soft Comfort:

1. Drag an Analog Input block (B001) and set its source parameter to AI5.
2. Set the block's Sensor parameter to 0-20 mA (matches the AM2 hardware jumper position). The Sensor list in the Analog Input block includes "0-10 V," "0-20 mA," "4-20 mA (PT100/PT1000)," and "PT100/PT1000 with climate." Select 0-20 mA when the AM2 jumper is in the I position.
3. Insert an Analog Amplifier (B005) with Gain = 0.0125 and Offset = -2.5. The offset of -2.5 corresponds to subtracting 200 raw (200 × 0.0125 = 2.5). The output of the Analog Amplifier is the EU value in bar (0-10).
4. Use the scaled output as the process variable (PV) in a PID Controller block (B014) for closed-loop pressure control, or feed it to an Analog Threshold Trigger (B003) for an alarm function.

FBD snippet (LOGO! Soft Comfort notation):

  [AI5 (AM2 #1 I1, 0-20 mA)] --> [B001 Analog Input]
                                          |
                                          v
  [Constant -2.5] --------------------->  |
                                          v
                                    [B005 Analog Amplifier
                                     Gain = 0.0125
                                     Offset = -2.5]
                                          |
                                          v
                              [B003 Threshold Trigger, ON=8.5, OFF=8.0]
                                          |
                                          v
                                     [Q1 (overpressure alarm)]

Wire break detection: the Analog Amplifier block raises an error flag (block output Ax) if the input value falls below 0 (open circuit in 4-20 mA, raw 0) or above 1000 (over-range). Wire this flag to a fault output or to a LOGO! TDE message text so a broken sensor cable is visible on the operator panel.

9. Verification Procedure

1. Connect LOGO! Soft Comfort online via Ethernet (or open the LOGO! Web Editor at http://<logo-ip>; default user "LOGO" / password "LOGO").
2. Navigate to Online > Online View (or the Web Editor's "Status" tab). The AI values appear in the status bar in real time, updated every program cycle (~10 ms).
3. Apply 4 mA to the sensor loop using a calibrator. The raw value at AI5 should read 200 ±2; the scaled EU value should read 0.00 bar.
4. Apply 20 mA. AI5 should read 1000 ±2; scaled EU = 10.00 bar.
5. Apply 12 mA. AI5 should read 600 ±2; scaled EU = 5.00 bar.
6. Open the sensor loop (0 mA). AI5 should read 0; the Analog Amplifier error flag should be high. Confirm the wire-break message appears on the TDE display.
7. Short-circuit the sensor terminals (sensor current limit, ~25 mA). AI5 should read 1000+; the over-range flag should be high.

Acceptance criteria:

• Linearity: ±0.5 % of full scale over 4-20 mA
• Repeatability: ±0.2 % over 1 hour at constant temperature
• Temperature drift: ±0.1 % per 10 K typical

Modbus TCP access: the LOGO! 8.3 base module exposes AI1-AI8 as Modbus holding/input registers. AI1-AI8 are accessible at addresses 0-7 in the LOGO! Modbus TCP server map. A SCADA master polls register 4 to read the AM2 #1 I1 value (Raw 0-1000). Enable the Modbus TCP server under File > Offline Settings > Modbus Connection; default port is 502.

If any verification step fails, consult the troubleshooting matrix in Section 11.

10. Related Platform Notes

The pattern of reserving address space for the base module and mapping expansion I/O into the remaining slots is not unique to LOGO!. Other platforms address analog I/O expansion as follows:

• Siemens S7-1200 / ET200SP – Analog input addresses are fixed in the device configuration in TIA Portal (V15 or later). Channel diagnostics (wire break, overrange, underrange, short circuit) are enabled per channel in the module properties. See the SIMATIC S7-1200 manual collection, "Analog module diagnostics" page.
• Allen-Bradley Micro800 (2085 Expansion I/O) – Analog expansion modules such as the 2085-IF4 (4 AI, ±10 V / 0-10 V / 0-20 mA / 4-20 mA) and 2085-IRT4 (4 RTD) plug into the right side of Micro850 and Micro870 controllers. Addressing in Connected Components Workbench is sequential starting at the controller's next available slot. See the Micro800 Expansion I/O Modules product page.
• Arduino Opta A0602 Analog Expansion – Provides 8 channels, each software-configurable as analog input or output, with 2 channels capable of 3-wire RTD readings. See the Opta Analog Expansion A0602 documentation.

All three platforms share the principle that the engineering tool, not the hardware position, determines the logical address of an analog input. In LOGO!, the I/O settings dialog controls the base-module reservation. In TIA Portal, the device configuration assigns IW addresses. In Connected Components Workbench, the slot order in the project tree assigns local I/O names.

11. Troubleshooting Matrix

12. FAQ