The SM 1234 is a versatile analog I/O expansion module designed for the SIMATIC S7-1200 PLC system. This compact module provides four configurable differential analog inputs and two outputs, supporting both voltage and current modes—ideal for flexible and precise signal interfacing in automation systems.
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Technical Specifications
Feature Details
Analog Inputs (AI) 4 differential inputs, selectable per 2-channel group as Voltage (±10 V, ±5 V, ±2.5 V) or Current (0–20 mA, 4–20 mA)
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Analog Outputs (AO) 2 configurable outputs: Voltage (±10 V, 14-bit) or Current (0–20 mA or 4–20 mA, 13-bit)
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Accuracy Inputs: ±0.1 % (25 °C), ±0.2 % (–20 °C to +60 °C); Outputs: ±0.3 % (25 °C), ±0.6 % (–20 °C to +60 °C)
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Conversion Time Inputs: 625 µs; Outputs settling: Voltage ~300–750 µs, Current ~600 µs–2 ms based on load
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Diagnostics Supports alarm detection: overflow/underflow, short-to-ground (voltage outputs), wire-break (current), low supply voltage
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Resolution Inputs: 12 bits + sign; Outputs: Voltage 14 bits, Current 13 bits
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Power Usage Power dissipation ~2.4 W; SM-bus (5 V) consumption ~80 mA; 24 V DC consumption ~60 mA (no load)
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Physical Dimensions 45 × 100 × 75 mm; Weight: ~220 g
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Environmental & Standards Operating temperature –20 °C to +60 °C (horizontal), +50 °C (vertical); IP20 rating; Compliant with CE, UL/cULus, CSA, FM, RCM, KC, and Marine standards
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Cable Length Support Up to 100 m using shielded, twisted-pair cables
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Engineering Highlights

High Flexibility: Inputs and outputs can be dynamically configured as voltage or current in grouped pairs, suiting varied field device requirements.

Precise Signal Handling: Excellent resolution and accuracy support use cases requiring fine control, like actuator modulation or process feedback loops.

Fast Response: Sub-millisecond signal conversion and output stabilization ensure responsive automation applications.

Robust Diagnostics: Built-in detection of signal integrity issues and power faults helps minimize system downtime.

Compact & Energy-Efficient: Small footprint, low weight, and modest power usage make it perfect for dense control layouts.

Industrial-Grade Reliability: Designed for tough environments with wide temperature range and broad approvals for safety and EMC.

Ideal Applications

Multi-channel analog control applications where both input and output are required in a tight space.

Systems employing mixed signal types (voltage and current) for sensors and actuators such as actuated valves or variable frequency drives.

Accurate process control loops—temperature, pressure, or speed regulation—where precision and fast updates are essential.

Retrofitting or upgrading S7-1200 installations that require analog interfacing with diagnostics.

Summary Table
Specification Details
Input Channels 4 (voltage/current selectable)
Output Channels 2 (voltage/current selectable)
Input Accuracy ±0.1 % / ±0.2 %
Output Accuracy ±0.3 % / ±0.6 %
Conversion Time Inputs: 625 µs; Outputs: 300 µs–2 ms
Power Consumption ~2.4 W; SM bus ~80 mA; 24 V ~60 mA (no load)
Dimensions 45 × 100 × 75 mm; 220 g
Ambient Temp –20 °C to +60 °C
Cable Support Twisted shielded up to 100 m