Siemens 3RK1911-2BM21 Analog Input Module

The 3RK1911-2BM21 functions as an analog input module for the Siemens SIMATIC S5 PLC system. This unit converts analog field signals into digital values for the CPU. It accepts standard current and voltage signals from transmitters and sensors. Therefore, this module enables precise process variable monitoring in industrial automation applications.

Technical Specifications

We engineered this analog input module for high-precision signal acquisition. Its single-slot design fits directly into a standard S5 rack. Moreover, the module includes built-in filtering for noise rejection on field signals.

Parameter	Specification
Dimensions (H x W x D)	8.9 x 1.5 x 5.1 inches (226 x 38 x 130 mm)
Weight	0.52 kg (1.15 lbs)
Input Channels	8 differential analog inputs
Input Signal Ranges	0-10V, ±10V, 0-20 mA, 4-20 mA
Resolution	12 bits (4096 counts)
Conversion Time	25 ms per channel (all channels)
Accuracy	±0.5% of full scale at 25°C
Input Impedance (Voltage)	200 kΩ minimum
Input Impedance (Current)	250 Ω
Common Mode Rejection	80 dB at 50/60 Hz
Isolation	500V AC between channels and backplane
Internal Power Draw	250 mA from 5V DC backplane
Operating Temperature	0°C to 60°C (32°F to 140°F)

Input Circuit Design

The 3RK1911-2BM21 uses a multiplexed analog-to-digital converter for all eight channels. A precision instrumentation amplifier conditions each signal before conversion. Individual LED indicators show the active status of the conversion process. Consequently, you can verify module operation without external test equipment.

Signal Ranges and Configuration

This analog input module accepts four different signal ranges on each channel. Current ranges include 0-20 mA and 4-20 mA for loop-powered devices. You select the range using software configuration, not jumpers.

Conversion Accuracy and Resolution

The 3RK1911-2BM21 delivers 12-bit resolution across the full input range. Each count equals approximately 2.44 mV for the 0-10V range. The module provides ±0.5% accuracy for most industrial applications. Therefore, you can rely on consistent measurements without frequent calibration.

Noise Rejection and Filtering

This analog input module includes digital filtering to reject power line noise. The filter provides 80 dB of common mode rejection at 50 and 60 Hz. The module also integrates input signals over the conversion period. Consequently, noisy field signals produce stable, repeatable digital values.

Power Requirements and Energy Storage

The 3RK1911-2BM21 draws 250 mA from the 5V DC backplane supply. It does not require external 24V power for input signal conditioning. The module contains no battery for data retention purposes. All conversion results transfer directly to the CPU without local storage.

Isolation and Protection

This analog input module provides optical isolation between field and logic circuits. The isolation withstands 500V AC between inputs and the backplane. Each channel shares a common return path with the other seven inputs. Hence, use isolated transmitters when connecting to different voltage sources.

Installation and Wiring

Mount the 3RK1911-2BM21 into any SIMATIC S5 rack slot securely. Connect your field transmitters to the screw terminal block using shielded cable. Use a 3.0 mm flat-blade screwdriver for all terminal screw connections. Connect the shield drain wire to the ground terminal at the module end only. Always turn off system power before inserting or removing this module.