B&R X20AT4222 RTD Input Module

The B&R X20AT4222 is a high-precision analog input module designed for measuring resistance temperature detectors (RTDs) such as Pt100 and Pt1000. Part of the X20 I/O system, this module provides 4 isolated input channels with 24-bit resolution and supports 3-wire or 4-wire connection for lead compensation. It is ideal for industrial temperature monitoring applications requiring high accuracy and noise immunity, such as HVAC, food processing, and chemical plants.

Technical Specifications

The X20AT4222 features 4 analog input channels for Pt100 or Pt1000 RTDs. Measurement range: -200°C to +850°C for Pt100. Resolution: 24 bits (0.01°C typical). Accuracy: ±0.1% of full scale at 25°C, ±0.2% over temperature range. Input connection: 3-wire or 4-wire configuration; the module automatically compensates for lead resistance. Conversion time: 10 ms per channel (sequential). Channel isolation: 500 V between channels and bus. The module includes an integrated sensor for cold junction compensation (for thermocouple models, not used here). Power consumption from X2X Link bus: 0.3 W typical. Operating temperature: -25°C to 60°C (horizontal mounting). The module is hot-swappable via X2X Link. Dimensions: 12.5 mm width (1 slot). Terminal blocks: X20TB12 (screw) or X20TB12F (spring) required, sold separately. The front panel includes LED indicators for module status and channel diagnostics.

Key Features

• 4 RTD input channels (Pt100, Pt1000, Ni100, Ni1000)

• 24-bit resolution with high accuracy (±0.1°C typical)

• Supports 3-wire and 4-wire lead compensation

• Galvanic isolation between channels and bus (500 V)

• Configurable measurement range and digital filtering

• Automatic detection of sensor wire break

• Conversion time configurable (10 ms to 100 ms per channel)

• Hot-swappable design for easy maintenance

• Compact 12.5 mm width for high-density mounting

Measurement Principle

The X20AT4222 uses a constant-current excitation method to measure the RTD resistance. For a Pt100, a 0.5 mA current source is applied, and the voltage drop across the sensor is measured with a high-impedance differential amplifier. The internal 24-bit Sigma-Delta ADC converts the analog signal to a digital value. The module calculates temperature using the Callendar-Van Dusen equation for Pt100 or linear interpolation for other sensor types. In 3-wire mode, the module measures the lead resistance twice and subtracts the error. In 4-wire mode, it uses separate sense wires to eliminate lead resistance entirely, providing the highest accuracy.

Configuration and Software

Using B&R Automation Studio, engineers can configure each channel individually. Parameters include sensor type (Pt100, Pt1000, Ni100, Ni1000), wiring mode (3-wire or 4-wire), measurement range (full or scaled), and digital filter (0-100 ms). The module outputs temperature in degrees Celsius or Fahrenheit, or raw resistance value in ohms. Scaling can be applied in the I/O mapping to obtain engineering units. Diagnostic features include wire break detection (open circuit) and short-circuit detection (sensor input below minimum value). Each channel has a status flag for validity.

Integration with X20 System

The X20AT4222 connects to the X20 backplane via X2X Link and is compatible with all X20 CPUs and fieldbus couplers (POWERLINK, PROFINET, EtherCAT). The module requires a bus module (e.g., X20BM11) and a terminal block. It automatically registers with the system and receives a unique I/O address in Automation Studio. The module supports cycle times down to 1 ms for all 4 channels (depending on configuration). The compact 12.5 mm width allows up to 64 modules on a single X2X Link bus, saving panel space.

Applications

The X20AT4222 is used in industrial temperature monitoring applications such as:

• HVAC systems (air handling units, chillers)

• Plastic injection molding (barrel temperature zones)

• Food and beverage processing (pasteurization, sterilization)

• Pharmaceutical manufacturing (incubators, freeze dryers)

• Chemical reactors and heat exchangers

• Laboratory and environmental chambers

Its high accuracy and lead compensation make it suitable for applications with long sensor cabling.

Installation and Wiring

Mount the module on a 35 mm DIN rail using standard X20 installation procedures. Insert the X20BM11 bus module to the left of the X20AT4222. Use a X20TB12 terminal block for screw-type wiring. For Pt100 sensors, connect the three or four wires as follows: channel 1 uses terminals X1 (excitation+), X2 (sense+), X3 (sense-), X4 (excitation-). The module provides a separate return for each channel. Use shielded twisted-pair cable for sensor wiring, with the shield grounded at the controller end. Avoid running RTD cables parallel to power cables. The terminal block is removable for pre-wiring.

Environmental and Compliance

The X20AT4222 is CE, UL, and ATEX Zone 2 certified. It meets EN 61131-2 standards for PLC equipment. Operating humidity: 5-95% non-condensing. Vibration resistance: 5g (10-55 Hz). Protection rating: IP20. The module is designed for pollution degree 2 environments (control cabinets). Storage temperature: -40°C to 85°C.

Conclusion

The B&R X20AT4222 RTD input module delivers precise, noise-immune temperature measurement for industrial applications. Its 24-bit resolution, 4 isolated channels, and support for 3-wire/4-wire sensors make it a reliable choice for integrating temperature sensing into X20-based control systems.