TXM1.8RB SIEMENS

TXM1.8RB Siemens Basis unit

Brand：SIEMENS Model number：TXM1.8RB

Country of origin: Germany Product weight：0.55kg

HS code：8517623990

Product Details：

Product Dimensions：

The TXM1.8RB serves as a decentralized I/O point that communicates with a Desigo PXC modular controller via the TX-I/O island bus. It features eight independent digital outputs, each equipped with a bistable relay. A key characteristic of the "RB" variant is the inclusion of local override switches (Hand-Off-Auto) on the front panel, allowing maintenance personnel to manually control the relay states for testing or emergency purposes. The bistable nature of the relays ensures that they maintain their last state even if power is lost, which is critical for specific safety and process stability requirements.

Product Parameters

The technical specifications of the TXM1.8RB highlight its suitability for robust building automation tasks:

Number of Outputs: 8 Digital Relay Outputs.
Relay Type: Bistable (latched), ensuring state retention during power failure.
Switching Voltage: Supports AC/DC between $24 \text{ V}$ and $250 \text{ V}$ .
Current Rating: Up to $5 \text{ A}$ (resistive) or $2 \text{ A}$ (inductive) per output.
Operating Voltage: $24 \text{ VDC}$ supplied via the TX-I/O island bus.
Power Consumption: Approximately $1.4 \text{ W}$ during operation.
Bus Connection: Integrated connection to the TX-I/O island bus for data and power.
Protection Class: IP20 according to EN 60529.
Mounting: Standard DIN rail mounting ( $35 \text{ mm}$ ).
Dimensions: Standard TX-I/O width (modular width).

Product Advantages

One of the primary advantages of the TXM1.8RB is its Local Override Capability. The front-mounted manual switches provide immediate tactile control and visual feedback through LED indicators, which significantly simplifies commissioning and troubleshooting. Because it uses Bistable Relays, the module is energy efficient; power is only consumed when the relay is changing state, rather than continuously to hold the relay closed.

Furthermore, the High Switching Capacity allows the module to directly control motors, fans, and lighting circuits without needing additional intermediate relays in many cases. The Seamless Integration into the Desigo platform means that once the module is plugged into the island bus, it is automatically recognized and configured by the controller, reducing engineering time.

Important Considerations and Precautions

When installing and operating the TXM1.8RB, several safety and technical precautions must be observed. First, always Verify Voltage Ratings before connection; while the relays can handle up to $250 \text{ VAC}$ , ensure that the wiring and insulation used meet the required safety standards for high-voltage applications.

Second, pay attention to Current Limits. Exceeding the $5 \text{ A}$ threshold can weld the relay contacts or cause thermal damage to the module. For highly inductive loads like large motors, ensure external suppression or contactors are used if the inrush current exceeds the module's specifications.

Third, the Island Bus Capacity must be calculated. The total power consumption of all TXM modules on a single bus segment must not exceed the output capacity of the PXC controller or the TXS1.12F10 power supply module. Finally, ensure the module is installed in a clean, dry environment within its IP20 rating, typically inside a locked control cabinet to prevent unauthorized manual override of the relays.

Product Applications

The TXM1.8RB is widely used in commercial and industrial building management systems:

HVAC Control: Switching fans, pumps, and small electric heaters on and off based on environmental demands.
Lighting Management: Controlling lighting circuits in large areas, often integrated with timers or occupancy sensors.
Motor Control: Direct switching of small single-phase motors used in dampers or ventilation units.
Interfacing with Third-Party Systems: Sending dry-contact signals to fire alarm systems, elevators, or security panels to trigger specific building-wide responses.
Redundancy Systems: Utilizing the bistable feature to ensure that critical ventilation remains in its last known state during a temporary control power loss.

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