Belimo Air-Water Actuator Modbus RTU

Use cases

• Monitor actuator position and sensor values on a live cloud dashboard for remote HVAC oversight.
• Create an alert when the actuator reports a malfunction or service flag to speed up maintenance response.
• Adjust damper or valve setpoints remotely without an on-site visit, reducing travel time and cost.
• Log actuator position data over time to verify correct modulating behavior and diagnose control issues.
• Configure bus fail position and watchdog timeout remotely to ensure safe actuator behavior on communication loss.
• Track multiple Belimo actuators across sites in a single ModbusCloud project for centralized building management.

Installation

1. 1Wire the Modbus RTU bus (A and B terminals) from your ModbusCloud gateway (MCG or MLP series) to the Belimo actuator, observing correct polarity.
2. 2Set the actuator Modbus address to a unique value on the bus and configure the baud rate to 38400 to match the template.
3. 3Enable bus termination on the last device by writing to register 99, or use a physical termination resistor at the end of the bus.
4. 4Configure the setpoint source register (address 118) so the actuator accepts setpoint commands from the Modbus bus.
5. 5Import the Belimo Air-Water Actuator Modbus RTU template in the ModbusCloud portal and assign it to the correct gateway and slave address.
6. 6Optionally configure the bus watchdog timeout (address 109) and bus fail position (address 108) for safe behavior on communication loss.

Things to watch for

01

The actuator does not respond on the Modbus bus. What should I check?

Verify that the baud rate on the actuator matches 38400 as required by this template. Also confirm the Modbus slave address is unique and that A/B wiring polarity is correct.

02

Setpoint commands are sent but the actuator does not move. Why?

The setpoint source register (address 118) must be configured to select the Modbus bus as the active setpoint input. If it is set to another source, the actuator ignores Modbus setpoint writes.

03

Do I need a physical termination resistor on the bus?

Belimo actuators support software-based bus termination via register 99. Write the appropriate value to enable termination on the last device. A physical resistor is not required if software termination is active.

04

What happens if the gateway loses communication with the actuator?

The actuator moves to the position defined in the bus fail position register (address 108) after the watchdog timeout (address 109) expires. Configure both registers to ensure safe damper or valve behavior during communication loss.

Registers (20)

10 read / 10 write

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