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Siemens Climatix OEM Partner

Modbus & M-Bus integration

Heat meters, pressure measurements, pumps and third-party devices belong in the control system. We connect them to Siemens Climatix - via Modbus RTU, Modbus TCP and M-Bus - and provide the data to the building management system via BACnet.

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Climatix S400 interfaces

Modbus RTURS-485 interfaces, 1,200 to 115,200 baud, cable length up to 1,000 m at 9.6 kbaud; termination and biasing via software
Modbus TCPVia Ethernet, as client or server
M-BusExtension module POL937 for up to 5 meters and 200 data points, cable length up to 300 m
BACnetApplication objects as BACnet objects for the building management system
Analogue4…⁠20 mA directly at the controller, e.g. for pressure and differential pressure measurement

Heat meters via M-Bus (POL937)

The POL937 module reads M-Bus meters and provides the values to the S400 via the internal extension bus. What matters in practice:

  • Know the addresses in advance: there is no automatic meter scan - primary and secondary addresses must be known.
  • Adjust the polling interval: the factory setting reads hourly. For control purposes the interval must be reduced to a few seconds.
  • Mind the meter dynamics: depending on the meter type, the meter itself only updates every few seconds - fast control loops need fast sensors.
  • Read the LED correctly: a red bus LED is normal without a running application; orange indicates incorrect parameterisation.

Modbus mapping without nasty surprises

  • Keep register types apart: writable values in holding registers, readable values in input registers.
  • 32-bit values: transfer meter readings via two registers and combine them - otherwise they overflow at 16 bits.
  • Check the address offset: query a known, fixed register first to rule out off-by-one errors.
  • Limit the request size: a maximum of 123 registers per read request.

Frequently asked questions

How many M-Bus meters can an S400 read?

With one POL937, up to 5 meters with a combined total of up to 200 data points. One POL937 is possible per S400.

Can the S400 deliver data to a building management system?

Yes, via Modbus TCP/RTU as a server or via BACnet. We define the mapping so that the BMS receives exactly the values it needs.

Our Modbus values are always 0 - what's wrong?

Common causes are a wrong register type, an address offset of one, or an incorrectly set read/write direction in the mapping. With systematic diagnostics this is usually found quickly.

Can 4…⁠20 mA pressure sensors be integrated too?

Yes, directly at the S400's multifunction inputs - including conversion to bar and differential pressure calculation.

More topics

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Got a project in mind?

Send us your plant schematic or functional description - we will get back to you with an initial assessment.

Email info@bo4.systems

Siemens and Climatix are trademarks of Siemens AG. BO4 Systems GbR is a Siemens Climatix OEM Partner.