BECKHOFF DK9322-0810-0036 - Manual (Page 2)

TwinCAT
TwinCAT, Building Automation
Application Note DK9322-0810-0036
standardized) data or control characters. Before using new slaves it is therefore important to verify compatibility with the
evaluation unit. All manufacturers of M-Bus meters offer downloadable specifications of the M-Bus protocols for their meters.
2. Typical field devices
The field devices used for M-Bus are typically meters for measuring tasks within a building. Examples of field devices include
heat meters, water meters, hot water meters, electricity meters, pulse meters, switching devices, and heating cost distributors.
A distinction is made between the reading mode. For local reading only one meter is connected, for remote reading several
meters are integrated. The following data transfer options are available, depending on the reading type. The transfer protocol
according to IEC 870 and EN1434-3 is used for all transfer routes.
2.1 Local reading (single meter)
– one optical interface (EN 61107 section 3.2)
– one inductive interface (CEN TC176/WG4)
– one 20 mA current loop, CL (EN 61107 section 3.1)
2.2 Remote reading (several meters)
– one two-wire fieldbus, meter bus (CEN TC176/WG4)
– one 11-bit modem
– radio system (433 or 868 MHz)
3. Master versions
The master can be an independent device or a PC with level converter. It reads the data of the connected field devices at
configurable intervals and stores the meter readings permanently. In conjunction with the KL6781 M-Bus master terminal and
the TwinCAT PLC M-Bus library, all Industrial and Embedded PCs from Beckhoff as well as the BC and BX series Bus Terminal
Controllers can be used as M-Bus master. The Beckhoff Bus Terminal Controllers from the BC and BX series (except for BCxx50)
can also be used as a master, although in this case the limited transfer rates, the limited multi-tasking functionality and the
longer cycle times must be taken into account. In addition, the program memory and, consequently the mapping is limited
depending on the Bus Terminal Controller, so the number of meters that can be read is limited as a result.
Notes regarding the use of devices from the Beckhoff BC/BX series:
M-Bus devices may deliver very large values (that may exceed the DWord value range) and are therefore output in string
format. Conversion to the Real format may result in inaccuracies or even invalid values. Conversion to the LReal format is
therefore preferable. This approach is not available on controllers from the BC/BX series. If the values have to be provided in a
number format, controllers from the BC/BX series are unsuitable if those values exceed the DWord value range.
New Automation Technology Beckhoff 2
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