Lambrecht Ser[LOG], Operator'S Manual

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LAMBRECHT meteo GmbH Ser[LOG] Manual Page 58 of 129
5.3.5.5.4 Channel type - Modbus
Ser[LOG] supports a subset of Modbus RTU and Modbus TCP. The measured values are not retrieved
by the Ser[LOG] from the Modbus devices in a block, but each measured value is always retrieved
individually. If the channel type Modbus is selected, the input mask shown below appears.
In the field "Register" the address of the start register for the measured value is entered.
The "Data type" determines how many registers are read. With "Integer (16Bit) signed" or "Word (16Bit)
unsigned" one 16 bit register is read, with "Long Integer (32Bit) signed" or "Double Word (32Bit) un-
signed" two 16 bit registers are read. In addition to the standardized data types Ser[LOG] also supports
the type Real Single, a 32 bit floating point number. For this data type Ser[LOG] offers the following
decodings independent of the endian setting:
Received byte sequence: abcd
Decoding abcd, dcba, badc, cdab
The last decoding form (cdab) is more common than the other three forms.
The standard bit sequence for Modbus is "Big Endian", but there are also devices that use "Little En-
dian". The respective bit sequence can be selected in the field "Endian".
The Ser[LOG] currently offers the Modbus functions 0x02, 0x03 and 0x04 for data retrieval in the "Mod-
bus command" field.
The "processing" of the measured value during transfer from the Modbus protocol can be carried out
according to the following rules:
Standard - Accept value only The measured value is taken over di-
rectly and fed to the measured value pro-
cessing.
Difference new value - old value The difference is calculated from the pre-
vious measured value to the current
measured value. Used, for example, to
calculate the amount of precipitation from
the total quantity since the device was
started.
Percent from 0-1 is 0% to 100% Used, for example, for status information
that is to be processed in percent.
The "divisor" is the value by which the integer value is to be divided in order to obtain a floating-point
value.
Since there is no standardized value for the timeout in the Modbus protocol, a timeout time for the
measured value can be defined in steps of 250 ms in the field "Timeout".