892 J006 MNAH | PGC5000 G EN 2 | 99
5.8 Remote communications overview
The analyzer allows for communications (data transfer) by Ethernet TCP/IP. The analyzer can act as a
Modbus Slave and send data to a Modbus Master. Mapping of Modbus data is performed by using a
Comma Separated Value file (.csv). The analyzer can also send data to a STAR Server or an OPC
Server.
5.8.1 MODBUS overview
MODBUS is a communications protocol used with programmable logic controllers (PLCs). It is a de
facto standard communications protocol in industry and is a commonly available means of connecting
industrial electronic devices. MODBUS allows for communication between many devices connected to
the same network; for example, a system that measures temperature and humidity and
communicates the results to a computer. MODBUS is often used to connect a supervisory computer
with a remote unit in supervisory control and data acquisition (Master/Slave).
5.8.2 PGC5000 MODBUS configuration
The MODBUS interface can be either TCP/IP or RS232 directly from the analyzer or from the
Communication Gateway server. The MODBUS software translates data from the ABB analyzer system
into the MODBUS RTU format recognizable by standard DCS Communication Gateway devices.
It is beyond the scope of this manual to describe the MODBUS protocol. Consult DCS documentation
for an explanation of concepts and terminology that may be unfamiliar to you.
The MODBUS protocol provides a set of rules which allows data to be passed between any two
compatible devices. The protocol defines how the data is to be transferred but does not define the
contents of the data. For the analyzer/DCS interface to operate, both the Communication Gateway
(with MODBUS software) and the DCS must be configured to define the functions to implement and
the corresponding data addresses to use. The MODBUS interface provides analytical composition data
from the analyzer system to the DCS and various status information (e.g. data validity, analyzer and
new data availability). The MODBUS interface also accepts limited analyzer control functions from the
DCS (e.g., request for calibration, stream activation, etc.).
The analyzer creates data tags supported by the MODBUS interface and the OPC Server. The tags not
added to the local MODBUS include the string tags ANALYSIS_NAME, COMPONENT.NAME, etc. (shown
in the bulleted list below) as these strings do not fit within the MODBUS structure of 16-bit data
registers.
A .csv file used to map data points must be identical to the one used by the MODBUS client connected
to the OPC Server. Each line of the .csv file contains at least three entries, (tag name, MODBUS slave
address, MODBUS point address). The MODBUS point address is a five-digit number which implicitly
defines the MODBUS data type based on the most significant digit as follows:
⎯ 00001-09999 STATUS COILS
⎯ 10001-19999 INPUT STATUS
⎯ 30001-39999 INPUT REGISTERS
⎯ 40001-49999 HOLDING REGISTERS
The MODBUS interface differentiates among the four different types of MODBUS data.
The MODBUS map is configured to overlay addresses. Two different data tags can map to the same
address, but one tag cannot map to two different addresses. If the latter is implemented, only the first
tag in the map is updated. Most of the data tags from the instrument are discrete indications mapped
to either input coil or status coil addresses. Tags used for control purposes must be mapped to a
status coil address since the MODBUS master cannot write to an input coil. Analog values associated
with a component measurement, as well as temperatures, pressures, and set points available from
the DTC and EPC, may be represented to the MODBUS in one of four formats:
⎯ The integer portion of the analog value will be placed in a single MODBUS register.
⎯ The IEEE floating-point format is used to store the value in two consecutive MODBUS
registers.
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