MODBUS COUPLING
The process control system (PCS) contains a mem-
ory area into which the chromatograph can write
via the
MODBUS
interface. The PCS software can
read this information. If you write into this mem-
ory area, the information is automatically sent to
the chromatograph.
Common memory area in PCS
The chromatograph and PCS thus communicate via this
memory area. The memory is divided into 16-bit regis-
ters which are accessed by means of addresses. The
maximum address range is 0 to 65535.
Declaration of memory distribution
The meaning of each register must be declared when
configuring. The results of each component in each
sample must be written by each chromatograph into a
specific position in the PCS memory. The PCS can then
find this data there again.
These address declarations depend on the number of
chromatographs, samples and components. They are
therefore redefined by us for each system.
A similar declaration is required for the status, sample
sequence and sample release. In this case the standard
addresses have fixed declarations.
Programming
the chromatograph and PCS
The chromatograph and PCS must be programmed ac-
cording to the declared memory division.
The
MODBUS
download driver must be configured
in the chromatograph.
The server generates these address lists automat-
ically, and they can then be printed.
TELEPERM COUPLING
The chromatograph and PCS communicate via
data blocks. These data blocks must be defined in
the PCS.
Interface driver
An interface driver for the
TTY/TELEPERM
coupling
must be installed in the chromatograph. This driver is a
standard, and is identical for every system. The driver
in the chromatograph is initialized/configured by the
PCS once or more often, e.g. with the number of
samples and components. This configuration is stored
by the driver in the flash
EPROM
of the chromatograph.
Programming the PCS
Programming is only necessary in the PCS. In this case,
fixed data structures are defined for the component re-
sults similar to as with the
MODBUS
and dependent e.g.
on the number of samples and components. Status
messages, sample sequence and sample release have
fixed formats.
A description for this programming is provided with
the driver. There is a user interface for this in the PCS
(Teleperm/Simatic).
Control system
RS 485
ChromLAN
No. 2 No.15
RS 485
Modbus
Control PC
mit Schniko-2
to
No. 1
Chromatographs
Direct connection to control system
with MODBUS download driver in the chromatograph
Networking
2MODBUS.CHP, Stand Dezember 22, 1999
25
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