User Manual

CM2N8895en / 26.02.01 Siemens Building Technologies
4/4 Landis & Staefa Division
The plant tasks created are loaded and started when the VISONIK BPS is
commissioned. The following illustration is a simplified schematic presentation of how
the plant tasks are processed in the DDC program using the example given above.
PLTn
CONTROL PSTA
DISPATCH
DSPn
RGB
TSKn
DSPn
Initialization
Control
$060 Fan
$050 Heating valve
Remote
Local
Manual
Fault
$040 Pump
$030 Damper
8895Z03en
.
TAG = 1 1 w
1
1
:
Loop
The following elements and functions are involved in processing the plant task:
Element Function
Initialization This part contains the start conditions for the plant. The initialization
process is only implemented during commissioning and program start.
Control This part is processed cyclically (loop). It contains all the data and
functions necessary for plant control.
PLTn The plant commands are acquired from the various sources:
– “Remote” from the VISONIK data and communication server (DCS),
e.g., a command from the VISONIK peak demand limiting program.
– “Local” from the VISONIK BPS, e.g., the TSP time switch program.
– “Manual” = Operator input via the VISONIK BPS or VISONIK DCS.
– “Fault” = Error in plant/plant faults.
CONTROL The COLBAS instruction CONTROL triggers a calculation of the new
PSTA set plant state at every cycle.
PSTA The set plant state is determined at each polling according to the
current plant commands and their priorities, and then assigned to the
PSTA parameter. The PSTA is subsequently transmitted to the
DISPATCH system procedure.
DSPn Dispatcher point: The virtual data point assigned to the PLTn plant
point. It contains, among other things, the operating state table.
DISPATCH The DISPATCH plant procedure selects the values assigned to the set
plant state (here DAY) from the operating state table and assigns them
to the plant elements or the RGB controller block. The RGB then uses
these values to generate the corresponding manipulated variable for
the heating valve.
RGB Controller block (virtual data point), here for the supply air temperature.
The controller block controls the supply air temperature to the
predefined setpoint for DAY operation.
Refer to the following documents for more information on this topic:
Document No. Title
CM2B8301E BPS user’s guide
CM2T8567E VISONIK System Basics (expert documentation)
Plant task
Block diagram
Elements and
functions
Additional information
 2001 Siemens Building Technologies Ltd.