User Manual

Siemens Building Technologies CM2N8895en / 26.02.01
Landis & Staefa Division 3/4
Before the control of a building services system can be programmed, all the states a
plant must assume have to be defined in a first step. The outcome of these
considerations gives the list of set plant states. These could be the following for the
example previously shown:
• Plant OFF.
• Day operation (controlled to comfort temperature).
• Night operation (controlled to reduced temperature).
• FROST
In a second step, the operating states of the plant elements (valves, air dampers, fans,
pumps, etc.) for the individual set plant states must be determined. Example:
The plant elements must assume the following operating states for the set plant state
FROST.
• Damper Closed (0)
• Pump ON (1)
• Heating valve Open ( 100 = 100% stroke)
• Fan OFF (0)
The previous considerations are summarized in the operating state table. If the
operating states for the defined, set plant states have been determined for all the plant
elements, a matrix like the following results:
Damper
Pump
Heating valve
Fan
($ 030.ADR)
($ 031.ADR)
($ 050.ADR)
($ 060.ADR)
Plant
OFF
0
Operation
DAY
1
Frost
3
Operation
NIGHT
2
Plant elements
8995Z01en
Set plant states
PSTA
0
0
0
0
0
1
100
0
1
1
w
2
1
1
1
w
1
1
w
1
,w
2
= Reference variable
PSTA (= Plant STAte) is a PLTn plant point parameter. It receives the set plant state
valid in each case as a numerical value, for example, PSTA=3 for FROST. The PSTA
parameter is calculated cyclically from the current plant commands and the priorities
assigned during programming.
During engineering, a plant task is created as part of the overall plant operating
program. When this task is created, the following must be taken into consideration:
– Which influences and events must be acquired and where must they be collected to
allow the defined plant state to be detected or specified?
– What elements are used for this (sensors, switches, programs, manual control
operations, local/remote)?
– Which VISONIK BPS measuring and control commands (basic and processing
functions) must be used to achieve the required operating states?
After that, the software tools are created using:
– Function blocks from program libraries, predefined and tested.
– COLBAS commands for special, user-specific functions (COLBAS stands for Control-
Oriented Language for Building Automation Systems)
.
Definition of the
plant functions
Set plant states
Plant element
operating states
Operating state table
PSTA parameter
Implementation of the
plant task