User Manual

CM2U8567E / 04.1999 VISONIK DCS Functions and System Messages VVS18 Siemens Building Technologies
2-192 Function MXD Landis & Staefa Division
The
shedded value
is that value of switched step from which loads (positive loads) are
connected, or generators (negative loads) are disconnected.
After being switched both positive and negative type loads are in then in a state equal to
the 'threshold value' (= larger load).
Shedded Value
(reduced)
Threshold Value
(high load)
Positive loads
From step OFF
From step OFF
From step 2
to step ON
to step 2
to step 3
Negative loads (generators)
From step ON to step OFF
Both threshold and shedded values may also act on stepped loads (0-1-2-3-2-1-0)
provided the SYSTEM VALUE permits such switching.
SYSTEM VALUE: OFF
The MXD program cannot reconnect any loads.
SYSTEM VALUE: Step 2
The MXD program will not switch a load to step 3 even if this was calculated as
possible for a small load. However, it is completely acceptable to switch large loads
down to steps 1 or 0 if they have been entered in the maximum demand register.
It is therefore possible to issue an ON command to a DO point which is included in the
MXD program from an external program (e.g. PRR,TRR, etc.) or even manually. But it
could happen that an OFF command is issued immediately afterwards to the same DO
point by the MXD program, depending on the load demand situation (i.e. load too large).
N o t e:
•
If the
Shedded value
is equal to or less than the
System value
, the MXD program
can switch loads.
•
If the
Threshold value
is larger than the
System value
, the MXD program will not
execute the command.
MXD Requirements
The MXD program is, however, only active under the following conditions:
•
An entry for the related load must exist in the MD register.
•
Parameters DO1ACT/FLI1ACT and DO1ACT/FLI2ACT must not be active.
•
"RVAL" must result from parameter DO and not from the DO1 or DO2 parameters.
•
Any set blocking flag must not be active.
•
Any times set under "Min/Max Time Shed" must have elapsed.
Priorities
All other programs, including operator manual actions, have higher priorities than MXD.
If a load has been switched through another program (i.e., TRR, PRR, etc.) or manually,
the MXD program, in accordance with its shedded value, cannot override this action.
(see example on SYSTEM VALUE).
Shedded value
Example:
Example