User Manual

Siemens Building Technologies VISONIK DCS Functions and System Messages VVS18 CM2U8567E / 04.1999
Landis & Staefa Division Function MXD 2-193
Size of the switchable load
Each command step (0 to 3) of a programmed DO point is assigned to a corresponding
load through parameters PN1 to PN3 (positive for real loads, negative for generators).
All DO entries can be blocked by appropriate setting of the relative 'Blocking flag'.
Blocking flags must be given "$" addresses (i.e. $FLn).
This defines that flag value at which the entry will be blocked. The prompt for 'Flag
value' will only be asked if a "Blocking flag" has already been declared.
•
When a flag becomes active, the related DO point currently in a
shedded
state will be
switched to its threshold value.
In this case, the MXD program has no more influence on such a point; it is blocked for
this point
•
If a time is active under "Min/Max Time Shed" for such a point, it will only be blocked
after any declared time has elapsed.
Minimum and maximum on/off times can be specified to protect plant equipment. Times
are in minutes.
Such times are taken into account for any MXD program DO point commands which will
only be executed after these set times have elapsed.
In spite of these defined times other programs (TRR, DRR, etc.) can still change such
DO points at any time.
The maximum times are monitored through the 'Duty cycling program (DUCY), not by
the MXD program.
A fan which should run for a minimum of 20 minutes is therefore set to:
Min Thresh. Time : = 20 (provided Threshold Value = ON)
A generator which should be connected for a minimum of 30 minutes is therefore set to:
Min Shed Time : = 30 (provided Shedded Setting = ON)
An air conditioning unit which must not be switched off for more than 60 minutes is
therefore set to:
Max Thresh. Time : = 60 (provided Threshold Value = OFF)
The MXD entry is only changed when the dialogue is executed step-by-step. The DC
Server acknowledges a properly-entered input or change by printing out the entire entry
followed by OK.
Blocking flag
Flag value
Min Thresh. Time =
Max Thresh. Time =
Min Time Shed
Max Time Shed
Example
Note