User Manual

Siemens Building Technologies VISONIK DCS Functions and System Messages VVS18 CM2U8567E / 04.1999
Landis & Staefa Division Function MXD 2-191
Several entries may be made for each address in the MXD register.
Application:
The same load can, for example, be assigned to both a high tariff grup and
to a low tariff group.
If a number is entered which is already used, the VISONIK DCS lists the contents of the
entry and returns to CHange mode.
All loads that belong to the same tariff are collected into one tariff group. Each tariff or
meter group represents
one
energy supply point (MD Point) and is wholly independent
of any other tariff group.
Every load must be assigned to a tariff or meter group. Up to seven such groups (1 to 7)
are definable.
The tariff group corresponds to parameter TGRP of the MD point.
Tariff/Meter Grp 0
cannot
have any load assigned to it.
Tariff group 0
means: the
maximum demand program for this tariff group is inactive. All MXD Reactions of the
related MD point can be suppressed. This is advantageous, for example, for an for
anon/off peak tariff changeover involving the same loads.
Each Tariff/Meter Group can be divided into 100 switching priorities.
The MD program:
•
sheds loads having lower priorities (small numbers) first and reconnects them last.
•
sheds loads with higher priorities (larger numbers) last and reconnects them first.
•
switches, in a round-robin sequence, loads having equal priorities, i.e. the load which
has remained unchanged by the MXD program the longest is switched first.
(This is set by the SYSTEM.)
The system value is the load step command entered in the MXD register. It is set by the
DC Server using TRR, DRR, PRR manual actions, etc.
(i.e. external to the MXD). The system value cannot be changed, either by the MD
program or manually in MXD. However, it provides the MXD program information about
the status the switch command (DO) should have when MXD has no influence on the
desired "DO position".
The
threshold
value is that value of switched step from which loads (positive loads) are
shed, or from which generators (negative loads) are reconnected.
After being switched, both types of positive and negative loads are in the 'Shedded
Value' states (=reduced load).
Threshold value
(high load)
Shedded value
(reduced load)
Positive loads
From step 3
From step 2
From step ON
to step 2
to step OFF
to step OFF
Negative loads (generators)
From step OFF to step ON
Entry =1
Tariff/Meter Grp=1
Tariff group 0
Priority =1
System Value
Threshold/Shedded
Value
Example: