NuAire Xboxer xbc+ Ecosmart Connect Control, Installation Manual

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34
21. 07. 20. Document Number 671954 Nuaire |
Western Industrial Estate
|
Caerphilly
|
CF83 1NA
| nuaire.co.uk
XBC+ with Ecosmart Connect (C) Control
Installation Manual
6.15.4 Writing of Values (Priority Array)
Any device on the BACnet network has the ability to write values to
other device objects.
To resolve conflicts, BACnet uses a 16 position priority array to work
out who gets priority. Any request it change the present value is stored
in the priority array at the priority level of the received request. The
object then chooses the highest priority value to become the present
value.
Shown below are examples of priority array decision making.
Case 1
Priority 1 Null
Priority 2 Null
Priority 3 Null
Priority 4 Null
Priority 5 Null
Priority 6 Null
Priority 7 Null
Priority 8 Null
Priority 9 Null
Priority 10 Null
Priority 11 Null
Priority 12 Null
Priority 13 Null
Priority 14 Null
Priority 15 Null
Priority 16 Null
Relinquish
Default 0
Case 2
Priority 1 Null
Priority 2 Null
Priority 3 Null
Priority 4 Null
Priority 5 Null
Priority 6 Null
Priority 7 Null
Priority 8 Null
Priority 9 Null
Priority 10
Priority 11 Null
Priority 12 Null
Priority 13 Null
Priority 14 Null
Priority 15 Null
Priority 16 5
Relinquish
Default 0
Case 3
Priority 1 Null
Priority 2 Null
Priority 3 Null
Priority 4 Null
Priority 5 Null
Priority 6 Null
Priority 7 Null
Priority 8 Null
Priority 9 7
Priority 10 Null
Priority 11 Null
Priority 12 Null
Priority 13 Null
Priority 14 Null
Priority 15 Null
Priority 16 5
Relinquish
Default 0
Case 4
Priority 1 Null
Priority 2 Null
Priority 3 Null
Priority 4 Null
Priority 5 Null
Priority 6 Null
Priority 7 Null
Priority 8 Null
Priority 9 7
Priority 10 Null
Priority 11 Null
Priority 12 Null
Priority 13 Null
Priority 14 Null
Priority 15 Null
Priority 16 0
Relinquish
Default 0
Present Value 7
Case 5
Priority 1 Null
Priority 2 Null
Priority 3 Null
Priority 4 Null
Priority 5 Null
Priority 6 Null
Priority 7 Null
Priority 8 Null
Priority 9 Null
Priority 10 Null
Priority 11 Null
Priority 12 Null
Priority 13 Null
Priority 14 Null
Priority 15 Null
Priority 16 0
Relinquish
Default 0
Present Value 0
Present Value 0
Present Value 5 Present Value 7
Case 1
The object looks down the list until it gets to the first non-null value. In
this case, all priority levels are empty so the (relinquish) default value of
0 is used as the present value.
Case 2
Priority 16 is now 5 so the present value becomes 5.
Case 3
Priority 9 is now 7. Priority 9 overrules priority 16 so the present value
becomes 7. Note that priority 16 is still calling for 5 but it is being
ignored.
Case 4
Priority 16 is changed to 0 but this has no effect on the present value. It
is still at 7 because of priority 9.
Case 5
Priority 9 is relinquished back to null. This allows priority 16 to take
priority again and the present value becomes 0.
The priority array is stored inside the device itself. This means that an
external device can write to a priority position and the value will stay
there even if the device is disconnected.
AI and BI object types are read only and therefore do not have a priority
array.
AO & BO values are typically changed by the strategy at priority level
16. Any override must occur above this level and is not recommend. Be
sure to relinquish all overrides once finished to minimise confusion and
undesirable operation.
AV, BV & MSV values are generally not changed by the strategy so an
external command at priority level 16 is sufficient to change the value
permanently.
The following table shows the standard use of the priority array.
Priority Application
1 Manual Life Safety
2 Automatic Life Safety
3 Available
4 Available
5 Critical Equipment Control
6 Minimum On/Off
7 Available
8 Manual Operator
9 Available
10 Available
11 Available
12 Available
13 Available
14 Available
15 Available
16 Available