Danfoss VLT Series Operating Instructions Manual page 28

1 Extended and Advanced Cascade Controller
Option
1
27-21 Override Limit
Range:
100% (Dis- [P27-20 - 100%]
abled)*
27-22 Fixed Speed Only Operating Range
Range:
P27-20* [P27-20 - P27-21]
28
Function:
Override Limit is the allowed offset from the set-point before a pump will immediately be added or
removed (for instance in case of a fire tab is switched on). Normal Operating Range includes a delay
that limits the system response to transients. This makes the system respond too slowly to large
demand changes. The override limit causes the drive to respond immediately. The value is entered
as a % of Max Reference (P21-12). Override operation may be disabled by setting this parameter
to 100%.
Function:
Fixed Speed Only Operating Range is the allowed offset from the set-point before a pump may be
added or removed when there are no operational variable speed pumps. The system must be outside
this limit for the time specified in P27-23 (Staging Delay) or P27-24 (De-staging Delay) before a
cascade operation may take place. The value is entered as a % of Max Reference. When there are
no operational variable speed pumps, the system will try to maintain control with the remaining
fixed speed pumps.
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MI.38.C3.02 - VLT is a registered Danfoss trademark
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VLT Operating Instructions