Danfoss VLT Series Programming Manual page 156

Parameter Description
22-77 Minimum Run Time
Range: Function:
0 s [ 0 - par. Sets the time desired as minimum run time
*
22-76 s] after a normal start command (Start/Jog/
Freeze). Any normal stop command will be
disregarded until the set time has expired. The
timer will start counting following a normal
start command (Start/Jog/Freeze).
The timer will be overridden by a Coast
(Inverse) or an External Interlock command.
NOTE
Does not work in cascade mode.
3.20.7 22-8* Flow Compensation
It is sometimes the case that is not possible for a pressure
transducer to be placed at a remote point in the system
and it can only be located close to the fan/pump outlet.
Flow compensation operates by adjusting the set-point
according to the output frequency, which is almost propor-
tional to flow, thus compensating for higher losses at
higher flow rates.
H (Required pressure) is the setpoint for closed loop
DESIGN
(PI) operation of the frequency converter and is set as for
closed loop operation without flow compensation.
It is recommended to use slip compensation and RPM as
unit.
®
VLT HVAC Drive Programming Guide
NOTE
When flow compensation is used with the Cascade
Controller (parameter group 25-**), the actual set-point will
not depend on speed (flow) but on the number of pumps
cut in. See below:
There are two methods which can be employed,
depending upon whether or not the Speed at System
design Working Point is known.
®
MG.11.CC.02 - VLT is a registered Danfoss trademark
H
(head)
H
DESIGN
Set Point
H
MIN
P22-87
1 2 3
Number of pumps
155
3 3