Danfoss VLT Refrigeration Drive FC 103 Programming Manual page 159

Parameter Description
H (head)
Control Curve
Illustration 3.56 Square-Linear Curve Approximation
22-82 Work Point Calculation
Option: Function:
Example 1
H
(head)
H
DESIGN
Set Point
H
MIN
Par.:
22-83/
Control Curve
22-84/
22-87
Illustration 3.57 Speed at System Design
Working Point is Known
From the datasheet showing characteristics for the
specific equipment at different speeds, simply
reading across from the H
Q point allows finding point A, which is the
DESIGN
system design working point. The pump character-
istics at this point should be identified and the
associated speed programmed. Closing the valves
and adjusting the speed until H
achieved allows the speed at the no-flow point to
be identified.
Adjustment of parameter 22-81 Square-linear Curve
Approximation then allows the shape of the
control curve to be adjusted infinitely.
Example 2
Speed at system design working point is not
known: Where the speed at system design
working point is unknown, another reference point
on the control curve needs to be determined
based on the datasheet. By looking at the curve
for the rated speed and plotting the design
pressure (H , Point C), the flow at that
DESIGN
pressure, Q , can be determined. Similarly, by
RATED
plotting the design flow (Q
pressure H
DESIGN
Knowing these 2 points on the pump curve, along
MG16H202
Programming Guide
Q ( ow)
A
Q
(flow)
point and the
DESIGN
has been
MIN
, Point D), the
DESIGN
at that flow can be determined.
Danfoss A/S © 05/2016 All rights reserved.
22-82 Work Point Calculation
Option: Function:
with H as described above, allows the
MIN
frequency converter to calculate the reference
point B and thus to plot the control curve, which
also includes the system design working point A.
H (head)
H
RATED
Par.
22-88
H
DESIGN
Set point
H
MIN
Par.:
22-83/
Control Curve
22-84/
22-87
Illustration 3.58 Speed at System Design
Working Point is not Known
[0] Disabled Work point calculation not active. To be used if
speed at design point is known.
*
[1] Enabled Work point calculation is active. Enabling this
parameter allows the calculation of the unknown
system design working point at 50/60 Hz speed,
from the input data set in:
•
Parameter 22-83 Speed at No-Flow [RPM].
•
Parameter 22-84 Speed at No-Flow [Hz].
•
Parameter 22-87 Pressure at No-Flow
Speed.
•
Parameter 22-88 Pressure at Rated Speed.
•
Parameter 22-89 Flow at Design Point.
•
Parameter 22-90 Flow at Rated Speed.
22-83 Speed at No-Flow [RPM]
Range: Function:
Size [ 0 - Resolution 1 RPM.
related par. Enter the speed of the motor in RPM at
*
22-85 which flow is 0 and minimum pressure H
RPM] is achieved. Alternatively, enter the speed in
Hz in parameter 22-84 Speed at No-Flow
[Hz]. If parameter 0-02 Motor Speed Unit is
set to RPM, parameter 22-85 Speed at Design
Point [RPM] should also be used. Closing
the valves and reducing the speed until
minimum pressure H
determines this value.
D
B
A
C
Q Q
Q
DESIGN RATED
(flow)
Par. Par.
22-90
22-89
MIN
is achieved
MIN
157
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