Example Of Closed Loop Pid Control - Danfoss VLT AQUA Drive FC 202 Design Manual

Introduction
are added to produce the total External Reference. The
External Reference, the Preset Reference or the sum of the
two can be selected to be the active reference. Finally, this
reference can by be scaled using 3-14 Preset Relative
Reference.
The scaled reference is calculated as follows:
( )
Y
Reference = X + X ×
100
Where X is the external reference, the preset reference, or
the sum of these and Y is 3-14 Preset Relative Reference in
[%].
If Y, 3-14 Preset Relative Reference is set to 0%, the scaling
does not affect the reference.

2.8.8 Example of Closed Loop PID Control

The following is an example of a Closed Loop Control for a
booster pump application:
VLT
Water
Pump
Illustration 2.16 Closed Loop PID Control
In a water distribution system, the pressure must be
maintained at a constant value. The desired pressure (set-
point) is set between 0 and 10 Bar using a 0–10 V
potentiometer or a parameter. The pressure sensor has a
range of 0–10 Bar and uses a two-wire transmitter to
®
VLT AQUA Drive FC 202 Design Guide
Pressure transmitter
®
MG20Z102 - VLT is a registered Danfoss trademark
provide a 4–20 mA signal. The output frequency range of
the frequency converter is 10–50 Hz.
1. Start/Stop via switch connected between
terminals 12 (+24 V) and 18.
2. Pressure reference via a potentiometer (0–10 Bar,
0–10 V) connected to terminals 50 (+10 V), 53
(input) and 55 (common).
3. Pressure feedback via transmitter (0–10 Bar, 4–20
mA) connected to terminal 54. Switch S202
behind the Local Control Panel set to ON (current
input).
L1
L2
L3
N
PE
F1
91 92 93 95
L1 L2 L3 PE
U V W PE
96 97 98 99
M
3
Illustration 2.17
12
37
18
50
53
5 kΩ
55
54
Transmitter
27
2 2