Example Of Process Pid Control - Danfoss VLT Decentral Drive FCD 302 Design Manual

Application Examples
Step 4: Use Table 4.23 to calculate the necessary PID
control parameters.

4.4.9 Example of Process PID Control

Illustration 4.10 is an example of a Process PID Control
used in a ventilation system.
1
ON WARNING ALARM
Bus MS NS1 NS2
W n °C
Illustration 4.13 Process PID Control in Ventilation System
Item Description
1 Cold air
2 Heat generating process
3 Temperature transmitter
4 Temperature
5 Fan speed
6 Heat
Table 4.24 Legend
In a ventilation system, the temperature is to be settable
from -5 to 35 °C with a potentiometer of 0 to 10 V. The
task of the process control is to maintain temperature at a
constant preset level.
®
VLT Decentral Drive FCD 302
100kW
2
3
®
MG04H102 - VLT is a registered Danfoss trademark
The control is of the inverse type, which means that when
the temperature increases, the ventilation speed is
increased as well, so as to generate more air. When the
temperature drops, the speed is reduced. The transmitter
used is a temperature sensor with a working range of -10
to 40 °C, 4-20 mA. Min./Max. speed 300/1500 RPM.
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 4.14 Two-wire Transmitter
1. Start/Stop via switch connected to terminal 18.
2. Temperature reference via potentiometer (-5 to
35 °C, 0 to 10 V DC) connected to terminal 53.
3. Temperature feedback via transmitter (-10 to 40
°C, 4 to 20 mA) connected to terminal 54. Switch
S202 set to ON (current input).
12
37
18
50
53
5 kΩ
55
54
Transmitter
61
4 4