Application Set-Up Examples
6.5.2.1 Example of Process PID Control
Illustration 6.19 is an example of a Process PID Control used
in a ventilation system.
Illustration 6.19 Example - Process PID Control in a Ventilation
6
6
System
In a ventilation system, the temperature is to be settable
from -5 to 35 °C with a potentiometer of 0–10 V. The set
temperature must be kept constant, for which purpose the
Process Control is to be used.
The control is of the inverse type, which means that when
the temperature increases, the ventilation speed is
increased as well, 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. Minimum/Maximum speed 300/1500
RPM.
66
Illustration 6.20 Two-wire Transmitter
1.
Start/Stop via switch connected to terminal 18.
2.
Temperature reference via potentiometer (-5 to 35
°C, 0–10 V DC) connected to terminal 53.
3.
Temperature feedback via transmitter (-10 to
40 °C, 4–20 mA) connected to terminal 54. Switch
S202 set to ON (current input).
6.5.2.2 Ziegler Nichols Tuning Method
NOTICE
The method described must not be used on applications
that could be damaged by the oscillations created by
marginally stable control settings.
The criteria for adjusting the parameters are based on
evaluating the system at the limit of stability rather than
on taking a step response. We increase the proportional
gain until we observe continuous oscillations (as measured
on the feedback), that is, until the system becomes
marginally stable. The corresponding gain (K
ultimate gain. The period of the oscillation (P
ultimate period) is determined as shown in the figure.
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) is called the
u
) (called the
u
MG35M402