Service manual

14 Siemens-Elema AB E382 E380E 061 01 03 01
Introduction Servo Ventilator 300/300A
1
Feedback control system – General
Any CONTROLLING SYSTEM may comprise one
single CONTROLLER or, for instance, a cascade
of more than one CONTROLLER. Compensating
elements may also be added.
CONTROLLER symbol used in
this chapter.
In each CONTROLLER, the actual value normally
from a TRANSDUCER in the CONTROLLED SYSTEM is
compared to the desired value = REFERENCE
VARIABLE
. The difference between these two
input values results at the output of the
controlling system in an ACTUATING SIGNAL.
Each CONTROLLER may comprise some
combination of the following parts:
• Proportional action, P
• Integral action, I
• Derivative action, D.
P-action gives a continuous basic positioning.
I-action gives a slowly varying positioning
compensation for small long time deviation.
D-action gives a speed-up positioning
reaction at (fast) changes.
The signals from these parts (from the parts
used in the actual combination) are added.
The sum is the total ERROR SIGNAL which may
be converted before use as an ACTUATING
SIGNAL
.
Each CONTROLLING ELEMENT (in the ventilator:
inspiratory valves and expiratory valve) is
positioned by the ACTUATING SIGNAL from its
controlling system. Feedback control, which
is synonymous with regulation, results in the
controlled valve being moved into such a
position that the ACTUAL VALUE is kept equal to
the DESIRED VALUE independently of
disturbance variables like changes in the
airway resistance or lung compliance.
P
D
I
CONTROLLING
ELEMENT
"COMPENSATOR"
CONTROLLING SYSTEM
COMPARING
ELEMENT
CONTROLLED SYSTEM
TRANSDUCER
ACTUAL
VALUE
ACTUATING
SIGNAL
REFERENCE
VARIABLE
DESIRED
VALUE
"ERROR
CALCULATOR"
ERROR
SIGNAL
CONVERTER
PID-CONTROLLER
300-A08E
SIGNAL AMPLIFIER
(WITH SERVO)