Basic Electronics; Functional Principle - Siemens SIPART PS2 Operating Instructions Manual

Description

3.4 Functional principle

3.3.3

Basic electronics

Figure 3-8
The basic electronics contains:
● CPU
● Memory
● Analog-to-digital converter
● Display
● Buttons
● Terminal strips to connect the option module to the basic electronics
3.4 Functional principle
Control loop
The electropneumatic positioner forms a control loop with the pneumatic actuator:
● The actual value x represents the position of the actuator spindle for linear actuators or the
position of the actuator shaft for part-turn actuators.
● The higher-level control loop provides the setpoint w.
The stroke or rotary movement of the actuator is transferred to a potentiometer using suitable
attachments, positioner shaft and a backlash-free, switchable gear drive, and then to the
analog input of the microcontroller.
The current position can also be forwarded to the positioner using an external sensor. A Non
Contacting Position Sensor (NCS) is used to record the stroke or rotary angle directly on the
actuator.
The microcontroller:
● Corrects the angle error of the shaft pick-up if necessary.
● Compares the potentiometer voltage as actual value x with setpoint w.
● Calculates the manipulated variable increments ±∆y.
The piezo-controlled inlet or exhaust air valve is opened depending on the magnitude and
direction of the control deviation (x-w). The actuator volume integrates the controller increment
for the actuating pressure y which is proportional to the drive rod or the drive shaft. This
controller increment changes the actuating pressure until the control deviation becomes zero.
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Basic electronics, schematic representation
SIPART PS2 with PROFIBUS PA
Operating Instructions, 05/2019, A5E00127926-AC