Pneumatic actuators are available in single and double-acting versions. In a single-acting
version, only one pressure chamber is ventilated and depressurized. The pressure developed
works against a spring. In a double-acting version, two pressure chambers work against each
other. Ventilating the volume of one chamber simultaneously depressurizes the volume of the
other.
Control algorithm
The control algorithm is an adaptive, predictive five-point controller.
In case of large control deviations, the valves are controlled using permanent contact. This
takes place in the so-called fast step zone.
In case of medium control deviations, valves are controlled using pulse-length modulated
pulses. This takes place in the so-called slow step zone.
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Figure 3-9 Functional principle of five-point controller
Small control deviations do not send control pulses in the zone. This takes place in the so-called
adaptive deadband. The deadband adaptation and the continuous adaptation of minimum
pulse lengths in "Automatic" mode ensure the best possible control accuracy with the smallest
number of operating cycles. The start parameters are determined during the initialization phase
and stored in the non-volatile memory. The most important start parameters are:
● The real actuator travel with end positions
● Travel times
● The deadband size
The number of fault messages, changes in direction, and the number of total strokes are
continuously determined during operation and saved every 15 minutes. You can read and
document these parameters using communication programs such as SIMATIC PDM and AMS.
By comparing the old values with the current ones, you can draw conclusions about the wear
and tear of the valve. You can use the diagnostics function for this.
Description
3.4 Functional principle
SIPART PS2 with PROFIBUS PA
Operating Instructions, 05/2019, A5E00127926-AC 31
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