TIA_Portal_technology_Object.pdf

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Using technology functions
Using technology functions
This chapter contains the following information:
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PID control
Motion Control
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PID control
PID control
This chapter contains the following information:
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Principles for control
Configuring a software controller
PID control (S7-1200, S7-1500)
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Principles for control
Principles for control
This chapter contains the following information:
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Controlled system and actuators
Controlled systems
Characteristic values of the control section
Pulse controller
Response to setpoint changes and disturbances
Control Response at Different Feedback Structures
Selection of the controller structure for specified controlled systems
PID parameter settings
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Controlled system and actuators
Controlled system and actuators
Controlled system
Room temperature control by means of a heating system is a simple example of a controlled system.
A sensor measures the room temperature and transfers the value to a controller. The controller com‐
pares the current room temperature with a setpoint and calculates an output value (manipulated varia‐
ble) for heating control.
A properly set PID controller reaches this setpoint as quickly as possible and then holds it a constant
value. After a change in the output value, the process value often changes only with a time delay. The
controller has to compensate for this response.
Actuators
The actuator is an element of the controlled system and is influenced by the controller. Its function
modifies mass and energy flows.
The table below provides an overview of actuator applications.
Application
Liquid and gaseous mass flow
Solid mass flow, e.g., bulk material
Flow of electrical power
Actuators are distinguished as follows:
Actuator
Valve, shutter, gate valve
Articulated baffle, conveyor, vibrator channel
Switching contact, contactor, relay, thyristor
Variable resistor, variable transformer, transistor
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Proportional actuators with constant actuating signal
These elements set degrees of opening, angular positions or positions in proportion to the output
value. The output value has an analog effect on the process within the control range.
Actuators in this group include spring-loaded pneumatic drives, as well as motorized drives with po‐
sition feedback for which a position control system is formed.
An continuous controller, such as PID_Compact, generates the output value.
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Proportional actuators with pulse-width modulated signal
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Controlled system and actuators
These actuators are used to generate the output of pulses with a length proportional to the output
value within the sampling time intervals. The actuator - e.g. a heating resistor or cooling apparatus -
is switched on in isochronous mode for durations that differ depending on the output value.
The actuating signal can assume unipolar "On" or "Off" states, or represent bipolar states such as
"open/close", "forward/backward", "accelerate/brake".
The output value is generated by a two-step controller such as PID_Compact with pulse-width mod‐
ulation.
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Actuators with integral action and three-step actuating signal
Actuators are frequently operated by motors with an on period that is proportional to the actuator
travel of the choke element. This includes elements such as valves, shutters, and gate valves. In
spite of their different design, all of these actuators follow the effect of an integral action at the input
of the controlled system.
A step controller, such as PID_3Step. generates the output value.
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