5.2. Definitions

The control extension of wanda involves some terms and expressions, which are explained here in a hierarchical fashion. After the definitions some general remarks concerning the control diagram are made.

Control components	Blocks that can be placed anywhere in the scheme. They generate one or more output signals, based on zero or more input signals (by conver­sion). To enable signals to be trans­ferred the control blocks are provided with input and output channels.
Input channel	Hot spot of control component via which one or more input sig­nals can enter. It is denoted by a triangle pointing towards a control component. The signal may be numeric or logical, denoted by respectively a filled (solid) or an empty (hollow) triangle.
Output channel	Hot spot of control component via which one output sig­nal can exit (through multiple signal lines). It is denoted by a triangle pointing away from a control component. The signal may be numeric or logical, denoted by respectively a filled (solid) or an empty (hollow) triangle.

Sensor

Component that “measures” a quantity in a hydraulic component or hydraulic node. The measured quantity can be further transferred as a signal to a input channel of a control component denoted by respectively a filled or an empty triangle.

Signal generator	Component that generates a signal autonomously. May be a con­stant, a time table or a time function.
Conditional action	Generates an event if a certain condition becomes true.
Controller	Continuously controls/steers a system based on the differ­ence (error) between a set value and a measured value.
Operator
Arithmetic	Operator that converts and combines numbers, like ‘+’, ‘-’, ‘*’ and ‘/’.
Logic	Operator that converts and combines logical values (TRUE/FALSE), like ‘AND’, ‘OR’, ‘NOT’ and ‘XOR’.
Signal line	Line connecting an output channel of a control component to an input channel of another control component. It may also come from a sensor or go to a controlled hydraulic component. Signal lines can convey numeric data as well as logical data. They are shown in the schematics as dashed lines.
Sensor line	Line connecting a hydraulic component to a sensor component. Sensor lines only convey numeric data. They are shown in the schematics as solid lines.
Controlled hydraulic component	Hydraulic component (pump, valve) to be actuated by the control system, by means of a change of the controlled variable (pump speed, pump on/off, valve position).

5.2.1. Control diagram remarks

The elements that can be applied in the control scheme are:

sensor	This element is graphically represented by a circle connected to the end of a solid line. This line is to be connected to the hydraulic compo­nent/node to be measured and conveys the measured signal. This is actually the input channel of the sensor. The output channel is situated at the middle of the circle and is the starting point of one or more signal lines.
signal line	This element is represented by a dashed line
control component	This element is represented by a box with small triangles attached. The triangles pointing towards the box are input channels, those pointing away from the box are output channels. The filled (opaque) triangles denote channels conveying numerical signals, the empty (transparent) tri­angles denote channels conveying logical signals. The class of the control component is denoted by a text within the box (COND: condition, LCS: level control switch, PID: PID con­troller, etceteras).

In the figure below an example system is shown containing the above mentioned control elements. The system consists of a valve controlling the upstream pressure. The actual upstream pressure is measured by a sensor. From here a signal line conveys the pressure value to the - numerical - input channel of the PID control component. This component converts the input value to a numerical output value (valve position), which is conveyed to the valve by a second signal line. The fact that the valve is controllable is denoted by a red dot at top of the symbol