Value limit describes the status of the value with regard to its defined limits. Limits values are always defined within the configuration of particular object or structure item.
Limits might be defined only for some object types and for object value types.
D2000 system allows to define four limits: VHL, HL, LL and VLL. A limit can be defined either directly - by entering a value, or its value can be determined by a system object (dynamic limit) - the button right from the input field.
| VHL | Very High Limit - the highest limit |
| HL | High Limit - high limit |
| LL | Low Limit - low limit |
| VLL | Very Low Limit - the lowest limit |
Values of individual limits determine the state of the object value according to its value. The relation
object value - limits gives 6 possible states.
| Limit | Object status according to the relation Object value - Limit |
|---|---|
| Above VHL (object value > VHL) | |
| VHL | |
| Above HL (HL < object value ≤ VHL) | |
| HL | |
| Normal (LL ≤ object value ≤ HL) | |
| LL | |
| Below LL (VLL ≤ object value < LL) | |
| VLL | |
| Below VLL (object value < VLL) |
As the limits can be dynamic, i.e. determined by the object value (real or integer type), a
situation, when the relation VLL<LL<HL<VHL is not valid (limit crossing), may occur. The
object value is then in the status Limits Problem.
Hysteresis
Configuration of the hysteresis relating to the limits defined for the object value. The hysteresis
value (in %) is determined by the difference |VHL-VLL|. Hysteresis has effect on evaluation
of limit states of the object. Hysteresis is demonstrated on the following figure.
The object value is in the status InLimit. This value breaks the limit HL (we assume, that the object
value will not break the level HL+HYSTERESIS - it is within the red-colored area in the figure).
The value status is still InLimit. The system assigns the value state HL to the object as soon
as the value breaks the level HL+HYSTERESIS (the value is above the red-colored area in the
figure). This is valid also when the value is decreasing. The value gets the status InLimit as soon as it
falls bellow the level HL-HYSTERESIS (the value is below the red-colored area in the figure).
