(Engine-Level Function)
| Description: | Returns the previous value of the first parameter until it changes by an amount specified by the second parameter. |
| Returns: | Numeric |
Usage:  |
Steady State only. |
| Function Groups: | Rounding Math |
| Related to: | Change | PID |
| Format: |
Deadband(Value, Delta) |
| Parameters: |
| Value |
| Required. Any numeric expression giving the value whose changes are to be limited to amounts no less than Delta. |
| Delta |
| Required. Any numeric expression giving the lower limit of the change in Value that will allow the function value to change. If Delta is less than or equal to 0, the function will always return Value. |
| Comments: | When the function is first called, its value will be that of its first parameter Value. After that, the value will remain at this initial value until the difference between Value and the function value is greater than or equal to Delta. At this point, the function value will assume the new value of Value. This has the effect of ignoring all changes in Value which are less than Delta. This is useful for ignoring "noise" in values such as analog inputs. Because VTScada performs calculations based upon changes in values, this function may be used in certain situations to minimize the number of irrelevant value changes and thereby reduce the frequency of calculations and improve performance. This function may also be used by PID to eliminate noise in the process value parameter and therefore avoid making frequent minor output changes which are irrelevant. The change specified by Delta is the absolute value of the change so a positive or negative change in Value will be treated equally. Delta should be always greater than zero. |
Example:
... If Watch(1, Deadband(InletPressure, 0.5)); [ ...
This triggers a script on startup and then again whenever the value of InletPressure changes by at least 0.5 units.
