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Data Description
| Data | Unit | Description | ||
| Set | Item | Type | Native | |
| Equipment Properties | Step Between Control | The number of steps between applications of control. Entering '1' applies control at every step. | ||
| Monitored Data Item | The monitored data item. | |||
| Proportional to Controlled Data Item | If checked (True) an increase in the controlled variable value will result in an increase in the monitored variable value. If not checked (False) and increase in the controlled variable value will result in a decrease in the monitored variable value. | |||
| Target Data Item | The target value data item. | |||
| Target Value | The target value. | |||
| Tolerance |
The convergence tolerance as a relative error.
Relative error = (value - target) / target |
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| Controlled Data Item | The controlled data item. | |||
| MaxFracChange | Fraction or Percent | Fraction | The maximum allowed fractional change in the controlled value. | |
| Lower Bound | The controlled value's lower limit. | |||
| Upper Bound | The controlled values upper limit. | |||
Equipment Properties
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Example of using equipment
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Method&Equations
To drive the monitored variable to a target value, the Controller uses an error function and this is expressed as follows:
GUESS = ((ERROR * (OLDCON - VALCON)) / (ERROR - OLDERR)) + VALCON
where:
GUESS is the new value for the controlled variable
ERROR is the relative difference between the current value of the monitored variable and the target
OLDCON is the value of the controlled variable the last time control was applied
VALCON is the current value of the controlled variable
OLDERR is the relative difference between the monitored variable and the target value the last time control was applied
Relative differences are calculated as:
ERROR = (VALMON - TARGET) / TARGET
where:
VALMON is the value of the monitored variable
TARGET is the target value
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Warnings
Controlled value less than lower bound!
Controlled value greater than upper bound!
Errors
Division by zero in controller!
| Related Topics |
| Controllers Example |