Alarm on Deviation
(Original Document)
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Description
This function monitors changes in the deviation between the process value (PV) and the setpoint (SP), by comparing these 2 values to 2 thresholds (high deviation threshold and low deviation threshold).
These alarms are controlled by a fixed hysteresis of 1% of the full scale of the loop.
NOTE: The threshold values must be greater than the hysteresis (1%), otherwise the alarms will still be active.
Alarm on deviation function diagram:
Parameters
Input parameters:
Parameter
Symbol
Type
Thresholds
Default Value
R/W
Process Value
PV
REAL
-3.4E38 / 3.4E38
/
R
Setpoint Value
SP
REAL
-3.4E38 / 3.4E38
/
R
Internal Parameters:
Parameter
Symbol
Type
Thresholds
Default Value
R/W
High deviation threshold
DEV_H
REAL
0.0 / 3.4E38
5.0
R/W
Low deviation threshold
DEV_L
REAL
-3.4E38 / 0.0
-5.0
R/W
Output Parameters:
Parameter
Symbol
Type
Thresholds
Default Value
R/W
Upper Limit
STS_DEVH
EBOOL
/
/
R
Lower Limit
STS_DEVL
EBOOL
/
/
R
Or alarms (*)
STS_ALARMS
EBOOL
/
/
R
NOTE: (*) Or alarms = Or bit logic on level alarms and alarms on deviation.
Execution Monitoring
The monitoring of parameters is integrated into the error management of the Process Value branch.