Filter
Top Products
Configuration and Use Manual 65
Configuration
Startup ConfigurationCalibrationBefore You Begin Startup ConfigurationCalibrationBefore You Begin Startup ConfigurationCalibrationBefore You Begin Startup ConfigurationCalibrationBefore You Begin
4.9.2 Alarm hysteresis
The alarm hysteresis value is a percentage of the output scale. After a process alarm is created, the
transmitter will not create new alarms unless the process first returns to a value within the range of the
alarm hysteresis percentage. Figure 4-9 shows the transmitter’s alarm behavior with an alarm
hysteresis value of 50%.
Note the following about hysteresis:
• A low hysteresis value allows the transmitter to broadcast a new alarm every time or nearly
every time the process variable crosses over the alarm limit.
• A high hysteresis value prevents the transmitter from broadcasting new alarms unless the
process variable first returns to a value sufficiently below the high alarm limit or above the low
alarm limit.
Figure 4-9 High versus low alarm hysteresis values
To change the alarm hysteresis value, refer to the flowcharts in Figure 4-10.
Figure 4-10 Changing the alarm hysteresis
Process variable
Alarm created
Hysteresis value
New alarms
not created
LOW ALARM
HIGH ALARM
New alarm
created here
EDD Bus parameters