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
