23
100
50
1
2
3
4
t
(191 secs)
Hours
% Engineering Range
Alarm Off
Alarm On
t
(191 secs)
5
4
CONFIGURATION MODE…
Note.
Fast/Slow Rate Alarms
– an alarm becomes active when the rate of change in
the process variable is faster or slower than the configured alarm value. Rate
of change alarm values are configured as a % of span change per hour. The
elapsed time period before the alarm condition is detected is dependant
upon the configured alarm value. This period can be calculated as follows:
t = 10.81 +
1800
trip value (as a % of eng. span/hr)
t = 191 seconds
The alarm remains active until the rate of change in the process variable
returns to the non-alarm condition. The calculated time period (t) elapses
between the process variable reaching the non-alarm condition and the
alarm becoming inactive.
Fig. 4.5 Rate Alarms
…4.3.2
Alarms – Figs. 4.3, 4.4, 4.5 and 4.6
