RMS Compact II
Version 1.0.7 September 2016
Page 53
8 Appendix B: Hysteresis
Demystified
How Hysteresis works
When a temperature or humidity limit is reached and the relevant limit has its ‘OFF to
ON Trap’ enabled an alarm trap will be issued by the RMS Compact II for this event.
With a zero hysteresis setting the traps will continue to be generated each time the
limit is reached.
This may be undesirable in a situation where the temperature or humidity level
measure has only reduced by a small amount before rising again and triggering further
traps.
The hysteresis function is provided to prevent further alarm traps from being
generated until the measured value has fallen to a satisfactory level.
Figure 8-1.
Hysteresis chart
As shown in the humidity first rises past its upper warning threshold which generates
a trap.
The humidity then reduces slightly but does not reduce to the hysteresis level which is
1.5% RH lower than the alarm (1.5% RH lower as an absolute measured value rather
than 1.5% of currently measured value).
Humidity then increases and decreases again. However on the second decrease of
humidity the level drops below the hysteresis level. The
Alarm Trap
No Traps
Alarm Trap
Upper Limit
(25.0)
Hysteresis
Threshold
Normal Trap
(23.5)
