Operating Manual

Accu-Wave Chapter 3 Set up Level, Level Alarms, and Volume
TN Technologies 3-7
Alarms: Set Point, Clear Point, and Dead Band
An alarm is defined with either a set point - clear point configuration, as shown in Figure
3.4, or a set point - dead band configuration, as shown in Figure 3.5.
The set point defines the measurement value, either level or distance for the primary
measurement, at which the alarm is activated. The clear point or the dead band defines the
measurement value at which the alarm is cleared (alarm ceases).
A clear point sets a fixed measurement value at which the alarm clears. The position of the
clear point is independent of the set point and remains the same even if the set point is
moved. As illustrated in Figure 3.4, changing the set point from 3.0 m to 3.5 m has no
effect on the clear point which remains at 2.0 m.
Figure 3.4 Set Point / Clear Point Alarm
A dead band defines a fixed distance between the set point and an implicit clear point. If
the set point is moved, the implicit clear point moves also, maintaining the distance from
the set point specified by the dead band. As illustrated in Figure 3.5, changing the set point
from 2 m to 3 m moves the implied clear point from 4 m to 5 m. The relative distance
between the implied clear point and the set point remains fixed at 2 m, the dead band
value.
If you may want to later change the alarm set point without affecting the point where the
alarm is cleared, use a clear point configuration. Alternately, if you want the alarm clear
point to be defined at a fixed distance relative to the set point, use a dead band
configuration.
b. Modified Set
Point /Clear Point
a. Initial Set Point
/Clear Point Alarm
3.0 m
Clear Point
New
Set Point
Clear Point
Initial
Set Point
2.0 m
3.5 m