Fabric Watch Administrator's Guide v7.0.0 (53-1002153-01, April 2011)

Fabric Watch Administrator’s Guide 17
53-1002153-01
Time bases
2
Time bases
Time bases specify the time interval between two samples to be compared. You can set the time
base to day (samples are compared once a day), hour (samples are compared once an hour),
minute (samples are compared every minute), or second (samples are compared every second).
This configurable field affects the comparison of sensor-based data with user-defined threshold
values.
Time base set to none
If you set a time base to none, Fabric Watch compares a data value against a threshold boundary
level. When the absolute value of the measuring counter exceeds the threshold boundary, an event
is triggered.
Figure 2 shows a high limit of 65° Celsius placed on a counter measuring temperature. During
each sample period, Fabric Watch measures the temperature and compares it to the high
threshold. If the measured temperature exceeds the high threshold, it triggers an event.
FIGURE 2 Time base set to none
Time base set to other than none
If you specify a time base value other than none (minute, hour, or day), Fabric Watch does not use
the current data value. Instead, it calculates the difference between the current data value and the
data value as it existed one time base ago. It compares this difference to the threshold boundary
limit.
For example, if you specify the time base minute, Fabric Watch calculates the counter value
difference between two samples a minute apart. It then compares the difference (current data
value – data value one minute ago) against the preset threshold boundary.
When you set a time base to a value other than none, there are two main points to remember when
configuring events:
• Fabric Watch triggers an event only if the difference in the data value exceeds the preset
threshold boundary limit.
• Even if the current data value exceeds the threshold, Fabric Watch does not trigger an event if
the rate of change is below the threshold limit.