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EXCEL 50/100/500/600/800 ATTRIBUTES
EN2B-0092GE51 R0512
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maintained” will be 120 hours. By comparing the attributes "Maintenance Alarm"
and "Last Maintained", the user can see that the next maintenance period will be
after an additional 380 hours have elapsed. If the maintenance alarm is reached,
and the maintenance work has been performed, the counter can be reset manually.
The counter can also be reset manually before reaching the maintenance alarm if,
for instance, the maintenance has been performed earlier. If the counter is not
reset, on expiration of the maintenance alarm, e.g. after 500 hours, the elapsed
hours run continues to be incremented, and an additional alarm will be generated
when 1000 hours running has been reached.
Hysteresis
The following hysteresis attributes allow the user to control the triggering conditions
based on a changing parameter under which actions are taken, such as alarm
signaling, writing values to buffers, etc. A hysteresis can be used, e.g., to prevent
an alarm from being generated unless the value being monitored changes by more
than a given value. This eliminates unnecessary alarm generation and reduces bus
communication traffic.
Alarm Hysteresis
Alarm hysteresis (V1.5.x) In the case of analog inputs and pseudo analog points, the attribute "Alarm
Hysteresis" is available. It provides variable hysteresis that can be implemented,
e.g., in order to reduce the cost of communicating with a remote front-end. The
hysteresis value is set from an MMI and can have a value anywhere in the range
defined by [10
-a
to (Max1 - Min1)] where “a” is the number of decimal places set in
the attribute "Engineering Unit". The minimum value for the hysteresis is 10
-a
.
Alarms are generated under the following conditions:
• Max 1 Alarm (generated if MAX 1 is exceeded)
• Max 2 Alarm (generated if MAX 2 is exceeded)
• Max 2 Normal (generated if the value falls below MAX 2-Hysteresis)
• Max 1 Normal (generated if the value falls below MAX 1-Hysteresis)
• Min 1 Alarm (generated if the value falls below MIN 1)
• Min 2 Alarm (generated if the value falls below MIN 2)
• Min 2 Normal (generated if the value MIN 2+Hysteresis is exceeded)
• Min 1 Normal (generated if the value MIN 1+Hysteresis is exceeded)
The CARE default value (i.e. 1% of actual value and no less than 0.2) for this
attribute is 0. Access to "Alarm Hysteresis" is also possible via RIA/WIA.
NOTE: The number of decimal places can be changed only using CARE.
NOTE: Attempting to enter a hysteresis value that is less than the allowed
minimum will result in the attribute being assigned the minimum value as
defined above.
Example:
In this example, the number of decimal places in the attribute "Engineering Unit"
has been chosen to have a value of 2. Fig. 11
shows an example datapoint value
as a function of time that increases and decreases over the range from Max 1 to
Min 1.