Echelon i.LON 100 e2 Internet Server - Manual (Page 102)

i. LON 100 Internet Server Programmer’s Reference 7-13
You can make inequality comparisons between SNVT_switch (BT_STRUCT) data points, or
between SNVT_lev_disc (BT_ENUM) data points. Table 26 lists the
identifiers you could use for these special comparisons. A description of how these
comparisons are made follows Table 26.
Table 26 Exceptions to Base Types and Comparison Functions
SNVT Valid
SNVT_switch FN_GT, FN_LT, FN_GE, FN_LE, FN_EQ, FN_NE
SNVT_lev_disc FN_GT, FN_LT, FN_GE, FN_LE, FN_EQ, FN_NE
Comparisons made with SNVT_switch data points are enumeration-based comparisons
based on the value field of the SNVT_switch. If the value field is between 0.5 and 100.0, the
SNVT_switch is considered ON and that will be the basis of the comparison. If the value field
is between 0.0 and 0.4, the SNVT_switch will be considered OFF. In this way you could
compare SNVT_switch data points. For example, if the input data point was ON, the
compare data point was OFF, and the comparison function selected was FN_GT, the
comparison would return True because ON is considered greater than OFF.
This is also true for SNVT_lev_disc data points, which take five enumerations: OFF, LOW,
MEDIUM, HIGH, and ON. If the input data point was LOW, the compare data point was
HIGH and the comparison function was FN_GT, the function would return False, because
LOW is not greater than HIGH.
7.2.1.2.3 Hysteresis Levels and Offset Limits
The four offset limit properties are named ,
, , and . The
Alarm Generator will use these offsets to determine if an alarm condition exists when the
selected for the Alarm Generator is FN_LIMIT.
Table 27 lists the four offset limits, and the condition set that causes each one to generate an
alarm. It also lists the status that the of the input and alarm data
points will be updated to when an alarm is generated based on each offset limit in the Alarm
Status column.
Table 27 Hysteresis Levels and Offset Limits
Offset Limit Alarm Generated When.... Alarm Status
Input Value>Compare Value + UCPThighLimit1Offset AL_HIGH_LMT_ALM1
Input Value>Compare Value + UCPThighLimit2Offset AL_HIGH_LMT_ALM2
Input Value AL_LOW_LMT_ALM1
Input Value AL_LOW_LMT_ALM2
Each time an alarm is generated based on any of these offset limits, the value of the input
data point must return to a value inside the hysteresis range for that limit, and the time
period specified by the property must elapse, before the alarm is cleared.
Only then could another alarm be generated based on that offset limit.
The Alarm Generator’s hysteresis levels determine the value the input data point must
return to for each alarm condition to be cleared. Table 28 describes how these levels are
calculated for each of the offset limits listed above.