Echelon i.LON SmartServer 2.0 - Manual (Page 88)

i.LON SmartServer 2.0 Programmer’s Reference 6-10
Identifier Description
FN_NE Not equal. An alarm will be generated if the input value is not equal to the
compare value.
FN_LIMIT Compare against the limits defined by the high and low limit offset fields. For
more information, see Hysteresis Levels and Offset Limits.
Different comparison functions should be used for different data point types, depending on the
of the data point. The following table lists the different data point base types, and
the comparison functions you can use with them.
Base Type Valid
BT_UNKNOWN, BT_ENUM, BT_ARRAY,
BT_STRUCT, BT_UNION, BT_BITFIELD FN_EQ, FN_NE
BT_SIGNED_CHAR, BT_UNSIGNED_CHAR,
BT_SIGNED_SHORT, BT_UNSIGNED_SHORT,
BT_SIGNED_LONG, BT_UNSIGNED_LONG,
BT_FLOAT, BT_SIGNED_QUAD,
BT_UNSIGNED_QUAD, BT_DOUBLE FN_GT, FN_LT, FN_GE, FN_LE,
FN_EQ, FN_NE, FN_LIMIT
You can make inequality comparisons between SNVT_switch (BT_STRUCT) data points, or between
SNVT_lev_disc (BT_ENUM) data points. The following table lists the
identifiers you could use for these special comparisons. A description of how these comparisons are
made follows the table.
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.
6.3.2.3 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.
The following table 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.