Echelon i.LON 100 e2 Internet Server - Manual (Page 81)

i. LON 100 Internet Server Programmer’s Reference 6-9
Property Description
This property applies to scalar data points only. Specify the
change in value required for an entry to the log to be made. For
example, if this property is set to 30.0, the value of the data
point being monitored must change by at least 30.0 during an
update for the change to be recorded by the Data Logger. All
updates are logged if this value is 0.0, or not defined.
This property has minimum and maximum floating point values
of +/-3.402823466e+038.
NOTE: If the format type used by the data point being
monitored is SNVT_temp_p#US or SNVT_temp#US, then the
value of this property returned by the DataLoggerGet function
will be displayed using the SNVT_temp_f#US_diff format type.
This rule applies to all formats that use the #US specifier.
The poll rate for the Data Logger can be between 0 and
214,748,364.0 seconds. The Data Logger will check for updates
to the data point at this interval. Echelon recommends that you
set this to a value greater than or equal to the value specified for
the property if you do not want to poll
data before updates to the log are possible.
If you use the default poll rate of 0 seconds, the Data Logger will
record each updates to the data points it is monitoring into the
log, assuming that the time period defined by the
property has elapsed and the change
in value specified by the property
has been met.
You should note that other
i. LON 100 applications may cause
the Data Server to poll this data point’s value as well. The poll
rate specified by these applications should be compatible with
each other. For example, if an Alarm Generator is polling a data
point every 15 seconds, and the Data Logger is polling that data
point every 10 seconds, then the Data Server will have to poll
the value of the data point every five seconds to ensure that each
application gets a current value for each poll.
It is important to note this as you set poll rates for various
applications, as you may end up causing more polls than is
efficient on your network. For example, if an Alarm Generator is
polling a data point every 9 seconds and a Data Logger is polling
a data point every 10 seconds, the Data Server would have to
poll the data point every second to ensure that each application
polls for a current value. This may create a significant amount of
undesrired traffic.