ProSoft Technology MVI46-DNP - Manual (Page 112)

MVI46-DNP ♦ SLC Platform Reference
Master/Slave Communication Module
Page 112 of 143 ProSoft Technology, Inc.
August 23, 2007
5.11 Event Size Computation
The minimum event buffer size required to avoid overflow can be computed as
follows:
((number of static points)*(rate per second scan of change function)) /(rate per
second of master event data poll)
For example: 51 binary input points are scanned two times each second and
polled by the master station about every five seconds. The minimum number of
binary input events is:
(51 * 2)/.02 = 510 events
This computation assumes the unlikely event that all data points will change in
consecutive calls to the scan of change function. If an event buffer overflow
condition occurs, the internal indication bit, BUFFER OVERFLOW, will be set. If
the system you are working with is fairly stable, the following equation can be
used to compute the event buffer size:
(number of points that change per change function * rate per second of scan of
change function)*(number of seconds between master event data poll)
For example:
1000 binary input points are scanned two times each second and
polled by the master station about every five seconds. Only about five points
change state every scan of the change function call.
(5 * 2) * 5 = 50 events required
The number of events that can be defined in the system is limited to 400. The
event buffer will overflow in systems which are very dynamic unless one of the
following conditions exist:
ƒ The master frequently polls the slave device for events to keep the buffer
empty.
OR
ƒ
The slave is configured to send unsolicited messages to the master station.
This method requires full-duplex operation of the network because the slave
may be sending a message during a request from the master station.
In order to disable the report by exception feature in the module, set the number
of events to 0 for the BI Class, AI Class, and Float Class parameters within the
DNP.CFG files. This will cause the slave to never generate event data for
classes 1, 2, or 3.