User manual

IEC61131 User and Reference Manual
April 22, 2008
505
Poll Offset Example
The Poll Offset parameter enhances the control over timing of master poll messages, by allowing
master poll messages to be staggered.
For example, a master station may have 10 slaves to poll, and must poll them every hour. If these are
included in the poll table without any poll offset, they will all be polled in quick succession on the
hour – resulting in a large burst of communication activity once per hour. On some types of
communications networks (particularly radio) it is desirable to distribute communication load more
evenly, to minimize the chance of collisions and to avoid the possibility of consuming bandwidth
continuously for an extended period of time.
The poll offset parameter enables you to distribute the communication load evenly. In the above
example, it is possible to stagger the master polls so slave stations are polled at 6-minute intervals.
To do this, set the base poll interval to 10 seconds, and for each slave station set the poll rate and poll
offset parameters as follows:
Base Poll (seconds) Poll Rate (seconds) Poll Offset (seconds)
10 360 0
10 360 36
10 360 72
10 360 108
10 360 144
10 360 180
10 360 216
10 360 252
10 360 288
10 360 324
Address Mapping
The Address Mapping property page is selected for editing by clicking Address Mapping in the tree
control section of the DNP Settings window. This selection is only visible if the controller type is a
SCADAPack 330, SCADAPack 350, SCADAPack 32 or SCADAPack 32P. These controllers
support DNP Master.