Echelon OpenLNS Commissioning Tool - Manual (Page 190)

174 Monitoring and Controlling Networks
You can update all network variable values by clicking the Refresh All button ( ) on the browser
toolbar or opening the Browse menu and selecting Refresh All.
Using Bound Updates
You can use bound updates with the OpenLNS CT Browser to reduce the network overhead of polling
many network variables. Bound updates use a connection between the network variable being
monitored and the browser. To enable bound updates for a network variable, right-click a network
variable row, click Properties on the shortcut menu, click the Monitoring tab and then select the Bind
this Network Variable to the Browser check box. This creates an implicit connection to the browser.
An implicit connection is a network variable connection that is automatically created by the browser.
You can also explicitly create bound connections to the OpenLNS CT browser which are in turn
automatically used by the browser instead of polling as described in Binding Network Variables to the
Host.
Each implicit connection requires a network variable on the OpenLNS CT computer, and consumes
network variable binding resources on the sending device or devices. This creates unnecessary
network variables and consumes unnecessary resources if you are using bound monitoring with many
network variables of the same type. To reduce the number of network variables on your computer and
reduce network variable binding resource consumption, you can use one of the following methods:
• Use polled monitoring by clearing the Bind this Network Variable to the Browser check box.
• Explicitly bind the network variable to the host as described in Binding Network Variables to the Host.
• Use aliases on the devices that are bound to the fan-in connection.
• Define more aliases on the device containing the network variable with the fan-in connection.
Binding Network Variables to the Host
You can bind network variables to the OpenLNS CT host to receive event-driven updates for
monitoring. You can use event-driven updates to minimize the monitoring network overhead
associated with inputs that change infrequently such as digital sensors. Event-driven updates may
generate excessive network traffic if the updates are frequent.
You can set up event-driven updates using the OpenLNS CT Browser, as described in Using Bound
Updates. The method described there implicitly creates a new network variable on the OpenLNS CT
host for each network variable to be monitored using bound monitoring. If a network variable or
connection cannot be created, bound connections are not used and no error message is displayed
To optimize host network variable usage, you can bind many network variables into a single host
network variable. This is called a fan-in connection. For example, in a system containing several
thousand devices, each of which has an output network variable that indicates its alarm state, separate
connections between each of these network variables and the host would consume a significant amount
of system resources. It is more efficient to create just one network variable on the host and bind all of
the output network variables to it. Network variables bound to the host may be monitored by an
OpenLNS application such as the LNS DDE Server. OpenLNS allows the individual network
variables to be monitored, even though they are received on the same network variable input on the
host. Therefore, there is no disadvantage to using a fan-in connection. To differentiate between the
different inputs, OpenLNS applications should monitor the network variables on the remote devices
instead of the network variables created on the OpenLNS CT computer. OpenLNS automatically uses
event-driven updates if a connection to the OpenLNS CT computer exists.
To create a network variable on the host, follow these steps:
1. Add a virtual functional block to your OpenLNS CT drawing.
a. Drag the generic functional block SmartShape from the OpenLNS CT Basic Shapes stencil
to the OpenLNS CT drawing. The Functional Block Wizard opens
b. Under the Device box, select OpenLNS Network Interface from the Name list.
c. Under the Functional Block box, select Virtual Functional Block from the Name list.