Typically, you create multiple tuning policies in a BacnetNetwork—especially if you have multiple Bacnet network ports enabled. This allows you to reference different tuning policies from Bacnet proxy points under different networks (often with vastly different performance capabilities). For example, points under a Bacnet MSTP network would likely use different tuning policies than those under a Bacnet IP network.
You can add a tuning policy in the BacnetNetwork’s property sheet by simply right-clicking an existing policy, then choosing in the shortcut menu. Name it as desired, and edit its properties as needed. Or, drag a BacnetTuningPolicy from the palette, dropping it in the network’s TuningPolicies container, and edit as needed.
Also, if you have client BacnetDevices that provide support for COV notifications, you typically add at least one tuning policy that has its “Use Cov” property set to True (and possibly with other adjustments), see Figure 13.
Then, when adding/editing proxy points under such COV-capable devices, you can specify to use this (COV-specific) tuning policy.
Also see the two next sections:
In addition to properties typical to most Tuning Policies, the Bacnet driver provides these properties:
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Use Cov
Default is False. If set to True, and assigned proxy points are under a BacnetDevice that supports the Subscribe COV service, any necessary updates (Niagara proxy subscriptions) are attempted using BACnet COV subscriptions to the device. If the subscription attempt succeeds, the “Read Status” property of the point’s BacnetProxyExt displays “
COV”. If the subscription attempt for a proxy point fails, normal polling is used and the “Read Status” property shows “Polled”. -
Use Confirmed Cov
If Use Cov is enabled (True) and assigned proxy points are under a BacnetDevice that supports Confirmed COV notifications, any necessary updates (Niagara proxy subscriptions) are attempted using BACnet Confirmed COV subscriptions to the device. If Use Cov is disabled (False), it makes no difference what this property value is. The default value is True.
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Cov Subscription Lifetime
The lifetime, in minutes, for which Niagara will subscribe for COV notifications, then (if necessary) periodically re-subscribe. A value of zero means an indefinite lifetime, although this is not guaranteed to persist across resets of the server device. The default value is 15 minutes.
In general, you should never set the “Stale Time” property in a Tuning Policy shorter than the poll cycle time, or else points will go stale in the course of normal polling. Instead, set the stale timer to be longer than the largest expected poll cycle time. This period can vary depending on how many Px graphics are being viewed, and so on.
Also, note that for each point, the stale timer is measured from the last time the point was updated. This means if you have a 10-minute stale timer, and an 8-minute poll cycle time, you will have some points with values nearly 8 minutes old. If you stop polling, those points will begin going stale roughly 2 minutes after polling has stopped, and not 10 minutes.
This has resulted in some confusion—where the expectation was that after viewing a graphic, any points in it should stay up for the 10 full minutes (or the configured Stale Time) before going stale. However, the actual time depends on how long ago they were last polled.